Effects of Celsior and University of Wisconsin preservation solutions on hemodynamics and endothelial function after cardiac transplantation in humans: a single-center, prospective, randomized trial

Optimal preservation of the myocardium remains a major concern in clinical and experimental heart transplantation. The present study compared the efficacy of University of Wisconsin (UW) and Celsior preservation solution with respect to myocardial performance, epicardial and microvascular endothelial vasomotor function and myocardial expression of endothelin and nitric oxide synthases in humans. Forty-one cardiac transplant recipients received either UW (n = 20) or Celsior (n = 21) preserved hearts. Catecholamine and vasodilator requirements were assessed within the first 5 postoperative days. Left ventricular performance and endothelial function was assessed 1 month after transplantation. Endothelin and nitric oxide synthase gene expression were detected in myocardial biopsy samples. Celsior preserved hearts required significantly more catecholamines and vasodilators within the first 5 postoperative days. Myocardial performance and endothelial function were comparable 1 month after transplantation. Total ischemic time correlated with impaired endothelial function in the Celsior but not in the UW group. Endothelin and inducible nitric oxide synthase gene expression were significantly higher in the Celsior group. The results of the study show that both solutions provide myocardial protection with regard to left ventricular performance and endothelial function 1 month after cardiac transplantation. The necessity for higher vasodilator and catecholamine therapy in Celsior preserved hearts suggests post-ischemic myocardial stunning within the first 5 postoperative days. The positive correlation between impaired endothelial function and total ischemic time in the Celsior group requires longitudinal investigation in particular with regard to the development of allograft vasculopathy.

Skeletal muscle reperfusion injury: reversal by controlled limb reperfusion--a case report

Despite successful surgical revascularization of ischemic limbs, a local and systemic reperfusion injury may occur after normal blood reperfusion. Recent experimental and clinical application of controlled limb reperfusion in Europe has demonstrated superior results, with lower morbidity and mortality. This new surgical technique includes modification of the reperfusate (calcium, pH, substrates, osmolarity, free radical scavenger) and the circumstances of initial reperfusion (time, temperature, pressure). This report describes the first application of controlled limb reperfusion after reperfusion injury. A 16-year-old boy underwent femoral access cardiopulmonary bypass for repeat cardiac repair with an ischemic time of 245 minutes. Postoperatively, severe ischemia/reperfusion syndrome developed with muscle contracture, immobility, and anesthesia of the right leg with a second ischemic time of about 6 hours. The systemic creatine phosphokinase level was 88,000 U/L; myoglobin was 27,000 ng/mL. He underwent controlled limb reperfusion by withdrawing blood from the aorta and mixing it with a crystalloid solution (calcium-reduced, hyperosmolar, hyperglycemic, alkalotic, glutamate- and aspartate-enriched, and containing a free radical scavenger) under controlled conditions (blood:crystalloid solution 6:1, for 30 minutes, reperfusion pressure < 50 mm Hg, and normothermia) before establishing normal blood reperfusion. Metabolic data from the central and femoral vein demonstrated a significant reduction of all previous elevated enzyme levels, avoidance of hyperkalemia, normalization of acidosis, and avoidance of systemic reperfusion injury with no multiorgan failure. Limb salvage was accomplished and functional recovery almost complete. To the authors' knowledge, this is the first application of controlled limb reperfusion reported in North America. With this surgical technique we were able to prevent metabolic local and systemic reperfusion changes after prolonged ischemia and also reduced previous reperfusion changes. This report confirms former experimental data, and further clinical studies are warranted.

Myocardial protection in hypoxic immature hearts

Current myocardial protection techniques in cyanotic immature hearts are not optimal. Despite successful surgical correction of congenital cardiac defects causing hypoxemia, myocardial dysfunction remains the leading cause of postoperative mortality. New studies indicate that the intraoperative reintroduction of molecular oxygen on cardiopulmonary bypass causes a reoxygenation injury leading to postoperative cardiac dysfunction. Biochemical and functional changes of reoxygenation injury can be avoided by several methods aimed at reducing oxygen free radical production and nitric oxide release. The present investigation provides an overview of our current understanding of pathogenesis, implication, and treatment of myocardial reoxygenation injury. New surgical concepts of myocardial protection including normoxic CPB and controlled reoxygenation are introduced.

Reduced oxygen tension during cardiopulmonary bypass limits myocardial damage in acute hypoxic immature piglet hearts

OBJECTIVES

Cardiopulmonary bypass (CPB) is usually instituted in a hyperoxic fashion (oxygen tension (pO2) 300-500 mm Hg), which may expose cyanotic infants to potential reoxygenation damage. Oxygen free radicals play an important role in this injury. The rate of production of this highly reactive toxic oxygen species is dependent on the oxygen level during reoxygenation. This study tested the hypothesis that reduction of the oxygen in the bypass prime and in blood cardioplegia (BCP) to normoxic levels can reduce reoxygenation injury and will result in improved contractility.

METHODS

We operated on 19 Duroc-Yorkshire piglets (2-3 weeks, 3-5 kg). Five underwent 30 min of BCP arrest during 1 h of CPB without hypoxia (control). Fourteen underwent 120 min of hypoxia (arterial pO2 20-30 mmHg) on ventilator before reoxygenation on CPB. Reflecting the clinical routine procedure, nine of them were reoxygenated on CPB for 5 min with high pO2 (350-450 mm Hg) followed by 30 min of BCP arrest (high pO2) and 25 min of reoxygenation/reperfusion on CPB with high pO2 levels (NoRx). Five others were put on CPB with pO2 reduced to normoxic levels (pO2 100 mm Hg) in CPB and BCP (Rx). Functional and biochemical measurements were made before hypoxia, as well as during and after reoxygenation.

RESULTS

In contrast to controls, NoRx resulted in a 40% decrease in antioxidant reserve capacity (P<0.01) at 4 mM t-butyl hydroperoxide (t-BHP), a 1212% increase in myocardial conjugated diene production during BCP induction (P<0.0003), a 1000% during reperfusion (P<0.002), a 36.1% and a 37.0% increase in coronary sinus blood conjugated dienes at 35 min (P<0.05) and 60 min (P<0.05) of reoxygenation. These biochemical changes were accompanied by a 79% reduction of left ventricular contractility (P<0.0003). Conversely, Rx led to an improvement in antioxidant reserve capacity (939+/-212 vs. 1342+/-177 nmol/g protein; P<0.003), less conjugated diene production during BCP induction (15.5+/-6.1 vs. 42.1+/-8.8 A233 nm/min per 100 g; P<0.003) and reperfusion (1.8+/-3.9 vs 22.0+/-5.5 A233 nm/min per 100 g; P<0.005), and to a significantly improved post bypass LV contractility (58+/-25 vs. 21+/-5; P<0.0003).

CONCLUSIONS

These data document that hypoxemic/reoxygenation injury occurs in acute hypoxic immature piglet hearts when reoxygenated on CPB with hyperoxic pO2 (normal clinical practice). By lowering the antioxidant reserve capacity, hypoxemia seems to render the developing heart susceptible to reoxygenation damage, which occurs with the reintroduction of molecular oxygen, and is associated with free radical production, subsequent lipid peroxida tion, and depressed post bypass LV function. Reduction of pO2 during the initial reoxygenation period and during BCP arrest to normoxic levels resulted in a significant reduction of this oxygen-related damage and in much improved myocardial performance.

Normoxic cardiopulmonary bypass reduces oxidative myocardial damage and nitric oxide during cardiac operations in the adult

OBJECTIVE

Hyperoxic cardiopulmonary bypass is widely used during cardiac operations in the adult. This management may cause oxygenation injury induced by oxygen-derived free radicals and nitric oxide. Oxidative damage may be significantly limited by maintaining a more physiologic oxygen tension strategy (normoxic cardiopulmonary bypass).

METHODS

During elective coronary artery bypass grafting, 40 consecutive patients underwent either hyperoxic (oxygen tension = 400 mm Hg) or normoxic (oxygen tension = 140 mm Hg) cardiopulmonary bypass. At the beginning and the end of bypass this study assessed polymorphonuclear leukocyte elastase, nitrate, creatine kinase, and lactic dehydrogenase, antioxidant levels, and malondialdehyde in coronary sinus blood. Cardiac index was measured before and after cardiopulmonary bypass.

RESULTS

There was no difference between groups with regard to age, sex, severity of disease, ejection fraction, number of grafts, duration of cardiopulmonary bypass, or ischemic time. Hyperoxic bypass resulted in higher levels of polymorphonuclear leukocyte elastase (377 +/- 34 vs 171 +/- 32 ng/ml, p = 0.0001), creatine kinase 672 +/- 130 vs 293 +/- 21 U/L, p = 0.002), lactic dehydrogenase (553 +/- 48 vs 301 +/- 12 U/L, p = 0.003), antioxidants (1.97 +/- 0.10 vs 1.41 +/- 0.11 mmol/L, p = 0.01), malondialdehyde (1.36 +/- 0.1 micromol/L,p = 0.005), and nitrate (19.3 +/- 2.9 vs 10.1 +/- 2.1 micromol/L, p = 0.002), as well as reduction in lung vital capacity (66% +/- 2% vs 81% +/- 1%,p = 0.01) and forced 1-second expiratory volume (63% +/- 10% vs 93% +/- 4%, p = 0.005) compared with normoxic management. Cardiac index after cardiopulmonary bypass at low filling pressure was similar between groups (3.1 +/- 0.2 vs 3.3 +/- 0.3 L/min per square meter). [Data are mean +/- standard error (analysis of variance), with p values compared with an oxygen tension of 400 mm Hg.]

CONCLUSIONS

Hyperoxic cardiopulmonary bypass during cardiac operations in adults results in oxidative myocardial damage related to oxygen-derived free radicals and nitric oxide. These adverse effects can be markedly limited by reduced oxygen tension management. The concept of normoxic cardiopulmonary bypass may be applied to surgical advantage during cardiac operations.

Delayed cardioplegic reoxygenation reduces reoxygenation injury in cyanotic immature hearts

BACKGROUND

Hypoxemic developing hearts are susceptible to oxygen-mediated damage that occurs after reintroduction of molecular oxygen. This unintended hypoxemic/reoxygenation injury leads to lipid peroxidation and membrane damage and may contribute to postoperative cardiac dysfunction. Biochemical and functional status are improved by delaying reoxygenation on cardiopulmonary bypass (CPB) until cardioplegic arrest.

METHODS

Six immature piglets (3 to 5 kg) without hypoxemia underwent 30 minutes of cardioplegic arrest during 1 hour of CPB. Fourteen others underwent 2 hours of hypoxemia on ventilator before reoxygenation on CPB. Reflecting our clinical routine, 9 were reoxygenated on CPB for 5 minutes followed by 30 minutes of cardioplegic arrest and 25 minutes of reperfusion. The other 5 were put on hypoxemic CPB for 5 minutes, before being reoxygenated during cardioplegic arrest for 30 minutes followed by 25 minutes of reperfusion.

RESULTS

Cardioplegic arrest (no hypoxemia group) caused no functional or biochemical changes. In contrast, by preceding hypoxemia with subsequent reoxygenation on CPB (no treatment group) we found 39.5% decrease in antioxidant reserve capacity, 1,212% increase in myocardial conjugated diene production, significant increase in coronary sinus blood conjugated dienes, and an 81% reduction of left ventricular contractility, all of which were statistically significant (p < 0.05) when compared with the no hypoxemia group. Conversely, delaying reoxygenation until cardioplegic arrest (treatment group) resulted in 33.1% improvement in antioxidant reserve capacity, 91.7% less conjugated diene production, lower coronary sinus blood conjugated diene levels, and a 95% improved contractility, all of which were significant (p < 0.05) when compared with the no treatment group.

CONCLUSIONS

A reoxygenation injury associated with lipid peroxidation and decreased postbypass contractility occurs in cyanotic immature hearts when reoxygenated on CPB. Delaying reoxygenation until cardioplegic arrest by starting CPB with ambient partial pressure of oxygen results in significantly improved myocardial status.

Prevention of reoxygenation injury in hypoxaemic immature hearts by priming the extracorporeal circuit with antioxidants

This study tests the hypothesis that abrupt reoxygenation of cyanotic immature hearts when starting cardiopulmonary bypass produces an unintended reoxygenation injury that: (i) nullifies the cardioprotective effects of blood cardioplegia; and (ii) is avoidable by adding the antioxidants, N-(2-mercaptopropionyl)-glycine (MPG) plus catalase to the cardiopulmonary bypass prime. Twenty immature piglets (aged 2-3 weeks) underwent 30 min of blood cardioplegic arrest (BCP) with standard clinical blood cardioplegia (hypocalcaemic, alkalotic, hyperosmolar, substrate-enriched). Six piglets remained normoxaemic (BCP). Fourteen others were made hypoxic (PO2 20-30 mmHg) for up to 2 h by lowering ventilator FiO2 (5-7%) before undergoing reoxygenation on cardiopulmonary bypass at PO2 400 mmHg. In eight animals, the pump prime was not supplemented with antioxidants (Reox + BCP), whereas MPG (80 mg/kg) and catalase (CAT; 5 mg/kg) were added to the pump prime in the other six (MPG/CAT). Myocardial function (end-systolic elastance, conductance catheter), oxidant damage (myocardial conjugated diene production), oxygen consumption and antioxidant reserve capacity were evaluated. Blood cardioplegic arrest caused no functional or biochemical changes in controls without preceding hypoxia. In contrast, hypoxia and reoxygenation in animals undergoing the same blood cardioplegic protocol (Reox + BCP) caused profound myocardial dysfunction, as end-systolic elastance recovered only to 21(2)% (P < 0.05 versus control) of baseline values. Additionally, it reduced antioxidant reserve capacity (malondialdehyde, MDA at 4.0 mM of t-BHP: 1342(59) (P < 0.05 versus control) versus 788(53) mmol/g protein), and led to significantly greater production of conjugated dienes during warm induction (42(4.4) (P < 0.05 versus control) versus 3.3(1.4) A233 nm/100 g per min) and reperfusion (22(2.7) (P < 0.005 versus control) versus 2(0.6) A233 nm/100 g per min). Conversely, supplementation of MPG plus catalase to the pump prime reduced lipid peroxidation (conjugated diene production during warm induction: 22.3(7) A233 nm/100 g per min P < 0.05 versus Reox + BCP), restored antioxidant reserve capacity (MDA at 4.0 M of t-BHP: 975(139) mmol/g protein P < 0.05 versus Reox + BCP) and allowed almost complete functional recovery (80(8)%). Abrupt reoxygenation of hypoxaemic immature hearts on cardiopulmonary bypass causes oxidant damage, nullifies the cardioprotective effects of blood cardioplegia, and leads to reduced myocardial contractility. Antioxidant supplementation of the cardiopulmonary bypass prime avoids these detrimental effects, and results in improved biochemical and functional status.

Nitric-oxide-induced reoxygenation injury in the cyanotic immature heart is prevented by controlling oxygen content during initial reoxygenation

Reintroduction of high levels of molecular oxygen after a hypoxic period is followed by a burst of nitric oxide (NO), peroxynitrite, and oxygen free radicals (OFR), which are highly cytotoxic. This study indicates that hyperoxic reoxygenation of cyanotic immature hearts on cardiopulmonary bypass (CPB) induces a reoxygenation injury and that, by reducing NO and OFR production during institution of CPB with subsequent reoxygenation under blood cardioplegic arrest, this oxygen-related damage can be avoided and biochemical and functional status improved. Of 25 immature piglets (3-5 kg, two to three weeks old), 6 underwent one hour of CPB including thirty minutes of aortic clamping with substrate-enriched modified blood cardioplegia (hypocalcemic, alkalotic, and hyperosmolar; warm induction-cold replenishment-warm reperfusion) without preceding hypoxia (controls). Nineteen others were made hypoxic (arterial [Po2] 20-30 mmHg) for up to two hours by lowering the fraction of inspired oxygen (FIO2) on ventilator. These hypoxic piglets were then reoxygenated on CPB at different Po2 levels (hyperoxic, normoxic, or hypoxic) for five minutes, followed by the aforementioned blood cardioplegic (BCP) arrest regimen. Myocardial conjugated diene (CD) production as a marker of lipid peroxidation, and NO production, determined as its spontaneous oxidation products, nitrite (NO2-) and nitrate (NO3-), were assessed during blood cardioplegic induction, and antioxidant reserve capacity was determined by incubating myocardium in the oxidant t-butylhydroperoxide (t-BHP). Myocardial function was evaluated from end-systolic elastance (Ees, conductance catheter). Blood cardioplegic arrest caused no functional or biochemical changes in normoxic control immature piglets. In contrast, brief reoxygenation at PO2 > 400 mmHg, followed by BCP-arrest (hyperoxic) resulted in marked CD production (42 +/- 4 vs 3 +/- 1 A233 nm/minute/100 g; P < 0.05), and NO production (4500 +/- 500 vs 450 +/- 32 mmol/minute/100 g; P < 0.05) during blood cardioplegic induction, reduced antioxidant reserve capacity (malondialdehyde [MDA] at 4.0 mM of t-BHP: 1342 +/- 59 vs 958 +/- 50 nM/g protein; P < 0.05), and caused profound myocardial dysfunction; Ees recovered only 21 +/- 2% (vs 104 +/- 7; P < 0.05), despite the blood cardioplegic regimen shown to be cardioprotective in control normoxic piglets. Conversely, controlling initial PO2 to normoxic (100 mmHg) or hypoxic (20-30 mmHg) levels reduced lipid peroxidation (CD production 16 +/- 2, 2 +/- 1 A233nm/minute/100 g) and NO production (1264 +/- 736, 270 +/- 182 mmol/minute/100 g), restored antioxidant reserve capacity (MDA at 4.0 mM of t-BHP: 940 +/- 95, 982 +/- 88 nM/g protein), and allowed significant functional recovery (58 +/- 11% and 83 +/- 8%), in a PO2-dependent fashion. The authors conclude that reoxygenation of hypoxemic immature hearts by initiating hyperoxic CPB causes oxidant-related damage characterized by lipid peroxidation, enhanced NO production, and reduced antioxidants, leading to functional depression that nullifies the cardioprotective effects of blood cardioplegia. These detrimental effects can be reduced in a PO2-dependent fashion by controlling initial PO2 on CPB and subsequent reoxygenation during blood cardioplegic arrest.

Deletion polymorphism of the angiotensin I-converting enzyme gene is associated with increased plasma angiotensin-converting enzyme activity but not with increased risk for myocardial infarction and coronary artery disease

BACKGROUND

Previous research has shown that the insertion/deletion (I/D) polymorphism of the angiotensin I-converting enzyme (ACE) gene is a major determinant of plasma ACE activity. It has been suggested that persons with the DD genotype (those who express, on average, the highest levels of circulating ACE) have an increased risk for myocardial infarction and coronary artery disease, particularly if they are otherwise at low risk. Subsequent studies, however, have not confirmed that ACE I/D gene polymorphism is a risk factor for coronary artery disease and myocardial infarction.

OBJECTIVE

To investigate the association between the I/D polymorphism of the ACE gene and the risk for coronary artery disease and myocardial infarction in patients in whom coronary artery disease status was documented by angiography.

DESIGN

Cross-sectional study.

SETTING

University medical center.

PATIENTS

209 male case-patients with coronary artery disease and 92 male controls without coronary artery disease, as documented by coronary angiography.

MEASUREMENTS

Assessment of the cardiac risk profile by questionnaire; classification of patients by the degree of coronary artery stenosis; levels of lipoproteins, apolipoproteins, and fibrinogen; and ACE I/D gene polymorphism assessed by polymerase chain reaction amplification.

RESULTS

Plasma ACE activity was significantly associated with ACE I/D gene polymorphism. The ACE genotype was not associated with the presence of coronary artery disease or myocardial infarction. If a recessive effect of the D allele was assumed (DD compared with DI and II), the relative risk was 1.00 (95% CI, 0.76 to 1.30) for coronary artery disease and 1.03 (CI, 0.77 to 1.38) for myocardial infarction. Results of analyses were also negative when a dominant effect of the D allele was assumed and when low-risk subgroups were examined. The established risk factors age and apolipoprotein B level emerged as the most important risk predictors in multivariate analyses, followed by diastolic blood pressure and fasting glucose levels.

CONCLUSIONS

In an angiographically defined study sample, ACE I/D gene polymorphism was not associated with an increased risk for coronary artery disease or myocardial infarction, despite its effects on plasma ACE activity.

Oxidative insult associated with hyperoxic cardiopulmonary bypass in the infantile heart and lung

Cardiopulmonary bypass (CPB) per se alters many factors simultaneously, including free radical generation, which suggests that conventional hyperoxic CPB may produce oxidative injury in the infantile heart and lung. This study tests the hypothesis that CPB provokes oxidative cardiopulmonary changes and pulmonary endothelial dysfunction in immature piglets that can be prevented by free radical scavengers. We studied 15 2- to 3-week-old piglets. Five served as a control without CPB. Ten piglets underwent 60 min of CPB with a membrane oxygenator (Sarns). In 5 of these 10, the bypass prime was supplemented with N-mercaptopropionylglycine (MPG: 80 mg/kg) plus catalase (50,000 U/kg), whereas the others were not treated. Pre- and post-bypass cardiopulmonary function was measured in terms of left ventricular end-systolic elastance [Ees] by a conductance catheter, the arterial/alveolar pO2 ratio (a/A ratio) and static lung compliance. Conjugated dienes (A233 nm/mg lipid) were measured to detect lipid peroxidation in heart and lung tissue, and myocardial antioxidant reserve capacity [malondialdehyde (MDA) production in cardiac tissue incubated with the oxidant t-butyl hydroperoxide (t-BHP)] was assessed to detect oxidative changes. Pulmonary vascular resistance (PVR) and transpulmonary nitric oxide (NO) production were measured to assess pulmonary endothelial injury. Myocardial antioxidant reserve capacity was significantly reduced after 60 min of CPB, compared to control animals (MDA 779 +/- 100 vs 470 +/- 30 nmol/g protein, p < 0.05 at t-BHP 2.0 mmol/L), without evidence of lipid peroxidation or myocardial dysfunction. Pulmonary vascular resistance after CPB was dramatically increased (83 +/- 12 to 212 +/- 30, p < 0.05) without any change in lung function. In parallel to pulmonary vasoconstriction, NO production was significantly decreased after CPB (from 8.8 +/- 1.4 to 2.5 +/- 0.5 mmol/min/kg, p < 0.05). The addition of antioxidants (MPG+catalase) to the prime significantly improved myocardial antioxidant status (MDA: 604 +/- 30 vs 779 +/- 100 nmol/g protein, p < 0.05) and pulmonary vascular resistance (114 +/- 29 vs 212 +/- 30, p < 0.05 vs no-treatment group). In conclusion, the present study confirms that 1) Cardiopulmonary bypass produces substantial oxidative stress in normal immature myocardium, as assessed by reduced antioxidant reserve capacity; 2) CPB impairs pulmonary endothelial function, characterized by NO production, resulting in pulmonary vasoconstriction; and 3) These deleterious effects can be prevented by the addition of antioxidants (MPG/catalase) to the pump prime.

Pulmonary vasoconstriction due to impaired nitric oxide production after cardiopulmonary bypass

BACKGROUND

Pulmonary hypertension is a serious complication after cardiopulmonary bypass (CPB). This study tests the hypothesis that CPB provokes oxidant-mediated pulmonary endothelial dysfunction, leading to reduced nitric oxide (NO) production and pulmonary vasoconstriction.

METHODS

Twelve piglets underwent 2 hours of CPB. In 6 of them, CPB prime was supplemented with N-mercaptopropionylglycine and catalase, whereas the others were not treated. Left and right ventricular function were evaluated from end-systolic elastance and Starling analysis. Pulmonary vascular resistance and transpulmonary NO production (measuring NO2-, NO3-) were determined to assess pulmonary endothelial function.

RESULTS

Cardiopulmonary bypass caused a significant increase in pulmonary vascular resistance (83 +/- 12 to 212 +/- 30 dynes.cm-5.s kg-1, p < 0.05), associated with a reduction of NO production (8.8 +/- 1.4 to 2.5 +/- 0.5 mumol/min, p < 0.05) and depressed right ventricular function (56 +/- 12% of control), whereas N-mercaptopropionylglycine and catalase added to the CPB allowed a substantial improvement of these deleterious effects of CPB.

CONCLUSIONS

Cardiopulmonary bypass impairs pulmonary NO production, resulting in pulmonary vasoconstriction and right ventricular dysfunction, which can be reduced by antioxidants. These findings imply the validity of NO inhalation therapy for postoperative pulmonary hypertension as a supplementation of endogenous endothelium-derived relaxing factor.

Experimental application of controlled limb reperfusion after incomplete ischaemia

Severe local and systemic complications may occur after revascularization of extremities exposed to prolonged complete or incomplete ischaemia. These complications may be reduced by controlling the reperfusate and the circumstances of the reperfusion period. Ten adult German domestic pigs were exposed to 6 h of incomplete limb ischaemia by occlusion of the left iliac artery. To simulate the clinical situation of embolectomy, the occlusive snares were released after the ischaemic period in five pigs and normal blood flow developed with systemic pressure (uncontrolled reperfusion). In the other five pigs, a controlled reperfusate was delivered at controlled pressure before establishing normal blood reperfusion (controlled reperfusion). At the end of the observation period (90 min after start of reperfusion), the group with controlled reperfusion had a lower mean(s.e.m.) tissue water content (81.8(0.7) versus 84.3(0.7) per cent, P < 0.05, a greater increase in tissue adenosine 5'-triphosphate compared with values at the end of ischaemia (6.2(1.5) versus -2.5(1.8) mumol per g protein, P < 0.03), a higher tissue pH (7.2(0.1) versus 6.8(0.1), P < 0.03), a smaller temperature decrease (0.3(0.2) versus 1.2(0.3) degrees C, P < 0.05), lower concentrations of creatine kinase (355.0(87.5) versus 624.4(73.4) units/l, P < 0.05) and lactate dehydrogenase (LDH) (369.5(42.5) versus 538.4(39.2 units/l, P < 0.03) in the femoral vein blood and lower LDH concentrations (356.5(48.9) versus 546.0(37.8 units/l, P < 0.03) in central venous blood. These data indicate that severe local and systemic damage occurs with uncontrolled (normal blood) reperfusion even after incomplete limb ischaemia, and that these changes can be reduced by delivering a controlled reperfusate under controlled conditions.

Controlled limb reperfusion in patients having cardiac operations

HYPOTHESIS

Severe limb ischemia in patients having cardiac operations may occur after intraaortic balloon pump insertion, prolonged femoral vessel cannulation, percutaneous cardiopulmonary bypass, dissecting aneurysms, or emboli. Normal blood reperfusion can cause a postischemic syndrome that increases morbidity and mortality. This clinical study is based on an experimental infrastructure patterned after controlled cardiac reperfusion. (1) It tests the hypothesis that controlled limb reperfusion (i.e., modifying the composition of the initial reperfusate and the conditions of reperfusion) reduces the local and systemic complications seen after normal blood reperfusion. (2) It reports initial clinical application of this strategy in three cardiac surgery centers.

METHODS

Controlled limb reperfusion was applied to 19 patients with signs of severe prolonged unilateral or bilateral ischemia (including paralysis, anesthesia, and muscle contracture); six patients (32%) were in cardiogenic shock. The mean ischemic duration was 26 +/- 6 hours. The reperfusion method includes a 30-minute infusion into the distal vessels of a normothermic reperfusate solution mixed with the patient's arterial blood (obtained proximal to the obstruction) in a 6:1 blood/reperfusate ratio. Data are mean +/- standard error of the mean.

RESULTS

Sixteen patients (84%) survived with salvaged and functional limbs at the time of discharge. No renal, cardiac, pulmonary, cerebral, or hemodynamic complications developed in the survivors. The three deaths occurred in patients undergoing controlled limb reperfusion while in profound postoperative cardiogenic shock; neither postischemic edema nor contracture developed in any of them.

CONCLUSIONS

These findings show that controlled limb reperfusion can be applied readily with standard equipment that is used for cardiac surgery and may salvage limbs while reducing postreperfusion morbidity and mortality.

[Controlled reperfusion of the extremities for preventing local and systemic damage after prolonged ischemia. An experimental study with the swine model]

Our previous studies in isolated rat hindlimbs using crystalloid perfusion solutions have shown that control of the initial reperfusion reduces postischemic complications. However, no experimental study has been undertaken to evaluate the concept of controlled limb reperfusion experimentally in an in-vivo blood-perfused model and to assess the local as well as systemic effects of normal blood reperfusion and controlled limb reperfusion. Of twenty pigs undergoing preparation of the infrarenal aorta and iliac arteries, six were observed for 7.5 hours and served as controls. Fourteen other pigs underwent 6 hours of complete infrarenal occlusion. Thereafter, embolectomy was stimulated in 8 pigs by removing the aortic clamp and establishing normal blood reperfusion at systemic pressure. In 6 other pigs, control of the composition of the reperfusate and control of the conditions of reperfusion was done during the first 30 min, followed by normal blood reperfusion. Six hours of infrarenal aortic occlusion lead to a severe decrease in high energy phosphates and muscle temperature and a slight increase in creating kinase (CK) and potassium in the systemic circulation. Normal blood reperfusion resulted in severe reperfusion injury: massive edema developed (80.6% vs. 76.6%, p < 0.0009), the tissue showed a marked decrease in oxygen consumption (7.3 +/- 1.1 vs. 14.3 +/- 2.5 mL )2/100 g/min, p < 0.02), glucose consumption (0.19 +/- 0.06 vs. 0.51 +/- 0.03 mg/100 g/min, p < 0.06), tissue ATP (18.3 +/- 1.9 vs. 36.1 +/- 0.9 mumol/g protein, p < 0.000001), total adenine nucleotides (26.3 +/- 2.6 vs. 45.8 +/- 1.5 mumol/g protein, p < 0.00001), muscle pH (5.9 +/- 0.1 vs. 7.3 +/- 0.1, p < 0.000006) and total calcium in the femoral vein (2. +/- 0.1 vs. 2.7 +/- 0.1 mmol/L, p < 0.002). Furthermore, a massive increase was seen in CK concentration (12,743 +/- 2,562 vs. 513 +/- 80 U/L, p < 0.0003), potassium (7.9 +/- 0.3 vs. 4.4 +/- 0.2 mmol/L, p < 0.000001) and muscle rigidity (60 +/- 11 vs. 122 +/- 1 degree, p < 0.00008). In sharp contrast, initial treatment of the ischemic skeletal muscle by controlled limb reperfusion resulted in normal water content (77.6 +/- 0.4 vs. 76.8 +/- 0.3%), oxygen consumption (13.2 +/- 1.6 vs. 14.9 +/- 3.2 mL O2/100 g/min), glucose consumption (0.58 +/- 0.18 vs. 0.46 +/- 0.11 mg/100 g/min), flow (5.4 +/- 1.1 vs. 4.6 +/- 4.6 +/- 0.5 mL/100 g/min) and muscle rigidity (106 +/- 4 vs. 122 +/- 1 degree). Furthermore, controlled limb reperfusion resulted in higher total adenine nucleotides content (78% vs. 57% of control), less tissue acidosis (6.6 +/- 0.2 vs. 5.9 +/- 0.1, p < 0.002), severely reduced CK release (2,618 +/- 702 vs. 12,743 +/- 2.562, p < 0.02) and potassium release (5.1 +/- 0.3 vs. 7.9 +/- 0.3 mmol/L, p < 0.0002) as compared to normal blood reperfusion. In conclusion this study shows that 6 hours of acute infrarenal aortic occlusion will result in a severe reperfusion injury (postischemic syndrome) if normal blood at systemic pressure is given in the initial reperfusion phase. In contrast, initial treatment of the ischemic skeletal muscle by controlled limb reperfusion reduces the metabolic, functional and biochemical alterations.

Studies of hypoxemic/reoxygenation injury: without aortic clamping. VI. Counteraction of oxidant damage by exogenous antioxidants: N-(2-mercaptopropionyl)-glycine and catalase

This study tests the hypothesis that antioxidants administered before reoxygenation can reduce oxygen-mediated damage and improve myocardial performance. Of 25 Duroc-Yorkshire piglets (2 to 3 weeks, 3 to 5 kg) five underwent 60 minutes of cardiopulmonary bypass without hypoxemia (control group), and five others underwent 30 minutes of hypoxemia on cardiopulmonary bypass with a circuit primed with oxygen tension about 25 mm Hg blood followed by reoxygenation on cardiopulmonary bypass (no treatment). In vitro studies were performed to obtain the optimal dosage of the antioxidants N-(2-mercaptopropionyl)-glycine and and catalase to be used in subsequent in vivo experimental studies; cardiac homogenates were incubated in 0 to 5 mmol/L concentrations of the oxidant t-butylhydroperoxide and malondialdehyde production was measured. Fifteen piglets were made hypoxemic on cardiopulmonary bypass for 30 minutes, and the antioxidants N-(2-mercaptopropionyl)-glycine at either 30 or 80 mg/kg body weight or N-(2-mercaptopropionyl)-glycine, 30 mg/kg body weight, and catalase, 50,000 U/kg body weight, were added to the cardiopulmonary bypass circuit 15 minutes before reoxygenation. Left ventricular contractility, which was expressed as end-systolic elastance, was measured by conductance catheter before hypoxemia and after reoxygenation. Myocardial antioxidant reserve capacity was determined after reoxygenation by incubating cardiac homogenates in the oxidant t-butylhydroperoxide and measuring subsequent malondialdehyde elution. The in vitro bioassay studies showed a dose-dependent reduction of lipid peroxidation with N-(2-mercaptopropionyl)-glycine, with maximal benefits of a 40% decrease and malondialdehyde elaboration occurring with N-(2-mercaptopropionyl)-glycine and catalase compared with untreated cardiac homogenates. Cardiopulmonary bypass (no hypoxemia) caused no oxidant damage or changes in contractile function after cardiopulmonary bypass. Reoxygenation without treatment raised conjugated diene levels 57%,* lowered antioxidant reserve capacity 51%,* and was associated with only 38%* recovery of contractile function (p < 0.05 vs control). In contrast, treatment with antioxidants avoided lipid peroxidation, maintained antioxidant reserve capacity, and resulted in a dose-dependent improvement in left ventricular contractility with complete recovery occurring in N-(2-mercaptopropionyl)-glycine and catalase-treated piglets (*p < 0.05 vs no treatment). This study confirms the occurrence of hypoxemic/reoxygenation injury in immature hearts placed on cardiopulmonary bypass and shows that biochemical and functional damage can be counteracted by adding antioxidants to the cardiopulmonary bypass priming fluid. Contractile function improved in a dose-dependent manner, and oxygen-mediated damage could be avoided by mercaptopropionyl glycine/catalase treatment.(ABSTRACT TRUNCATED AT 400 WORDS)

Studies of hypoxemic/reoxygenation injury: without aortic clamping. IX. Importance of avoiding perioperative hyperoxemia in the setting of previous cyanosis

This study of an in vivo infantile piglet model of compensated hypoxemia tests the hypothesis that reoxygenation on hyperoxemic cardiopulmonary bypass produces oxygen-mediated myocardial injury that can be limited by normoxemic management of cardiopulmonary bypass and the interval after cardiopulmonary bypass. Twenty-five immature piglets (< 3 weeks old) were placed on 120 minutes of cardiopulmonary bypass and five piglets served as a biochemical control group without cardiopulmonary bypass. Five piglets underwent cardiopulmonary bypass without hypoxemia (cardiopulmonary bypass control). Twenty others became hypoxemic on cardiopulmonary bypass for 60 minutes by lowering oxygen tension to about 25 mm Hg. The study was terminated in five piglets at the end of hypoxemia, whereas 15 others were reoxygenated at an oxygen tension about 400 mm Hg or about 100 mm Hg for 60 minutes. Oxygen delivery was maintained during hypoxemia by increasing cardiopulmonary bypass flow and hematocrit level to avoid metabolic acidosis and lactate production. Myocardial function after cardiopulmonary bypass was evaluated from end-systolic elastance (conductance catheter) and Starling curve analysis. Myocardial conjugated diene production and creatine kinase leakage were assessed as biochemical markers of injury, and antioxidant reserve capacity was determined by measuring malondialdehyde after cardiopulmonary bypass in myocardium incubated in the oxidant, t-butylhydroperoxide. Cardiopulmonary bypass without hypoxemia caused no oxidant or functional damage. Conversely, reoxygenation at an oxygen tension about 400 mm Hg raised myocardial conjugated diene level and creatine kinase production (CD: 3.5 +/- 0.7 A233 nm/min/100 g, creatine kinase: 8.5 +/- 1.5 U/min/100 g, p < 0.05 vs cardiopulmonary bypass control), reduced antioxidant reserve capacity (malondialdehyde: 1115 +/- 60 nmol/g protein at 4.0 mmol t-butylhydroperoxide, p < 0.05 vs control), and produced severe postbypass dysfunction (end-systolic elastance recovered only 39% +/- 7%, p < 0.05 vs cardiopulmonary bypass control). Lowering oxygen tension to about 100 mm Hg during reoxygenation avoided conjugated diene production and creatine kinase release, retained normal antioxidant reserve, and improved functional recovery (80% +/- 11%, p < 0.05 vs oxygen tension about 400 mm Hg). These findings show that conventional hyperoxemic cardiopulmonary bypass causes unintended reoxygenation injury in hypoxemic immature hearts that may contribute to myocardial dysfunction after cardiopulmonary bypass and that normoxemic management may be used to surgical advantage.

Studies of hypoxemic/reoxygenation injury: without aortic clamping. III. Comparison of the magnitude of damage by hypoxemia/reoxygenation versus ischemia/reperfusion

The immature heart is more tolerant to ischemia than the adult heart, yet infants with cyanosis show myocardial damage after surgical correction of congenital cardiac defects causing hypoxemia. This study tested the hypothesis that the hypoxemic developing heart is susceptible to oxygen-mediated damage when it is reoxygenated during cardiopulmonary bypass and that this hypoxemic/reoxygenation injury is more severe than ischemic/reperfusion stress. Fifteen Duroc-Yorkshire piglets (2 to 3 weeks old, 3 to 5 kg) underwent 60 minutes of 37 degrees C cardiopulmonary bypass. Five piglets (control) were not made ischemic or hypoxemic. Five underwent 30 minutes of normothermic ischemia (aortic clamping) and 25 minutes of reperfusion before cardiopulmonary bypass was discontinued. Five others underwent 30 minutes of hypoxemia (bypass circuit primed with blood with oxygen tension 20 to 30 mm Hg) and 30 minutes of reoxygenation during cardiopulmonary bypass. Functional (left-ventricular contractility) and biochemical (levels of plasma and tissue conjugated dienes and antioxidant reserve capacity) measurements were made before ischemia/hypoxemia and after reperfusion/reoxygenation. Cardiopulmonary bypass (no ischemia or hypoxemia) caused no changes in left-ventricular function or coronary sinus levels of conjugated dienes. The tolerance to normothermic ischemia was confirmed, inasmuch as left-ventricular function returned to 108% of control values and coronary sinus levels of conjugated dienes did not rise after reperfusion. Conversely, reoxygenation raised plasma levels of conjugated dienes in coronary sinus blood in the hypoxic group 57% compared with end-hypoxic levels (p < 0.05 versus end-hypoxic levels and versus ischemia, by analysis of variance). Antioxidant reserve capacity showed the lowest levels (highest production of malondialdehyde) in the hypoxemic group (51% higher than control values; p < 0.05 by analysis of variance). These biochemical changes were associated with a 62% depression of left-ventricular function after bypass because end-systolic elastance recovered only 38% of control levels (p < 0.05 by analysis of variance). These data confirm the tolerance of the immature heart to ischemia and reperfusion and document a hypoxemic/reoxygenation injury that occurs in immature hearts reoxygenated during bypass. Hypoxemia seems to render the developing heart susceptible to reoxygenation damage that depresses postbypass function and is associated with lipid peroxidation. These findings suggest that starting bypass in cyanotic immature subjects causes an unintended reoxygenation injury that may potentially be counteracted by adding antioxidants to the prime of the extracorporeal circuit.

Studies of hypoxemic/reoxygenation injury: with aortic clamping. XIII. Interaction between oxygen tension and cardioplegic composition in limiting nitric oxide production and oxidant damage

This study tests the interaction between oxygen tension and cardioplegic composition on nitric oxide production and oxidant damage during reoxygenation of previously cyanotic hearts. Of 35 Duroc-Yorkshire piglets (2 to 3 weeks, 3 to 5 kg), six underwent 30 minutes of blood cardioplegic arrest with hyperoxemic (oxygen tension about 400 mm Hg), hypocalcemic, alkalotic, glutamate/aspartate blood cardioplegic solution during 1 hour of cardiopulmonary bypass without hypoxemia (control). Twenty-nine others were subjected to up to 120 minutes of ventilator hypoxemia (oxygen tension about 25 mm Hg) before reoxygenation on CPB. To simulate routine clinical management, nine piglets underwent uncontrolled cardiac reoxygenation, whereby cardiopulmonary bypass was started at oxygen tension of about 400 mm Hg followed by the aforementioned blood cardioplegic protocol 5 minutes later. All 20 other piglets underwent controlled cardiac reoxygenation, whereby cardiopulmonary bypass was started at the ambient oxygen tension (about 25 mm Hg), and reoxygenation was delayed until blood cardioplegia was given. The blood cardioplegia solution was kept normoxemic (oxygen tension about 100 mm Hg) in 10 piglets and made hyperoxemic (oxygen tension about 400 mm Hg) in 10 others. The cardioplegic composition was also varied so that the cardioplegic solution in each subgroup contained either KCl only (30 mEq/L) or components that theoretically inhibit nitric oxide synthase by including hypocalcemia, alkalosis, and glutamate/aspartate. Function (end-systolic elastance) and myocardial nitric oxide production, conjugated diene production, and antioxidant reserve capacity were measured. Blood cardioplegic arrest without hypoxemia did not cause myocardial nitric oxide or conjugated diene production, reduce antioxidant reserve capacity, or change left ventricular functional recovery. In contrast, uncontrolled cardiac reoxygenation raised nitric oxide and conjugated diene production 19- and 13-fold, respectively (p < 0.05 vs control), reduced antioxidant reserve capacity 40%, and contractility recovered only 21% of control levels. After controlled cardiac reoxygenation at oxygen tension about 400 mm Hg with cardioplegic solution containing KCl only, nitric oxide and conjugated diene production rose 16- and 12-fold, respectively (p < 0.05 vs control), and contractility recovered only 43% +/- 5%. Normoxemic (oxygen tension of about 100 mm Hg) controlled cardiac reoxygenation with the same solution reduced nitric oxide and conjugated diene production 85% and 71%, and contractile recovery rose to 55% +/- 7% (p < 0.05 vs uncontrolled reoxygenation). In comparison, controlled cardiac reoxygenation with an oxygen tension of about 400 mm Hg hypocalcemic, alkalotic, glutamate/aspartate blood cardioplegic solution reduced nitric oxide and conjugated diene production 85% and 62%, respectively, and contractility recovered 63% +/- 4% (p < 0.05 vs KCl only).(ABSTRACT TRUNCATED AT 400 WORDS)

Studies of hypoxemic/reoxygenation injury with aortic clamping: XI. Cardiac advantages of normoxemic versus hyperoxemic management during qardiopulmonary bypass

The conventional way to start cardiopulmonary bypass is to prime the cardiopulmonary bypass circuit with hyperoxemic blood (oxygen tension about 400 mm Hg) and deliver cardioplegic solutions at similar oxygen tension levels. This study tests the hypothesis that an initial normoxemic oxygen tension strategy to decrease the oxygen tension-dependent rate of oxygen free radical production will, in concert with normoxemic blood cardioplegia, limit reoxygenation damage and make subsequent hyperoxemia (oxygen tension about 400 mm Hg) safer. Thirty-five immature (3 to 5 kg, 2 to 3 week old) piglets underwent 60 minutes of cardiopulmonary bypass. Eleven control studies at conventional hyperoxemic oxygen tension (about 400 mm Hg) included six piglets that also underwent 30 minutes of blood cardioplegic arrest. Of 25 studies in which piglets were subjected to up to 120 minutes of ventilator hypoxemia (reducing fraction of inspired oxygen to 5% to 7%; oxygen tension about 25 mm Hg), 11 underwent either abrupt (oxygen tension about 400 mm Hg, n = 6) or gradual (increasing oxygen tension from 100 to 400 mm Hg over a 1-hour period, n = 5) reoxygenation without blood cardioplegia. Fourteen others underwent 30 minutes of blood cardioplegic arrest during cardiopulmonary bypass. Of these, nine were reoxygenated at oxygen tension about 400 mm Hg, and five others underwent normoxemic cardiopulmonary bypass and blood cardioplegia (oxygen tension about 100 mm Hg) with systemic oxygen tension raised to 400 mm Hg after aortic unclamping. Measurements of lipid peroxidation (conjugated dienes and antioxidant reserve capacity) and contractile function (pressure-volume loops, conductance catheter, end-systolic elastance) were made before and during hypoxemia and 30 minutes after reoxygenation. Hyperoxemic cardiopulmonary bypass did not produce oxidant damage or reduce functional recovery after cardiopulmonary bypass in nonhypoxemic controls. In contrast, abrupt and gradual reoxygenation without blood cardioplegia produced significant lipid peroxidation (84% increase in conjungated dienes), lowered antioxidant reserve capacity 68% +/- 5%, 44% +/- 8%, respectively, and decreased functional recovery 75% +/- 6% (p < 0.05), 66% +/- 4% (p < 0.05). Similar impairment followed abrupt reoxygenation before blood cardioplegic myocardial management, because conjungated diene production increased 13-fold, antioxidant reserve capacity fell 40%, and contractility recovered only 21% +/- 2% (p < 0.05). Conversely, normoxemic induction of cardiopulmonary bypass and blood cardioplegic myocardial management reduced conjungated diene production 73%, avoided impairment of antioxidant reserve capacity, and resulted in 58% +/- 11% recovery of contractile function.(ABSTRACT TRUNCATED AT 400 WORDS)

Studies of hypoxemic/reoxygenation injury: without aortic clamping. IV. Role of the iron-catalyzed pathway: deferoxamine

This study tests the hypothesis that an iron chelator, deferoxamine, can reduce oxygen-mediated myocardial injury and avoid myocardial dysfunction after cardiopulmonary bypass by its action on the iron-catalyzed Haber-Weiss pathway. Twenty-one immature 2- to 3-week-old piglets were placed on cardiopulmonary bypass for 120 minutes, and five piglets served as biochemical controls without cardiopulmonary bypass. Five piglets underwent cardiopulmonary bypass without hypoxemia (cardiopulmonary bypass control). Sixteen others became hypoxemic while undergoing cardiopulmonary bypass for 60 minutes by lowering oxygen tension to about 25 mm Hg, followed by reoxygenation at oxygen tension about 400 mm Hg for 60 minutes. Oxygen delivery was maintained during hypoxemia by increasing cardiopulmonary bypass flow and hematocrit level. In seven piglets deferoxamine (50 mg/kg total dose) was given both intravenously just before reoxygenation and by a bolus injection (5 mg/kg) into the cardiopulmonary bypass circuit; nine others were not treated (no therapy). Myocardial function after cardiopulmonary bypass was evaluated form end-systolic elastance (conductance catheter) and Starling curve analysis. Myocardial conjugated diene production and creatine kinase leakage were assessed as biochemical markers of injury, and antioxidant reserve capacity was determined by measuring malondialdehyde in postcardiopulmonary bypass myocardium incubated in the oxidant, t-butylhydroperoxide. Cardiopulmonary bypass without hypoxemia caused no oxidant or functional damage. Conversely, reoxygenation (no therapy) raised myocardial conjugated diene levels and creatine kinase production (conjugated diene: 3.5 +/- 0.7 absorbance 233 nm/min/100 g, creatine kinase: 8.5 +/- 1.5 U/min/100 g; p < 0.05 versus cardiopulmonary bypass control), reduced antioxidant reserve capacity (malondialdehyde: 1115 +/- 60 nmol/g protein at 4 mmol/L t-butylhydroperoxide; p < 0.05 versus control), and produced severe post-bypass dysfunction (end-systolic elastance recovered only 39% +/- 7%, p < 0.05 versus cardiopulmonary bypass control). Deferoxamine avoided conjugated diene production and creatine kinase release and retained normal antioxidant reserve, and functional recovery was complete (95% +/- 11%, p < 0.05 versus no treatment). These findings show that iron-catalyzed oxidants may contribute to a reoxygenation injury and imply that deferoxamine may be used to surgical advantage.

Studies of hypoxemic/reoxygenation injury: without aortic clamping. VII. Counteraction of oxidant damage by exogenous antioxidants: coenzyme Q10

Coenzyme Q10 (CoQ10) is a natural mitochondrial respiratory chain constituent with antioxidant properties. This study tests the hypothesis that CoQ10 administered before the onset of reoxygenation on cardiopulmonary bypass, can reduce oxygen-mediated myocardial injury and avoid myocardial dysfunction after cardiopulmonary bypass. The antioxidant properties of CoQ10 were confirmed by an in vitro study in which normal myocardial homogenates were incubated with the oxidant, t-butylhydroperoxide. Fifteen immature piglets (< 3 weeks old) were placed on 60 minutes of cardiopulmonary bypass. Five piglets underwent cardiopulmonary bypass without hypoxemia (oxygen tension about 400 mm Hg). Ten others became hypoxemic on cardiopulmonary bypass for 30 minutes by lowering oxygen tension to approximately 25 mm Hg, followed by reoxygenation at oxygen tension about 400 mm Hg for 30 minutes. In five piglets, CoQ10 (45 mg/kg) was added to the cardiopulmonary bypass circuit 15 minutes before reoxygenation, and five others were not treated (no treatment). Myocardial function after cardiopulmonary bypass was evaluated from end-systolic elastance (conductance catheter), oxidant damage (lipid peroxidation) was assessed by measuring conjugated diene levels in coronary sinus blood, and antioxidant reserve capacity was determined by measuring malondialdehyde in myocardium after cardiopulmonary bypass incubated in the oxidant, t-butylhydroperoxide. Cardiopulmonary bypass without hypoxemia caused no oxidant damage and allowed complete functional recovery. Reoxygenated hearts (no treatment) showed a progressive increase in conjugated diene levels in coronary sinus blood after reoxygenation (2.3 +/- 0.6 A233 nm/0.5 ml plasma at 30 minutes after reoxygenation) and reduced antioxidant reserve capacity (malondialdehyde: 1219 +/- 157 nmol/g protein at 4.0 mmol/L t-butylhydroperoxide), resulting in severe postbypass dysfunction (percent end-systolic elastance = 38 +/- 6). Conversely, CoQ10 treatment avoided the increase in conjugated diene levels (2.1 +/- 0.6 vs 1.1 +/- 0.3, p < 0.05 vs no treatment), retained normal antioxidant reserve (896 +/- 76 nmol/g protein, p < 0.05 vs no treatment), and allowed nearly complete recovery of function (94% +/- 7%, p < 0.05 vs no treatment). We conclude that reoxygenation of the hypoxemic immature heart on cardiopulmonary bypass causes oxygen-mediated myocardial injury, which can be limited by CoQ10 treatment before reoxygenation. These findings imply that coenzyme Q10 can be used to surgical advantage in cyanotic patients, because therapeutic blood levels can be achieved by preoperative oral administration of this approved drug.

Studies of hypoxemic/reoxygenation injury: without aortic clamping. II. Evidence for reoxygenation damage

This study tested the hypothesis that the developing heart is susceptible to oxygen-mediated damage after reintroduction of molecular oxygen and that this "unintended" reoxygenation injury causes lipid peroxidation and functional depression that may contribute to perioperative cardiac dysfunction. Among 49 Duroc-Yorkshire piglets (2 to 3 weeks old, 3 to 5 kg) 15 control studies were done without hypoxemia to test the effects of the surgical preparation (n = 10) and 60 minutes of cardiopulmonary bypass (n = 5). Twenty-nine piglets underwent up to 2 hours of ventilator hypoxemia (with inspired oxygen fraction reduced to 6% to 7%) to lower arterial oxygen tension to approximately 25 mm Hg. Five piglets did not undergo reoxygenation to determine alterations caused by hypoxemia alone. Twenty-four others received reoxygenation by either raising ventilator inspired oxygen fraction to 1.0 (n = 12) or instituting cardiopulmonary bypass at oxygen tension 400 mm Hg (n = 12). Ventilator hypoxemia produced sufficient hemodynamic compromise and metabolic acidosis that 18 piglets required premature reoxygenation (78 +/- 12 minutes). To avoid the influence of acidosis and hemodynamic deterioration during ventilator hypoxemia, five others underwent 30 minutes of hypoxemia during cardiopulmonary bypass (circuit primed with blood at oxygen tension 25 mm Hg) and 30 minutes of reoxygenation (oxygen tension 400 mm Hg) during cardiopulmonary bypass. Biochemical markers of oxidant damage included measurement of coronary sinus and myocardial conjugated dienes to determine lipid peroxidation and antioxidant reserve capacity assessed by incubating myocardial tissue in the oxidant t-butylhydroperoxide. Functional recovery was determined by inscribing pressure volume loops to determine end-systolic elastance and Starling curves by volume infusion. No biochemical or functional changes occurred in control piglets. Hypoxemia without reoxygenation did not change plasma levels of conjugated dienes, but lowered antioxidant reserve capacity 24%. Reoxygenation by ventilator caused refractory ventricular arrhythmias in two piglets (17% mortality), raised levels of conjugated dienes 45%, and reduced antioxidant reserve capacity 40% with recovery of 39% of mechanical function in the survivors. Comparable biochemical and functional changes occurred in piglets undergoing ventilator hypoxemia and/or cardiopulmonary bypass hypoxemia and reoxygenation on cardiopulmonary bypass. We conclude that hypoxemia increases vulnerability to reoxygenation damage by reducing antioxidant reserve capacity and that reoxygenation by either ventilator or cardiopulmonary bypass produces oxidant damage with resultant functional depression that is not a result of cardiopulmonary bypass. These findings suggest that initiation of cardiopulmonary bypass in cyanotic immature subjects causes an unintended reoxygenation injury, which may increase vulnerability to subsequent ischemia during surgical repair.

Studies of hypoxemic/reoxygenation injury: without aortic clamping. V. Role of the L-arginine-nitric oxide pathway: the nitric oxide paradox

This study tests the hypothesis that nitric oxide, which is endothelial-derived relaxing factor, produces reoxygenation injury via the L-arginine-nitric oxide pathway in hypoxemic immature hearts when they are placed on cardiopulmonary bypass. Twenty 3-week-old piglets undergoing 2 hours of hypoxemia (oxygen tension about 25 mm Hg) on a ventilator were reoxygenated by initiating cardiopulmonary bypass (oxygen tension about 400 mm Hg). Five animals were not treated, whereas the pump circuit was primed with the nitric oxide-synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME, 4 mg/kg) in five piglets. L-Arginine, the substrate for nitric oxide, was administered in a fivefold excess (20 mg/kg), together with L-NAME in five piglets (L-NAME and L-arginine), and given alone in five other piglets (L-arginine). Five normoxemic, instrumented piglets served as a control group, and five others underwent 30 minutes of cardiopulmonary bypass without preceding hypoxemia. Left ventricular contractility was determined as end-systolic elastance by pressure-dimension loops. Myocardial conjugated dienes were measured as a marker of lipid peroxidation, and the antioxidant reserve capacity (malondialdehyde production in tissue incubated with t-butylhydroperoxide) was measured. Nitric oxide level was determined in coronary sinus plasma as its spontaneous oxidation product, nitrite. Cardiopulmonary bypass per se did not alter left ventricular contractility, cause lipid peroxidation, or lower antioxidant capacity. Reoxygenation without treatment depressed cardiac contractility (end-systolic elastance 38% +/- 12% of control*), raised nitric oxide (127% above hypoxemic values), increased conjugated dienes (1.3 +/- 0.2 vs 0.7 +/- 0.1, control*), and reduced antioxidant reserve capacity (910 +/- 59 vs 471 +/- 30, control*). Inhibition of nitric oxide production by L-NAME improved end-systolic elastance to 84% +/- 12%,** limited conjugated diene elution (0.8 +/- 0.1 vs 1.3 +/- 0.2, no treatment**), and improved antioxidant reserve capacity (679 +/- 69 vs 910 +/- 59, no treatment**). Conversely, L-arginine counteracted these beneficial effects of L-NAME, because left ventricular function recovered only 24% +/- 6%,* conjugated dienes were 1.2 +/- 0.1,* and antioxidant reserve capacity was 826 +/- 70.* L-Arginine alone caused the same deleterious biochemical changes as L-NAME/L-arginine and resulted in 60% mortality. The close relationship between postbypass left ventricular dysfunction (percent end-systolic elastance) and myocardial conjugated diene production (r = 0.752) provides in vivo evidence that lipid peroxidation contributes to myocardial dysfunction after reoxygenation.(ABSTRACT TRUNCATED AT 400 WORDS)

Studies of hypoxemic/reoxygenation injury: without aortic clamping. VIII. Counteraction of oxidant damage by exogenous glutamate and aspartate

Previous studies show that (1) hypoxemia depletes immature myocardium of amino acid substrates and their replenishment improves ischemic tolerance, (2) reoxygenation on cardiopulmonary bypass causes oxygen-mediated damage without added ischemia, and (3) this damage may be related to the nitric oxide-L-arginine pathway that is affected by amino acid metabolism. This study tests the hypothesis that priming the cardiopulmonary bypass circuit with glutamate and aspartate limits reoxygenation damage. Of 22 immature Duroc-Yorkshire piglets (< 3 weeks old), five were observed over a 5-hour period (control), and five others underwent 30 minutes of CPB without hypoxemia (cardiopulmonary bypass control). Twelve others became hypoxemic by reducing ventilator inspired oxygen fraction to 6% to 7% (oxygen tension about 25 mm Hg) before reoxygenation on cardiopulmonary bypass for 30 minutes. Of these five were untreated (no treatment), and the cardiopulmonary bypass circuit was primed with 5 mmol/L glutamate and aspartate in seven others (treatment). Left ventricular function before and after bypass was measured by inscribing pressure-volume loops (end-systolic elastance). Myocardial conjugated diene levels were measured to detect lipid peroxidation, and antioxidant reserve capacity was tested by incubating cardiac muscle with the oxidant t-butylhydroperoxide to determine the susceptibility to subsequent oxidant injury. CPB (no hypoxemia) allowed complete functional recovery without changing conjugated dienes and antioxidant reserve capacity, whereas reoxygenation injury developed in untreated hearts. This was characterized by reduced contractility (elastance end-systolic recovered only 37% +/- 8%*), increased conjugated diene levels (1.3 +/- 0.1 vs 0.7 +/- 0.1*), and decreased antioxidant reserve capacity (910 +/- 59 vs 471 +/- 30 malondialdehyde nmol/g protein at 2 mmol/L t-butylhydroperoxide*). In contrast, priming the cardiopulmonary bypass circuit with glutamate and aspartate resulted in significantly better left ventricular functional recovery (75% +/- 8% vs 37% +/- 8%*), minimal conjugated diene production (0.8 +/- 0.1 vs 1.3 +/- 0.1*), and improved antioxidant reserve capacity (726 +/- 27 vs 910 +/- 59 malondialdehyde nmol/g protein*) (*p < 0.05 vs cardiopulmonary bypass control). We conclude that reoxygenation of immature hypoxemic piglets by the initiation of cardiopulmonary bypass causes myocardial dysfunction, lipid peroxidation, and reduced tolerance to oxidant stress, which may increase vulnerability to subsequent ischemia (i.e., aortic crossclamping). These data suggest that supplementing the prime of cardiopulmonary bypass circuit with glutamate and aspartate may reduce these deleterious consequences of reoxygenation.

Studies of hypoxemic/reoxygenation injury: with aortic clamping. X. Exogenous antioxidants to avoid nullification of the cardioprotective effects of blood cardioplegia

This study tests the hypothesis that reoxygenation of cyanotic immature hearts when starting cardiopulmonary bypass produces an "unintended" reoxygenation injury that (1) nullifies the cardioprotective effects of blood cardioplegia and (2) is avoidable by adding antioxidants N-(2-mercaptopropionyl)-glycine plus catalase to the cardiopulmonary bypass prime. Twenty immature piglets (2 to 3 weeks) underwent 30 minutes of aortic clamping with a blood cardioplegic solution that was hypocalcemic, alkalotic, hyperosmolar, and enriched with glutamate and aspartate during 1 hour of cardiopulmonary bypass. Of these, six piglets did not undergo hypoxemia (blood cardioplegic control) and 14 others remained hypoxemic (oxygen tension about 25 mm Hg) for up to 2 hours by lowering ventilator fraction of inspired oxygen before reoxygenation on cardiopulmonary bypass. The primary solution of the cardiopulmonary bypass circuit was unchanged in eight piglets (no treatment) and supplemented with the antioxidants N-(2-mercaptopropionyl)-glycine (80 mg/kg) and catalase (5 mg/kg) in six others (N-(2-mercaptopropionyl)-glycine and catalase). Myocardial function (end-systolic elastance), lipid peroxidation (myocardial conjugated diene production), and antioxidant reserve capacity were evaluated. Blood cardioplegic arrest produced no biochemical or functional changes in nonhypoxemic control piglets. Reoxygenation caused an approximate 10-fold increase in conjugated production that persisted throughout cardiopulmonary bypass, lowered antioxidant reserve capacity 86% +/- 12%, and produced profound myocardial dysfunction, because end-systolic elastance recovered only 21% +/- 2%. Supplementation of the cardiopulmonary bypass prime with N-(2-mercaptopropionyl)-glycine and catalase reduced lipid peroxidation, restored antioxidant reserve capacity, and allowed near complete functional recovery (80% +/- 8%).** Lipid peroxidation (conjugated diene) production was lower during warm blood cardioplegic reperfusion than during induction in all reoxygenated hearts, which suggests that blood cardioplegia did not injure reoxygenated myocardium. We conclude that reoxygenation of the hypoxemic immature heart causes cardiac functional and antioxidant damage that nullifies the cardioprotective effects of blood cardioplegia that can be avoided by supplementation of the cardiopulmonary bypass prime with antioxidants (*p < 0.05 vs blood cardioplegic control; **p < 0.05 vs reoxygenation).

Studies of hypoxemic/reoxygenation injury: with aortic clamping. XII. Delay of cardiac reoxygenation damage in the presence of cyanosis: a new concept of controlled cardiac reoxygenation

Twenty-one immature piglets (< 3 weeks old) underwent 30 minutes of aortic clamping with hypocalcemic glutamate/aspartate blood cardioplegia. Six piglets underwent hyperoxemic cardiopulmonary bypass and blood cardioplegia without preceding hypoxemia (control). Fifteen piglets became hypoxemic (oxygen tension about 25 mm Hg) for up to 2 hours by decreasing ventilator fraction of inspired oxygen to 6% to 7% before cardiopulmonary bypass. Of these, six piglets underwent 5 minutes of abrupt hyperoxemic uncontrolled reoxygenation by starting cardiopulmonary bypass at oxygen tension of about 400 mm Hg before they received oxygen tension of about 400 mm Hg blood cardioplegia. Nine others underwent controlled cardiac reoxygenation by starting cardiopulmonary bypass at ambient oxygen tension (about 25 mm Hg) followed 5 minutes later by 30 minutes of cardiopulmonary bypass at normoxemic oxygen tension (about 100 mm Hg) before raising oxygen tension to about 400 mm Hg. Myocardial function after cardiopulmonary bypass was evaluated from end-systolic elastance by conductance catheter, oxidant damage was estimated by measuring transcoronary conjugated diene levels to detect lipid peroxidation, and antioxidant reserve capacity was determined by measuring malondialdehyde produced from myocardium incubated with the oxidant t-butylhydroperoxide. Hyperoxemic cardiopulmonary bypass and blood cardioplegia preserved myocardial function and produced no oxidant damage in nonhypoxemic piglets. In contrast, uncontrolled reoxygenation at oxygen tension about 400 mm Hg, followed by blood cardioplegia, resulted in marked conjugated dienes production (42 +/- 4* vs 3 +/- 1) A233 nm/min/100 g during blood cardioplegic induction, reduced antioxidant reserve capacity malondialdehyde at 4 mmol/L t-butylhydroperoxide; 1342 +/- 59* vs 958 +/- 50 nmol/g protein) and caused profound myocardial dysfunction; end-systolic elastance recovered only 21% +/- 2%* despite a blood cardioplegic regimen that was cardioprotective in nonhypoxemic piglets. Conversely, controlled cardiac reoxygenation reduced lipid peroxidation (conjugated dienes production was 2 +/- 1**), restored antioxidant reserve capacity (malondialdehyde at 4 mmol/L t-butylhydroperoxide; 982 +/- 88**), and allowed near-complete (83 +/- 8%**) functional recovery. We conclude that reoxygenation of the hypoxemic immature heart by initiating conventional hyperoxemic cardiopulmonary bypass causes oxidant damage characterized by lipid peroxidation, reduced antioxidant reserve capacity, and results in functional depression that nullifies the cardioprotective effects of blood cardioplegia. These changes can be reduced by starting cardiopulmonary bypass at the ambient oxygen tension of the hypoxemic subject and delaying subsequent reoxygenation until blood cardioplegic induction by controlled cardiac reoxygenation (*p < 0.05 vs control; **p < 0.05 vs uncontrol reoxygenation) and analysis of variance.

Reduction of reoxygenation injury and nitric oxide production in the cyanotic immature heart by controlling pO2

Reintroduction of high levels of molecular oxygen after a hypoxic period is followed by a burst of nitric oxide (NO), peroxynitrite, and oxygen free radicals, which are highly cytotoxic. This study tests the hypotheses that a) controlled reoxygenation of cyanotic immature hearts when starting cardiopulmonary bypass (CPB) with high pO2 pressure of oxygen produces a reoxygenation injury, and b) this oxygen-related damage is avoidable by controlling the circumstances of the reoxygenation period (controlled reoxygenation). Of 40 immature piglets (2-3 weeks), 5 normoxic instrumented piglets served as control, and 6 underwent 1 h of CPB including 30 min of aortic clamping with blood cardioplegic (BCP) arrest without preceding hypoxia (BCP control). Twenty-nine others were made hypoxic (arterial pO2 20-30 mmHg) for up to 2 h by lowering the forced inspiratory oxygen (FiO2) on a ventilator. They were then reoxygenated on CPB as follows, 1) abrupt reoxygenation at pO2 400 mmHg in 5, (Reox), 2) gradual increase in pO2 from 30 to 400 mmHg in 5 (Graded Reox), both without BCP arrest, 3) starting CPB at different pO2 levels (hyperoxic, normoxic or hypoxic) for 5 min, followed by BCP arrest (Reox+BCP: pO2 > 400, 100 or 20-30 mmHg), in 19 others. Reoxygenation on CPB at pO2 more than 400 mmHg depressed contractility (endsystolic elastance [Ees] to 25 +/- 5% of control; P < 0.05), accompanied by reduced antioxidant reserve capacity [AORC] (P < 0.05 vs control), which was only slightly improved by Graded Reox (Ees 34 +/- 4%, P < 0.05 vs control).(ABSTRACT TRUNCATED AT 250 WORDS)

Reperfusion injury in skeletal muscle: controlled limb reperfusion reduces local and systemic complications after prolonged ischaemia

Previous studies in isolated limbs using crystalloid perfusion solutions have shown that control of the initial reperfusion reduces postischaemic complications. However, no experimental study has been undertaken to evaluate the concept of controlled limb reperfusion experimentally in an in vivo blood-perfused model and to assess the local as well as systemic effects of normal blood reperfusion and controlled limb reperfusion. Of 20 pigs undergoing preparation of the infrarenal aorta and iliac arteries, six were observed for 7.5 h and served as controls; 14 others underwent 6 h of complete infrarenal occlusion. Thereafter, embolectomy was simulated in eight pigs by removing the aortic clamp and establishing normal blood reperfusion at systemic pressure. In six other pigs, the composition of the reperfusate and the conditions of reperfusion were controlled during the first 30 min, followed by normal blood reperfusion. Some 6 h of infrarenal aortic occlusion leads to a severe decrease in high-energy phosphates and muscle temperature, together with a slight increase in creatine kinase and potassium in the systemic circulation. Normal blood reperfusion resulted in severe reperfusion injury: massive oedema developed, the tissue showed a marked decrease in oxygen consumption, glucose consumption, tissue ATP, total adenine nucleotides, muscle pH and total calcium in the femoral vein. Furthermore, a massive increase was seen in plasma creatine kinase concentration and potassium, together with the development of muscle rigidity. In sharp contrast, initial treatment of the ischaemic skeletal muscle by controlled limb reperfusion resulted in normal water content, oxygen consumption, glucose consumption, flow and muscle rigidity. Furthermore, controlled limb reperfusion resulted in higher total adenine nucleotides content, less tissue acidosis, markedly reduced creatine kinase release, and potassium release as compared with that of normal blood reperfusion. This study shows that 6 h of acute infrarenal aortic occlusion will result in severe reperfusion injury (postischaemic syndrome) if normal blood at systemic pressure is given in the initial reperfusion phase. In contrast, initial treatment of the ischaemic skeletal muscle by controlled limb reperfusion reduces the metabolic, functional and biochemical alterations.

Simultaneous arterial and coronary sinus cardioplegic perfusion: an experimental and clinical study

The existence of inhomogeneous distribution of coronary flow with antegrade or retrograde perfusion alone has led to alternating between these delivery routes to maximize their individual benefits. Concern over myocardial damage prevented the simultaneous application of antegrade and retrograde cardioplegic blood delivery. Based upon the predominance of retrograde drainage via Thebesian veins, and evidence that pressure-controlled intermittent coronary sinus occlusion during antegrade cardioplegic delivery enhances its distribution and protective properties, this study tests (a) the hypothesis that simultaneous aortic and coronary sinus perfusion is safe during aortic clamping, and (b) reports initial clinical application of this combined strategy in 174 patients. Five minipigs (25-30 kg) underwent 1 hr of aortic clamping with simultaneous aortic (antegrade) and coronary sinus (retrograde) perfusion at 200 ml/min with normal blood (37 degrees C) before and after 30 minutes of perfusion with either warm (37 degrees C) or cold (4 degrees C) blood cardioplegia (BCP). Furthermore, the combined strategy was used in 174 high-risk patients (NYHA class III-IV) at 3 university hospitals to perform myocardial protection during CABG or valve replacement, or a combination of both. Included were 16 patients in cardiogenic shock and 24 undergoing reoperation. In both the clinical and the experimental studies the coronary sinus pressure was always < 40 mmHg in beating or arrested hearts.

EXPERIMENTAL

Compared to control values (81.4 +/- 0.4% tissue water content), no right-ventricular (80.8 +/- 0.8%) or left-ventricular (79.5 +/- 0.3%) edema developed, no lactate was produced (control: -1.0 +/- 0.5 mg/100 g/min, empty beating: -0.64 +/- 5, and BCP arrest: -8.6 +/- 6.6).(ABSTRACT TRUNCATED AT 250 WORDS)

Role of controlled cardiac reoxygenation in reducing nitric oxide production and cardiac oxidant damage in cyanotic infantile hearts

Cardiopulmonary bypass (CPB) is used increasingly to correct cyanotic heart defects during early infancy, but myocardial dysfunction is often seen after surgical repair. This study evaluates whether starting CPB at a conventional, hyperoxic pO2 causes an "unintentional" reoxygenation (ReO2) injury. We subjected 2-wk-old piglets to ventilator hypoxemia (FIO2 approximately 0.06, pO2 approximately 25 mmHg) followed by 5 min of ReO2 on CPB before instituting cardioplegia. CPB was begun in hypoxemic piglets by either abrupt ReO2 at a pO2 of 400 mmHg (standard clinical practice) or by maintaining pO2 approximately 25 mmHg on CPB until controlling ReO2 with blood cardioplegic arrest. The effects of abrupt vs. gradual ReO2 without surgical ischemia (blood cardioplegia) were also compared. Myocardial nitric oxide (NO) production (chemiluminescence measurements of NO2- + NO3-) and conjugated diene (CD) generation (spectrophotometric A233 measurements of lipid extracts) using aortic and coronary sinus blood samples were assessed during cardioplegic induction. 30 min after CPB, left ventricular end-systolic elastance (Ees, catheter conductance method) was used to determine cardiac function. CPB and blood cardioplegic arrest caused no functional or biochemical change in normoxic (control) hearts. Abrupt ReO2 caused a depression of myocardial function (Ees = 25 +/- 5% of control). Functional depression was relatively unaffected by gradual ReO2 without blood cardioplegia (34% recovery of Ees), and abrupt ReO2 immediately before blood cardioplegia caused a 10-fold rise in cardiac NO and CD production, with subsequent depression of myocardial function (Ees 21 +/- 2% of control). In contrast, controlled cardiac ReO2 reduced NO production 94%, CD did not rise, and Ees was 83 +/- 8% of normal. We conclude ReO2 injury is related to increased NO production during abrupt ReO2, nullifies the cardioprotective effects of blood cardioplegia, and that controlled cardiac ReO2 when starting CPB to correct cyanotic heart defects may reduce NO production and improve myocardial status postoperatively.

New approaches to blood cardioplegic delivery to reduce hemodilution and cardioplegic overdose

These studies present modifications of the cardioplegic components of a standard cardioplegic formulation, delivered previously at 4:1, to allow an 8:1 blood:cardioplegic mixture, thereby limiting hemodilution. Data are included to show that the hyperkalemic (20 mEq/L) glutamate/aspartate enriched solution used previously for warm induction can be used also for warm reperfusion (instead of the 10 mEq/L KCl solution), thereby avoiding the need to formulate two different solutions that vary only in potassium concentration. Studies of cold (4 degrees C) retrograde noncardioplegic blood infusion after arrest with hyperkalemic blood cardioplegia document the safety of maintaining arrest with continuous retrograde infusion of cold normokalemic blood, thereby indicating that ischemia and cardioplegia are unnecessary during aspects of cardiac operations where perfusion does not impair visualization (i.e., construction of proximal anastomoses). A new cardioplegic delivery system containing a shunt line is presented to expedite conversion from blood cardioplegia to blood infusion when continuous infusion is used.

New surgical treatment for severe limb ischemia

Revascularization after prolonged complete limb ischemia may result in severe damage to skeletal muscle and systemic alterations (postischemic syndrome). Our previous experimental studies have shown that this injury can be reduced substantially by treating the jeopardized extremity by controlling the conditions of reperfusion and composition of the initial reperfusate. In the present study this concept of controlled limb reperfusion was applied in patients with prolonged severe limb ischemia. Controlled limb reperfusion was used in 14 patients after prolonged complete uni- or bilateral ischemia. The ischemic interval ranged from 5 to 21 h. Two patients were in cardiogenic shock, 11 had associated cardiac disease, and seven coexistent peripheral vascular disease. After systemic heparinization, standard thromboembolectomy was done using a Fogarty catheter. Cannulas were placed into the iliac, profunda, and superficial femoral arteries and were connected to a reperfusion set. Oxygenated blood was drawn from the iliac artery and mixed with an asanguineous solution (ratio 6:1). This controlled reperfusate was delivered into the profunda and superficial femoral arteries using a single rollerpump. The system allows control of the composition of the reperfusate (calcium, pH, osmolarity, glucose, substrate, pO2, free radical scavengers) and the conditions of reperfusion (pressure, flow, temperature). After 30 min of controlled limb reperfusion, the cannulas were removed and normal blood reperfusion started. All 12 patients who were stable hemodynamically before the operation survived the revascularization. Eleven patients, including one with acute aortic occlusion for several hours, were discharged with functional recovery of their extremities. Despite the severe ischemic insult, controlled limb reperfusion avoided amputation and profound systemic complications. Two patients who were in cardiogenic shock preoperatively died from progressive cardiac failure. We conclude that controlled arterioarterial limb reperfusion may reduce the local manifestations of the postischemic syndrome after prolonged periods of ischemia, may salvage limbs thought previously to be damaged irreversibly by prolonged ischemia, and can be done easily in the operating room.

The safety of simultaneous arterial and coronary sinus perfusion: experimental background and initial clinical results

Concern over myocardial damage from simultaneous arterial (antegrade) and coronary sinus (retrograde) perfusion has led to alternating between these delivery routes to maximize their individual benefits. Based upon predominant retrograde drainage via Thebesian veins, this study: (1) confirms experimentally the safety of simultaneous arterial and coronary sinus perfusion; and (2) reports initial clinical application of this combined strategy in 155 consecutive patients.

EXPERIMENTAL

Five mini-pigs (25 to 30 kg) underwent 1 hour of aortic clamping with simultaneous aortic and coronary sinus perfusion at 200 mL/min with normal blood (37 degrees C) before and after 30 minutes of perfusion with either warm (37 degrees C) or cold (4 degrees C) blood cardioplegia. Coronary sinus pressure was always less than 30 mmHg. There was no right or left ventricular edema, lactate production, or lipid peroxidation as transmyocardial and myocardial conjugated dienes were unaltered, and postbypass recovered left ventricular end-systolic elastance (conductance catheter) and preload recruitable stroke work index 101% +/- 3% and 109% +/- 90%, respectively. CLINICAL: Simultaneous arterial/coronary sinus perfusion was used in 155 consecutive high risk patients (New York Heart Association Class III to IV) undergoing isolated coronary artery bypass grafting (CABG) (n = 109) and CABG+valve replacement/repair or aneurysm (n = 46). Included were 16 patients in cardiogenic shock and 24 undergoing reoperation. Mean aortic clamping time averaged 90 +/- 4 minutes (range 30 to 207), with 3.5 +/- 0.1 grafts per patient; all anastomoses were performed with the aorta clamped. Cold intermittent blood cardioplegia was used for distal anastomoses and valve implantation/repair in 123 patients, and warm continuous blood cardioplegia was used in 32 patients. Following a warm cardioplegic reperfusate, all patients received warm noncardioplegic blood perfusion simultaneously via grafts and coronary sinus. Coronary sinus pressure was always less than 40 mmHg. Of 18 patients requiring postoperative mechanical circulatory support (IABP), 16 had IABP placed preoperatively for cardiogenic shock. There were three postoperative myocardial infarctions (2%), and six patients died (3.9% mortality).

CONCLUSION

These experimental and clinical findings overcome perceived concerns about myocardial damage from simultaneous arterial and coronary sinus perfusion, and suggest this approach may add to the armamentarium of cardioprotective strategies.

High PAI activity with correlation to triglyceride and HDL cholesterol values in patients with coronary artery disease with no difference in survivors of myocardial infarction

The fibrinolytic capacity of blood depends mainly on the amount of tissue-type plasminogen activator (t-PA) activity and plasminogen activator inhibitor type-1 (PAI-1) activity. Previous studies linked high PAI activity or low t-PA activity with the development of atherosclerosis and thromboembolic diseases. Yet, there are conflicting reports in the literature as to whether there is higher PAI activity in patients with myocardial infarction (MI) than in patients with coronary artery disease (CAD) without previous MI. In this retrospective study, t-PA activity, t-PA antigen, and PAI activity before and after a venous occlusion test (VOT) of 10 min were assessed in 109 patients with angiographically documented CAD, in two subgroups of CAD patients with (n = 66) or without (n = 43) previous MI, and in subgroups of CAD patients according to their triglyceride levels and other risk factors. The mean values of t-PA activity in the whole patient group showed a 100-fold increase and a 3.1-fold increase in t-PA antigen after VOT (0.03 +/- 0.03 to 3.0 +/- 6.8 U/ml and 16.5 +/- 6.9 to 51.0 +/- 25.4 ng/ml, p < 0.05). PAI activity was 24.4 +/- 11.0 before and 19.6 +/- 13.2 U/ml after VOT. Within the CAD group, no difference was found between patients without MI and survivors of previous MI in PAI activity before VOT (24.6 +/- 10.7 vs. 24.3 +/- 11.3 U/ml) and after VOT (19.0 +/- 12.1 vs 20.0 +/- 14.0 U/ml), or t-PA activity before (0.03 +/- 0.01 vs. 0.04 +/- 0.04 U/ml) and after VOT (2.8 +/- 7.0 vs. 3.2 +/- 6.7 U/ml). In 39.4% of CAD patients elevated plasma PAI activity before VOT (> 25 U/ml) was found. This subgroup of patients represented the highest PAI activity after VOT (p < 0.05), the lowest t-PA activity after VOT (p < 0.001), and the highest triglyceride levels (p < 0.05). In 11% of the patients, a small increase in t-PA activity (less than 0.5 U/ml) after VOT was seen. This group showed the lowest t-PA antigen after VOT (p < 0.001) and the highest fibrinogen level (p < 0.05). Both subgroups showed the same distribution among patients with and without MI. CAD patients with triglyceride levels over 200 mg/dl had the highest PAI activity values before VOT (28.3 +/- 11.8 U/ml; p < 0.01) and after VOT (24.9 +/- 13.2 U/ml; p < 0.01), resulting in low t-PA activity after VOT (p < 0.01).(ABSTRACT TRUNCATED AT 400 WORDS)

Studies of reperfusion injury in skeletal muscle: controlled limb reperfusion to reduce post-ischaemic syndrome

Revascularization after prolonged complete limb ischaemia may result in both severe damage to skeletal muscle and various systemic manifestations of the postischaemic syndrome. Previous experimental studies performed by the authors have shown that these are caused, to a large extent, by normal reperfusion at normal systemic pressure and that this additional injury can be substantially reduced by controlled reperfusion of the revascularized limb before restoration of the normal circulation. This treatment includes control of the conditions of reperfusion and composition of the initial reperfusate. In the present study, this concept of controlled limb reperfusion was applied to patients with prolonged severe lower limb ischaemia. Controlled limb reperfusion was used in 11 patients after prolonged complete unilateral or bilateral ischaemia. The ischaemic interval ranged from 5 to 21 h. Two patients were in cardiogenic shock, ten had a history of associated cardiac disease and seven coexistent peripheral vascular disease. After systemic heparinization, thromboembolectomy was undertaken using a Fogarty catheter. Cannulas were placed in the iliac, profunda and superficial femoral arteries and connected to a reperfusion set. Oxygenated blood was drawn from the iliac artery and mixed with an asanguineous solution (ratio 6:1). This controlled reperfusate was returned to the profunda and superficial femoral arteries using a single roller pump. The system allows control of both the composition of the reperfusate (Ca2+, pH, osmolarity, glucose, substrate, PO2, free radical scavengers) and the conditions of reperfusion (pressure, flow, temperature). After 30 min of controlled limb reperfusion, the cannulas were removed, the arteriotomy closed and normal blood reperfusion started.(ABSTRACT TRUNCATED AT 250 WORDS)

Changing patterns of patients undergoing emergency surgical revascularization for acute coronary occlusion. Importance of myocardial protection techniques

Between 1977 and 1992 a total of 163 consecutive patients underwent emergency coronary artery bypass grafting after acute coronary occlusion (94% after failed angioplasty). Patients were divided into four groups according to the method used for myocardial protection. The crystalloid cardioplegia group included 30 patients operated on from 1977 to 1980; the hypothermic fibrillation group included 60 patients (1980 to 1986); the blood cardioplegia group included 36 patients (1986 to 1989); and the blood cardioplegia with controlled reperfusion group included 37 patients (1989 to 1992). Preoperative data, ischemic time interval, collateral blood flow, intraoperative data, regional wall motion, global ejection fraction, myocardial infarct-specific electrocardiographic changes, enzyme release, rhythm disturbances, mortality, prevalence of intraaortic balloon pumping, and inotropic support were assessed in this retrospective study. Our data indicate that the current spectrum of patients undergoing emergency coronary artery bypass grafting after acute coronary occlusion are at a significantly higher risk compared with those 15 years ago, that is, increase in age (53 +/- 1 versus 59 +/- 2 years; p < 0.05), three-vessel disease (38% versus 3%; p = 0.004), acute occlusion of the left main coronary artery (11% versus 0%; p = 0.02), preoperative cardiogenic shock (35% versus 3%; p = 0.007), prevalence of acute two-vessel occlusion (22% versus 3%; p = 0.05), prevalence of previous infarction (59% versus 23%; p = 0.04), and duration of ischemia (3.0 +/- 0.2 versus 4.1 +/- 0.3 hours; p < 0.05). Despite the increase in patients with severely compromised ventricular function during recent years, the overall hospital mortality decreased to 5% (2/37) when maximal protection of the ischemic and remote myocardium was performed (preoperative intraaortic balloon pump, combined antegrade/retrograde substrate-enriched blood cardioplegia, warm induction, controlled reperfusion, prolonged vented bypass). Single-vessel disease was always associated with a low mortality, whereas mortality could be reduced with controlled blood cardioplegia in patients with multivessel disease (6%) and cardiogenic shock (15%). The immediate return of regional contractility in the previously ischemic area after controlled reperfusion might serve as an explanation for these favorable results. After unmodified blood reperfusion, normokinesis or slight hypokinesis occurs in only 34% to 46% in the early postoperative period (1 to 4 weeks) in comparison with 86% after controlled blood cardioplegia reperfusion (p < 0.05). We conclude that there is a significant increase in risk factors in patients undergoing emergency coronary artery bypass grafting and that improved methods of intraoperative myocardial protection are needed for these compromised patients.

Left main coronary artery stenosis after aortic valve replacement: genetic disposition for accelerated arteriosclerosis after injury of the intact human coronary artery?

BACKGROUND

Left main coronary artery stenosis is a rare but life-threatening complication after aortic valve replacement because of coronary perfusion-related trauma to the vessel wall with cannulation of the coronary ostia. We investigated whether this complication still occurs in the 1990s despite the use of more advanced catheter materials and modern surgical preservation techniques.

METHODS

Four years after identification of the first two cases in 1987, five further patients had developed left main coronary artery stenosis after aortic valve replacement (incidence, 0.9%) at the cardiothoracic clinic of the J.W. Goethe University and were studied for contributing factors.

RESULTS

Severe coronary ostial stenosis developed within 1 to 6 months after aortic valve replacement. In one such case, intimal proliferation was seen in a biopsy specimen that was comparable to the restenosis induced by coronary angioplasty. The clinical characteristics of the patients developing the complication, the surgical technique, and the intraoperative course did not differ from the other patients. However, five of the seven patients (71%) had a common genetic trait concerning their apolipoprotein E genotype (the epsilon 4 allele) that is normally present in only 10% to 15% of patients screened (P < 0.01).

CONCLUSIONS

These lesions seem to result from a uniform response of the vessel wall to injury. Their incidence is probably related in part to the degree of injury after trauma to the coronary ostia during cannulation for myocardial protection. Patients with the epsilon 4 allele might be genetically predisposed for a pathologically increased response of proliferative repair mechanisms after arterial injury. The complication can be avoided by not instrumenting the coronary ostia for direct antegrade cardioplegia but using retrograde delivery as an alternative method of myocardial protection.

Cardiopulmonary dysfunction produced by reoxygenation of immature hypoxemic animals supported by cardiopulmonary bypass. Prevention by intravenous metabolic pretreatment

This study tests the hypothesis that reoxygenation injury is produced when cardiopulmonary bypass is initiated in immature hypoxemic piglets and that it causes cardiopulmonary dysfunction that can be avoided by intravenous metabolic treatment before and during cardiopulmonary bypass. Of 18 immature Yorkshire-Duroc piglets (aged < 3 weeks), six were anesthetized, instrumented, and observed for 5 hours (control animals). Twelve piglets underwent up to 2 hours of hypoxemia (arterial oxygen tension = 20 to 30 mm Hg) before initiation of reoxygenation on cardiopulmonary bypass. Six received an intravenous metabolic infusion solution (mercaptopropionyl glycine, catalase, aspartate, glutamate, glucose/insulin), which was started before and continued during cardiopulmonary bypass. Hypoxia produced an initial hyperdynamic response (39% increase in cardiac index; p < 0.05) followed by progressive hemodynamic deterioration, necessitating premature initiation of bypass in 8 of 12 hypoxemic piglets (67%). Reoxygenation-induced injury (assessed 30 minutes after cardiopulmonary bypass) was characterized by 39% reduction of stroke work index (p < 0.05), increased myocardial lipid peroxidation (79% increase of conjugated dienes; p < 0.05), 254% increase in pulmonary vascular resistance index (p < 0.05), 22% decrease in static lung compliance (p < 0.05), and 50% decrease in arterial/alveolar oxygen tension ratio (p < 0.05). These reoxygenation changes were avoided by intravenous metabolic treatment. We conclude that the reoxygenation of immature hypoxemic piglets by initiating cardiopulmonary bypass results in cardiopulmonary dysfunction that may increase vulnerability to subsequent ischemia (i.e., aortic crossclamping). The cardiopulmonary reoxygenation changes are preventable by intravenous metabolic treatment before and during cardiopulmonary bypass needed for cardiac repair.

[Decreased fibrinolytic capacity in coronary patients by increased plasminogen activator inhibitor activity]

The fibrinolytic capacity of the blood mainly depends on the amount of tissue-plasminogen activator (t-PA) antigen and plasminogen activator inhibitor (PAI). In this study the fibrinolytic response to a venous occlusion test (VOT) was measured in 109 patients with angiographically documented coronary artery disease (CAD) and in 20 healthy volunteers at comparable age (controls). CAD-patients had higher plasma plasminogen activator inhibitor capacity before (24.4 +/- 11.0 vs. 15.4 +/- 5.2 arbitrary units [AU/ml]; p less than 0.0002) and after VOT (19.6 +/- 13.2 vs. 10.9 +/- 5.3 AU/ml; p less than 0.0001) compared with controls. Furthermore they showed significant lower plasma t-PA activity after VOT (3.0 +/- 6.8 vs. 6.6 +/- 10.6 AU/ml; p less than 0.0001). However there were no difference between both groups in plasma t-PA antigen levels after VOT (17.3 +/- 12.1 vs. 18.7 +/- 14.4 ng/ml). In 10% of patients the decrease in fibrinolytic activity resulted from a lower t-PA release ("lower" was defined as mean minus one standard deviation of the control group). 40% showed elevated plasma PAI capacity before VOT ("elevated" was defined as mean plus two standard deviations of the control group). Both caused significantly reduced post occlusion plasma t-PA activity and prolonged Euglobulin clot lysis time (p less than 0.003). A positive correlation was found between PAI capacity and serum triglyceride levels. Reduced fibrinolytic activity in 109 patients with coronary heart disease based either on a decrease in t-PA antigen release or a increased in PAI capacity in comparison with healthy controls. The mechanism of these findings is not yet well-known.(ABSTRACT TRUNCATED AT 250 WORDS)