Peripheral vascular resistance and angiotensin II levels during pulsatile and non-pulsatile cardiopulmonary bypass

The Conundrum of Systemic Arterial Pressure Management on Cardiopulmonary Bypass

The recently released EACTS/EACTA/EBCP guidelines on cardiopulmonary bypass (CPB) in adult cardiac surgery [...].

Efficacy of Pulsatile Flow Perfusion in Adult Cardiac Surgery: Hemodynamic Energy and Vascular Reactivity

Background: The role of pulsatile (PP) versus non-pulsatile (NP) flow during a cardiopulmonary bypass (CPB) is still debated. This study’s aim was to analyze hemodynamic effects, endothelial reactivity and erythrocytes response during a CPB with PP or NP. Methods: Fifty-two patients undergoing an aortic valve replacement were prospectively randomized for surgery with either PP or NP flow. Pulsatility was evaluated in terms of energy equivalent pressure (EEP) and surplus hemodynamic energy (SHE). Systemic (SVRi) and pulmonary (PVRi) vascular resistances, endothelial markers levels and erythrocyte nitric-oxide synthase (eNOS) activity were collected at different perioperative time-points. Results: In the PP group, the resultant EEP was 7.3% higher than the mean arterial pressure (MAP), which corresponded to 5150 ± 2291 ergs/cm³ of SHE. In the NP group, the EEP and MAP were equal; no SHE was produced. The PP group showed lower SVRi during clamp-time (p = 0.06) and lower PVRi after protamine administration and during first postoperative hours (p = 0.02). Lower SVRi required a higher dosage of norepinephrine in the PP group (p = 0.02). Erythrocyte eNOS activity results were higher in the PP patients (p = 0.04). Renal function was better preserved in the PP group (p = 0.001), whereas other perioperative variables were comparable between the groups. Conclusions: A PP flow during a CPB results in significantly lower SVRi, PVRi and increased eNOS production. The clinical impact of increased perioperative vasopressor requirements in the PP group deserves further evaluation.

Kidney Microcirculation as a Target for Innovative Therapies in AKI

Acute kidney injury (AKI) is a serious multifactorial conditions accompanied by the loss of function and damage. The renal microcirculation plays a crucial role in maintaining the kidney’s functional and structural integrity for oxygen and nutrient supply and waste product removal. However, alterations in microcirculation and oxygenation due to renal perfusion defects, hypoxia, renal tubular, and endothelial damage can result in AKI and the loss of renal function regardless of systemic hemodynamic changes. The unique structural organization of the renal microvasculature and the presence of autoregulation make it difficult to understand the mechanisms and the occurrence of AKI following disorders such as septic, hemorrhagic, or cardiogenic shock; ischemia/reperfusion; chronic heart failure; cardiorenal syndrome; and hemodilution. In this review, we describe the organization of microcirculation, autoregulation, and pathophysiological alterations leading to AKI. We then suggest innovative therapies focused on the protection of the renal microcirculation and oxygenation to prevent AKI.

Pulmonary Congestion Due to Right and Left Heart Output Mismatching: A Case Report and Literature Review

We report a new pulmonary circulation model during cardiopulmonary bypass that is able to cause pulmonary congestion but without left heart failure. This kind of congestion is characterized by right and left heart output mismatching. The pathophysiological mechanism, clinical manifestations, diagnosis, differential diagnosis, and treatment of this pulmonary congestion are reviewed and discussed in the following article.

The Use of Angiotensin II for the Treatment of Post-cardiopulmonary Bypass Vasoplegia

Purpose

Vasoplegia is a common complication after cardiac surgery and is related to the use of cardiopulmonary bypass (CPB). Despite its association with increased morbidity and mortality, no consensus exists in terms of its treatment. In December 2017, angiotensin II (AII) was approved by the Food and Drug Administration (FDA) for use in vasodilatory shock; however, except for the ATHOS-3 trial, its use in vasoplegic patients that underwent cardiac surgery on CPB has mainly been reported in case reports. Thus, the aim of this review is to collect all the clinically relevant data and describe the pharmacologic mechanism, efficacy, and safety of this novel pharmacologic agent for the treatment of refractory vasoplegia in this population.

Methods

Two independent reviewers performed a systematic search in PubMed, Embase, Web of Science, and Cochrane Library using relevant MeSH terms (Angiotensin II, Vasoplegia, Cardiopulmonary Bypass, Cardiac Surgical Procedures).

Results

The literature search yielded 820 unique articles. In total, 9 studies were included. Of those, 2 were randomized clinical trials (RCTs) and 6 were case reports and 1 was a retrospective cohort study.

Conclusions

AII appears to be a promising means of treatment for patients with post-operative vasoplegia. It is demonstrated to be effective in raising blood pressure, while no major adverse events have been reported. It remains uncertain whether this agent will be broadly available and whether it will be more advantageous in the clinical management of vasoplegia compared to other available vasopressors. For that reason, we should contain our eagerness and enthusiasm regarding its use until supplementary knowledge becomes available.

Electronic supplementary material

The online version of this article (10.1007/s10557-020-07098-3) contains supplementary material, which is available to authorized users.

Effects of milrinone on renal perfusion, filtration and oxygenation in patients with acute heart failure and low cardiac output early after cardiac surgery

PURPOSE

Early postoperative heart failure is common after cardiac surgery, and inotrope treatment may impact renal perfusion and oxygenation. We aimed to study the renal effects of the inodilator milrinone when used for the treatment of heart failure after weaning from cardiopulmonary bypass (CPB).

MATERIAL AND METHODS

In 26 patients undergoing cardiac surgery with CPB, we used renal vein catheterization to prospectively measure renal blood flow (RBF), glomerular filtration rate (GFR), and renal oxygenation. Patients who developed acute heart failure and low cardiac output (cardiac index <2.1 L/min/m²) at 30 min after weaning from CPB (n = 7) were given milrinone, and the remaining patients (n = 19) served as controls. Additional measurements were made at 60 min after CPB.

RESULTS

In patients with acute postoperative heart failure, before receiving milrinone, renal blood flow was lower (-33%, p < .05) while renal oxygen extraction was higher (41%, p < .05) compared to the control group. Milrinone increased cardiac index (21%, p < .001), RBF (36%, p < .01) and renal oxygen delivery (35%, p < .01), with no significant change in GFR and oxygen consumption compared to the control group.

CONCLUSIONS

In patients with acute heart failure after weaning from CPB, the milrinone-induced increase in cardiac output was accompanied by improved renal oxygenation.

TRIAL REGISTRATION

ClinicalTrials.gov; identifier NCT02405195, date of registration; March 27, 2015, and NCT02549066, date of registration; 9 September 2015.

The outcome of pediatric patients undergoing congenital cardiac surgery under pulsatile cardiopulmonary bypass in different frequencies

Purpose

To investigate the influence and possible pathophysiological mechanism of pulsatile cardiopulmonary bypass (CPB) in various frequencies in pediatric patients undergoing congenital cardiac surgery.

Patients and methods

Clinical data and hemodynamic parameters were collected in 80 patients who underwent congenital cardiac surgeries and were perfused in different settings: pulsatile perfusion (PP) in frequencies of 30 beats/min, PP 60 beats/min, PP 100 beats/min and non-pulsatile perfusion (NP). Serum proteins, plasma-free hemoglobin (PFH), endothelin-1 (ET-1) and nitric oxide (NO) were collected to study possible pathophysiological changes, possible hematological injury and oxidative status under different perfusing conditions.

Results

Patients in all groups had similar baseline characteristics, aortic cross-clamping time and CPB duration. More effective pulse gradient (PG), energy-equivalent pressure (EEP) and surplus hemodynamic energy (SHE) were observed in pulsatility with lower frequency setting, under which more patients achieved physiologically normal mean arterial pressure (MAP), without the support of inotropic agents during bypass. Significant between-group differences of serum proteins and PFH were absent the whole time during and after bypass, while a relatively lower percentage of perioperative requirement of diuretics was observed in the low frequency pulsatile group. A better performance to oxidative stress was seen in the low frequency group with higher levels of NO and lower concentration of ET-1, and both intergroup differences were found (P<0.01). Satisfactory clinical outcome was obtained on post procedure course in all groups.

Conclusion

Pulsatile perfusion with low frequency setting in pediatric patients undergoing congenital cardiac surgery showed better hemodynamic profiles, potential protective effects on vital organs, better oxidative status and satisfactory clinical outcome.

Vasoactive Pressure Hormones during and after Cardiopulmonary Bypass

The differences in the pattern of the vasoactive hormone release in response to the stress of surgery and cardiopulmonary bypass (CPB) (pulsatile n = 15 and non pulsatile n = 23) were studied in the adult patients with mitral valve disease (MVD), aortic valve disease (AVD), and the coronary artery disease (CAD). A differential stimulation of the osmoreceptors, baroceptors, renin-angiotensin and the sympathetico-adrenal systems in these patients, resulted in the variations in the pattern of hormone release. Patients with MVD showed a greater stimulation of osmoreceptors, baroceptors and release of Arginine vasopressin (AVP). Renin-angiotensin system was more easily triggered in patients with AVD or CAD; and sympathetico-adrenal system in patients with CAD. The renin-angiotensin-aldosterone axis was better preserved in patients with CAD (r = 0.49, p < 0.001) than in the patients with MVD (r = 0.38, p < 0.02). Plasma renin release showed a significant correlation with noradrenaline release in the patients with MVD (r = 0.47, p < 0.01); but this relationship was lost in the patients with the CAD, due to an excessive noradrenaline release. Pulsatile bypass reduced but did not abolish this response. Under unfavourable conditions, the stress response may persist in the early post-operative period.

Mechanical ventricular support using pulsatile Abiomed BVS 5000 and centrifugal Biomedicus-pump in postcardiotomy shock

Since we started using ventricular assist devices (VAD) in July 1987 up to August 1993, 63 of 15,650 (0.4%) patients (pts) who underwent open heart sugery were supported postoperatively by VAD at out institution. Forty-three were male and 20 female, mean age 55.5 years. In 49 pts coronary artery bypass grafting (CABG), in 8 pts valve surgery, in 3 pts combined CABG and valve surgery and in 3 pts corrective procedures for congenital heart disease were performed. Perioperative myocardial infarction was the most frequent indication (73%). In 37 of the 63 pts (58.7%) a centrifugal (Biomedicus pump (group A) was used and in 26 pts (41.3%) a pulsatile Abiomed BVS 5000 (group B). Fourteen of 37 pts (38%) in group A were weaned from the VAD and all of them were discharged. Twenty-three pts were unable to be weaned and 19 of these pts died. The remaining 4 pts were transplanted successfully and subsequently 3 died and 1 was discharged. In all, 15 pts (39%) were long-term survivors. Sixteen of 26 pts (62%) in group B were weaned from VAD and 13 (50%) of them were discharged of whom 3 died. Ten patients were unable to be weaned and 7 of these died. The remaining 3 pts were transplanted successfully. In all, 16 pts (61.5%) were long-term survivors. The shorter the interval between beginning resuscitation and application of VAD the better the outcome. Younger age, VAD installation in OR, support time between 2 and 7 days and Abiomed pump, influence the survival rate positively. Because of higher recovery and survival rates in patients assisted by Abiomed compared to the Biomedicus pump, we recommend the Abiomed pump in postcardiotomy cardiac failure.

GNAQ TT(-695/-694)GC Polymorphism Is Associated with Increased Gq Expression, Vascular Reactivity, and Myocardial Injury after Coronary Artery Bypass Surgery

BACKGROUND

Angiotensin II receptor type 1-mediated activation of the α-subunit of the heterotrimeric Gq protein evokes increased vasoconstriction and may promote hypertrophy-induced myocardial damage. The authors recently identified a TT(-695/-694)GC polymorphism in the human Gq promoter, the GC allele being associated with an increased prevalence of cardiac hypertrophy. In this article, the authors tested whether the TT(-695/-694)GC polymorphism is associated with differences in (1) myocardial Gq protein expression, (2) vascular reactivity, and (3) myocardial damage after coronary artery bypass grafting.

METHODS

Gq protein expression was measured in right atrial muscle from 55 patients undergoing coronary artery bypass grafting as were skin perfusion changes (n = 18; laser Doppler imaging), saphenous vein ring vascular reactivity (n = 50, organ bath) in response to angiotensin II, and myocardial damage (227 patients undergoing coronary artery bypass grafting), as assessed by postoperative cardiac troponin I concentration.

RESULTS

Myocardial Gq expression was greater in GC/GC genotypes (GC/GC vs.

TT/TT

1.27-fold change; P = 0.006). Skin perfusion after intradermal angiotensin II injection decreased only in GC/GC genotypes (P = 0.0002). Saphenous vein rings exposed to increasing angiotensin II concentrations showed an almost doubled maximum contraction in GC/GC compared with individuals with the TT/TT genotype (P = 0.022). In patients undergoing coronary artery bypass grafting, baseline cardiac ejection fraction was different (GC/GC: 55 ± 13%; GC/TT: 54 ± 14%; TT/TT: 48 ± 15%; P = 0.037) and postoperative peak cardiac troponin I was greater in patients with the GC/GC (11.5 ± 13.8 ng/ml) than in patients with the GC/TT (9.2 ± 9.2 ng/ml) or patients with the TT/TT genotype (6.6 ± 4.8 ng/ml, P = 0.015).

CONCLUSIONS

The GC/GC genotype of the TT(-695/-694)GC polymorphism is associated with increased Gq protein expression, augmented angiotensin II receptor type 1-related vasoconstriction, and increased myocardial injury after coronary artery bypass grafting, highlighting the impact of Gq genotype variation.

Angiotensin Receptor Blockade Improves Cardiac Surgical Outcomes in Patients With Metabolic Syndrome

BACKGROUND

Perioperative use of angiotensin receptor blockers (ARBs) and angiotensin-converting enzyme inhibitors (ACEis) in patients undergoing cardiac operations remains controversial. The current practice of discontinuing renin-angiotensin-system inhibitors preoperatively may negate their beneficial effects in vulnerable populations, including patients with metabolic syndrome, who exhibit elevated renin-angiotensin system activity. We hypothesized that preoperative ARB use is associated with reduced incidence of postoperative complications, compared with ACEi or no drug, in patients with metabolic syndrome undergoing coronary artery bypass grafting.

METHODS

We used propensity matching to derive a cohort of 1,351 patients from 2,998 who underwent coronary artery bypass grafting based on preoperative use of ARBs, ACEis, or no renin-angiotensin-system inhibitors. Our primary end point was a composite of adverse events occurring within 30 days after the operation: new-onset atrial fibrillation/flutter, arrhythmia requiring cardioversion, perioperative myocardial infarction, acute renal failure, need for dialysis, cerebrovascular accidents, acute respiratory failure, or perioperative death.

RESULTS

At least one adverse event occurred in 524 (38.8%) of matched cohort patients (1,184 [39.6% of all patients]). Adjusting for European System for Cardiac Operative Risk Evaluation and metabolic syndrome in the matched cohort, preoperative use of ARBs was associated with a lower incidence of adverse events in patients with metabolic syndrome compared with preoperative use of no renin-angiotensin-system inhibitors (odds ratio, 0.43; 95% confidence interval, 0.19 to 0.99) or ACEis (odds ratio, 0.38; 95% confidence interval, 0.16 to 0.88).

CONCLUSIONS

Preoperative use of ARBs, but not ACEis, confers a benefit within 30 days after cardiac operations in patients with metabolic syndrome, suggesting potential efficacy differences of these drug classes in reducing cardiovascular morbidity and death in ambulatory vs surgical patients.

Pulse pressure-dependent cerebrovascular eNOS regulation in mice

Arterial blood pressure is oscillatory; whether pulse pressure (PP) regulates cerebral artery myogenic tone (MT) and endothelial function is currently unknown. To test the impact of PP on MT and dilation to flow (FMD) or to acetylcholine (Ach), isolated pressurized mouse posterior cerebral arteries were subjected to either static pressure (SP) or a physiological PP (amplitude: 30 mm Hg; frequency: 550 bpm). Under PP, MT was significantly higher than in SP conditions ( p < 0.05) and was not affected by eNOS inhibition. In contrast, under SP, eNOS inhibition increased ( p < 0.05) MT to levels observed under PP, suggesting that PP may inhibit eNOS. At a shear stress of 20 dyn/cm², FMD was lower ( p < 0.05) under SP than PP. Under SP, eNOS-dependent [Formula: see text] production contributed to FMD, while under PP, eNOS-dependent NO was responsible for FMD, indicating that PP favours eNOS coupling. Differences in FMD between pressure conditions were abolished after NOX2 inhibition. In contrast to FMD, Ach-induced dilations were higher ( p < 0.05) under SP than PP. Reactive oxygen species scavenging reduced ( p < 0.05) Ach-dependent dilations under SP, but increased ( p < 0.05) them under PP; hence, under PP, Ach promotes ROS production and limits eNOS-derived NO activity. In conclusion, PP finely regulates eNOS, controlling cerebral artery reactivity.

Effects of Cardiopulmonary Bypass on Renal Perfusion, Filtration, and Oxygenation in Patients Undergoing Cardiac Surgery

Background

Acute kidney injury is a common complication after cardiac surgery with cardiopulmonary bypass. The authors evaluated the effects of normothermic cardiopulmonary bypass on renal blood flow, glomerular filtration rate, renal oxygen consumption, and renal oxygen supply/demand relationship, i.e., renal oxygenation (primary outcome) in patients undergoing cardiac surgery.

Methods

Eighteen patients with a normal preoperative serum creatinine undergoing cardiac surgery procedures with normothermic cardiopulmonary bypass (2.5 l · min−1 · m−2) were included after informed consent. Systemic and renal hemodynamic variables were measured by pulmonary artery and renal vein catheters before, during, and after cardiopulmonary bypass. Arterial and renal vein blood samples were taken for measurements of renal oxygen delivery and consumption. Renal oxygenation was estimated from the renal oxygen extraction. Urinary N-acetyl-β-d-glucosaminidase was measured before, during, and after cardiopulmonary bypass.

Results

Cardiopulmonary bypass induced a renal vasoconstriction and redistribution of blood flow away from the kidneys, which in combination with hemodilution decreased renal oxygen delivery by 20%, while glomerular filtration rate and renal oxygen consumption were unchanged. Thus, renal oxygen extraction increased by 39 to 45%, indicating a renal oxygen supply/demand mismatch during cardiopulmonary bypass. After weaning from cardiopulmonary bypass, renal oxygenation was further impaired due to hemodilution and an increase in renal oxygen consumption, accompanied by a seven-fold increase in the urinary N-acetyl-β-d-glucosaminidase/creatinine ratio.

Conclusions

Cardiopulmonary bypass impairs renal oxygenation due to renal vasoconstriction and hemodilution during and after cardiopulmonary bypass, accompanied by increased release of a tubular injury marker.

Review Article: Comparison of perfusion modes on microcirculation during acute and chronic cardiac support: is there a difference?

Although heart-lung machines and cardiac assist devices have been used successfully for acute and chronic cardiac support for decades, controversies still remain concerning the benefits of pulsatile and non-pulsatile perfusion. The core of the debate is whether enough energy is generated by the artificial pulse to keep capillary beds open and cell metabolism stabilized during acute or chronic cardiac support. In other words, does artificial pulsatility exist in the microcirculation: small vessels of less than 100 μm in diameter? Many investigators have tried to use different tools and biomarkers to reflect directly or indirectly the state of the microcirculation when comparing the two different perfusion modes during acute and chronic cardiac support. However, the results are controversial. First, direct observation of the state of the microcirculation during acute and chronic cardiac support is limited; and reports concerning direct observation of the microcirculation with different perfusion modes in contemporary literature are rare. Secondly, different investigators have used their own criteria to define pulsatile flow. Therefore, it is necessary to develop more efficient methodologies, enabling direct observation of the microcirculation during acute and chronic cardiac support and also establish common criteria that will precisely quantify the pulsatile flow in terms of energy equivalent pressure (EEP) and surplus hemodynamic energy (SHE) levels. Using these critical parameters may explain how excess energy is created by pulsatile flow and maintains perfusion through the microcirculation by ensuring capillary patency. Perfusion (2007) 22, 115—119.

Plasma levels of glucose, insulin and cortisol in children undergoing cardiac surgery: effects of pulsatile and nonpulsatile perfusion

The effects of pulsatile and nonpulsatile perfusion on the plasma glucose, insulin and cortisol levels were studied in 12 children undergoing intracardiac repair of congenital heart defects. Hyperglycaemia was noted in both subgroups during the operation but plasma glucose returned to normal levels at 24 hours. Insulin secretion was suppressed during the period of extracorporeal circulation (ECC) and this was pronounced while the aorta was crossclamped. Cortisol levels were elevated during the whole period of study and remained elevated at 24 hours. In the pulsatile group cortisol levels were higher than the nonpulsatile group. However there was no significant difference between the groups.

Like adults, children exhibit a metabolic response during open-heart operations. Pulsatile perfusion delivered by a modified Stöckert roller pump during ECC, did not alter the glucose, insulin and cortisol response to cardiac surgery in this study.

The effect of normothermic cardiopulmonary bypass on hepatic blood flow in the dog

Hepatic blood flow was investigated in two groups of eight anaesthetized dogs during and after one hour of either pulsatile or non-pulsatile cardiopulmonary bypass (CPB). Mean perfusion pressure was maintained at 60 mmHg. Hepatic arterial (HA) and portal venous (PV) blood flows were measured using electromagnetic flow probes, and hepatic O 2 consumption determined. The results demonstrate that: (a) pulsatile CPB reduces peripheral vascular resistance during and after perfusion, and more effectively preserves pump flow rate and cardiac output than non-pulsatile CPB; (b) total liver blood flow is sustained more effectively by pulsatile CPB than by non-pulsatile CPB due to relative preservation of both HA and PV flows; (c) hepatic O2 consumption is only marginally better preserved during and after pulsatile CPB than with non-pulsatile perfusion. We conclude that: (a) pulsatile CPB tends to maintain hepatic blood flow through a relative reduction in HA vascular resistance and an improvement in PV flow produced passively by a greater pump flow rate; (b) pulsatile CPB less effectively benefits hepatic O2 consumption because of poor O2 uptake from the hepatic PV blood supply.

Factors affecting the pulsatile hydraulic power output of the Stockert roller pump

A detailed assessment of the hydraulic power output of the Stockert roller pump was performed with the pump operating in its 'pulsatile' mode. Pressure and flow waveforms and the pulsatile power generated in a model of the human vascular bed were dependant upon the pump output, the pump control settings and the diameters of the arterial line, the pump insert and aortic cannula. The pulsatile power output was lower when a silicone rubber pump insert was used rather than a polyvinyl chloride insert. The incorporation of a Cobe CML flat-sheet membrane oxygenator into the arterial line reduced the pulsatile power to levels similar to those obtained with the pump operating in its 'continuous' mode. Incorporating a Sarns hollow fibre membrane oxygenator or a Pall extracorporeal blood filter had less effect and variations in perfusate viscosity or the length of the arterial line did not appear to have any effect. It seems probable that the experimental and clinical effects of 'pulsatile' flow during cardiopulmonary bypass with this pump will be highly dependant upon the operating conditions.

Quantitative analysis of the effect of pulsatile flow on vascular resistance

'Pulsatile flow' has been reported to reduce vascular resistance. In this study, the effect of pulsatile flow was assessed quantitatively, using perfusion of canine hindlimb. The perfusion circuit consisted of roller-type pulsatile pump (Cobe Inc., Stockert pump) and bubble oxygenator (Shiley Inc., S-070/s). Each flow curve was quantified with the mean flow rate (F) and pulse power index (PPI). PPI is derived by Fourier transformation of the flow curve and represents the degree of 'pulsation'. Vascular resistance was determined during perfusion with varied flow rate and PPI. The regression formula between vascular resistance (VR) and two parameters was obtained as follows:

VR(F,PPI) = 41600x(F-1.37) -0.95+913 - PPIx{(3.99x(F-1.33)-040_0.69}

where VR is measured in mmHg. min-1.kg.ml-1; F represents ml.min-1.kg -1 (range from 2.8 to 17.1); and PPI is dimensionless (range from 2.8 to 215.7).

Using this formula, vascular resistance at a fixed flow rate and wave form can be predicted. When the flow rate is 6.27 ml.min-1.kg-1 and the PPI is 1466, (measured values under perfusion with own beating heart) the vascular resistance perfused by own beating heart is obtained. The results indicate that the pulsation of own beating heart contributes to a reduction in vascular resistance to 80%. It is also shown that the value of PPI which is necessary to reduce the vascular resistance to 80% is more than 1300 under the normal flow rate range.

Effects on the Endocrine System of Pulsatile and Nonpulsatile Perfusion in Heart Surgery

The effects of cardiopulmonary bypass on the endocrine system were investigated in 10 patients who had pulsatile perfusion and in another 10 who had nonpulsatile perfusion during coronary bypass or valve replacement surgery. Measurements were made of thyroid-stimulating hormone, free and total triiodothyronine, free and total tetraiodothyronine, adrenocorticotropic hormone, cortisol, aldosterone, growth hormone, insulin, and glucose at 5 fixed time intervals up to 24 hours postoperatively. In the perfusion period, free and total triiodothyronine levels were less depressed in the pulsatile group. The mean level of growth hormone was significantly higher in the pulsatile group after 60 minutes of perfusion. The mean levels of insulin and glucose were significantly lower in the pulsatile group after 60 minutes of perfusion. Other changes were not statistically significant. We concluded that pulsatile perfusion was of benefit in stabilizing glucose and some hormone levels.

Lifelong Cyclic Mechanical Strain Promotes Large Elastic Artery Stiffening: Increased Pulse Pressure and Old Age-Related Organ Failure

The arterial wall is under a huge mechanical constraint imposed by the cardiac cycle that is bound to generate damage with time. Each heartbeat indeed imposes a pulsatile pressure that generates a vascular stretch. Lifetime accumulation of pulsatile stretches will eventually induce fatigue of the elastic large arterial walls, such as aortic and carotid artery walls, promoting their stiffening that will gradually perturb the normal blood flow and local pressure within the organs, and lead to organ failure. The augmented pulse pressure induced by arterial stiffening favours left ventricular hypertrophy because of the repeated extra work against stiff high-pressure arteries, and tissue damage as a result of excessive pulsatile pressure transmitted into the microcirculation, especially in low resistance/high-flow organs such as the brain and kidneys. Vascular aging is therefore characterized by the stiffening of large elastic arteries leading to a gradual increase in pulse pressure with age. In this review we focus on the effect of age-related stiffening of large elastic arteries. We report the clinical evidence linking arterial stiffness and organ failure and discuss the molecular pathways that are activated by the increase of mechanical stress in the wall. We also discuss the possible interventions that could limit arterial stiffening with age, such as regular aerobic exercise training, and some pharmacological approaches.

Pulsatile flow decreases gaseous micro-bubble filtering properties of oxygenators without integrated arterial filters during cardiopulmonary bypass

OBJECTIVES

Cardiopulmonary bypass (CPB) has a risk of embolic injury with an important role of gaseous micro-bubbles (GMBs), coming from CPB-circuit. Pulsatile perfusion (PP) can provide specific conditions for supplementary GMB-activity with respect to non-pulsatile (NP). We aimed to test GMB-filtering properties of three modern oxygenators under pulsatile and non-pulsatile conditions.

METHODS

Seventy-eight patients undergoing on-pump myocardial revascularization were randomized prospectively into three equal groups according to the oxygenator model used during CPB. Terumo Capiox-FX25, Sorin Synthesis or Maquet Quadrox-i-Adult membrane oxygenators were tested. Each group was divided equally to undergo PP or NP. GMBs were counted by means of a GAMPT-BCC200 bubble-counter with two probes placed at preoxygenator and arterial post-filter positions. Results were evaluated in terms of GMB-volume, GMB-number, amount of large over-ranged GMBs, a series of filtering indices and major neurological outcomes.

RESULTS

PP decreased GMB-filtering properties of the tested oxygenators. Those with integrated filters (CAPIOX-FX25 and SYNTHESIS) did not show significant differences between perfusion groups, while QUADROX-i oxygenator with external arterial filter showed significantly higher GMB-volume (P < 0.001), GMB-number (P < 0.001) and amount of over-ranged bubbles (P < 0.001) detected in arterial line during PP. Despite the differences in filtering capacity of all circuits with both types of perfusion, no important differences in clinical outcomes and major neurological events were observed.

CONCLUSIONS

Pulsatile flow decreases gaseous micro-bubble filtering properties of oxygenators without integrated arterial filters during CPB. PP requires specially designed circuit components to avoid the risk of additional GMB delivery.

[Vasoreactivity changes during extracorporeal circulation: effects of halogenated agents]

During cardiopulmonary bypass (CPB), endothelium is exposed to multiple disturbances leading to significant vasomotor tone and vascular systemic resistances (VSR) level modifications. Properties of endothelial function on vascular tone were summarized herein. According bibliographic findings, physiological and clinical impacts of respectively halogenated agents and CPB concerning vasomotor tone were reported. Main effects of halogenated agents administered through oxygenator during CPB were also identified. Usually when administered above one MAC, halogenated agents decreased VSR during hypothermic bypass. Once those mechanisms summarized, increase of halogenated agent's effects on VSR during normothermic CPB was postulated. Assuming that decrease of VSR could be deleterious favoring severe vasoplegia event, clinical experience of administration of isoflurane during CPB among more 4000 patients was retrospectively reported. Incidence of severe vasoplegia was established to 9.5 % in the studied population and this result was similar as others. More over predicting factors of severe vasoplegia were the same as previously reported : severity of preoperative clinical status according Euroscore, hemodynamical instability before induction of anesthesia, surgical procedure complexity and CPB duration. Absence of deleterious effects in SVR decrease when administering isoflurane during normothermic CPB was assumed but prospective comparative studies comparing effects of halogenated agents and other anesthetic agents are needed in order to confirm these findings.

The effect of hemodilution during normothermic cardiac surgery on renal physiology and function: a review

Although the definitions of renal dysfunction vary, loss of renal function is a common complication following cardiac surgery using cardiopulmonary bypass (CPB). When postoperative dialysis is required, mortality is approximately 50%. CPB-accompanied hemodilution is a major contributing factor to renal damage as it notably reduces oxygen delivery by reducing the oxygen transport capacity of the blood as well as disturbing the microcirculation. To minimize hypoxemic damage during CPB, lowering of body temperature is applied to reduce the patient’s metabolic rate. At present, however, temperature management during elective adult cardiac surgery is shifting from moderate hypothermia to normothermia. To determine whether the currently accepted levels of hemodilution during CPB can suffice the normothermic patient’s high oxygen demand, we focused this study on renal physiology and postoperative renal function. Hemodilution reduces the capillary density through a diminished capillary viscosity, thereby, redistributing blood from the renal medulla to the renal cortex. As the physiology of the renal medulla makes it a hypoxic environment, this part of the kidney appears to be especially at risk for hypoxic damage caused by a hemodilution-induced lowered oxygen transport and oxygen delivery. In addition, hemodilution is also likely to disturb the hormonal systems regulating renal blood distribution. Clinical studies, mostly of retrospective or observational nature, show that perioperative nadir hematocrit levels lower than approximately 24% are associated with an increased risk to develop postoperative renal failure. A better comprehension of the cause-and-effect relation between low perioperative hematocrits and loss of postoperative renal function may enable more effective renal protective strategies.

Preoperative methylene blue administration in patients at high risk for vasoplegic syndrome during cardiac surgery

BACKGROUND

Angiotensin-converting enzyme inhibitors, calcium channel blockers, and preoperative intravenous heparin use are independent risk factors for vasoplegic syndrome after cardiac surgery. We prospectively studied whether preoperative methylene blue administration would prevent the vasoplegic syndrome in these high-risk patients.

METHODS

One hundred patients scheduled for coronary artery bypass graft surgery who were at high risk for vasoplegia because they were preoperatively using angiotensin-converting enzyme inhibitors, calcium channel blockers, and heparin were randomly assigned to either receive preoperative methylene blue (group 1, n = 50) or not receive it (group 2, controls, n = 50). Methylene blue (1% solution) was administered intravenously at a dose of 2 mg/kg for more than 30 minutes, beginning in the intensive care unit 1 hour before surgery.

RESULTS

Although similar in terms of all demographic and operative variables, the two groups differed significantly in terms of vasoplegic syndrome incidence (0% in group 1[0 of 50] vs 26% in group 2 [13 of 50]; p < 0.001). In 6 patients, the vasoplegic syndrome was refractory to norepinephrine. Four of these patients survived; the other 2 had vasoplegic syndromes that were refractory to aggressive vasopressor therapy, and they ultimately died of multiorgan failure. Stroke occurred in 1 patient. The two study groups also differed significantly in terms of average intensive care unit stay (1.2 +/- 0.5 days in group 1 vs 2.1 +/- 1.2 days in group 2; p < 0.001) and average hospital stay (6.1 +/- 1.7 days in group 1 vs 8.4 +/- 2.0 days in group 2; p < 0.001).

CONCLUSIONS

Our results suggest that preoperative methylene blue administration reduces the incidence and severity of vasoplegic syndrome in high-risk patients, thus ensuring adequate systemic vascular resistance in both operative and postoperative periods and shortening both intensive care unit and hospital stays.

Effects of left ventricular assist device support and outflow graft location upon aortic blood flow

Although continuous flow (CFVAD) and pulsatile (PVAD) ventricular assist devices (VADs) are being clinically used, their effects upon aortic blood flow as a measure of overall blood distribution remain unclear. The objective of this study was to compare the effects of CFVAD and PVAD support for ascending (AscA) and descending (DA) aorta outflow cannulation upon mean aortic blood flow and waveform morphology. Six experiments were conducted in a normal, acute calf model, in which an inflow cannula was implanted in the left ventricle apex and outflow cannulae were anastomosed to both the AscA and DA. Flow probes were placed around the pulmonary artery, pump outflow, brachiocephalic trunk, and aorta proximal and distal to the DA outflow. For each acute experiment, calves received randomly selected levels of VAD support (0-100% of cardiac output) and pump failure (VAD off and outflow cannula unclamped) for each of four randomly selected test conditions: (1) PVAD and AscA, (2) PVAD and DA, (3) CFVAD and AscA, and (4) CFVAD and DA. Regardless of pump type or support level, proximal and distal aorta mean flows were lower (p < 0.05) for DA compared with the AscA. No differences in mean aortic flows between pump types at either outflow graft location were discerned. Differences in morphologic features of blood flow waveforms between PVAD and CFVAD were observed. During simulated pump failure, retrograde aortic blood flow in both the aortic arch and DA was observed. Partial ventricular suction was also observed during the greatest levels of CFVAD support and suggested pronounced effects upon both the right and left ventricle. Collectively, these findings imply that VAD outflow location may have an important role in patient response and recovery. Investigation of the long-term pathophysiologic responses to pump type and outflow location is ongoing.

A prospective randomized study to evaluate stress response during beating-heart and conventional coronary revascularization

BACKGROUND

Cardiopulmonary bypass (CPB) is associated with a systemic stress hormonal response, which can lead to changes in hemodynamics and organ perfusion. We examined perioperative stress hormone release in low-risk patients undergoing coronary artery bypass grafting with and without cardiopulmonary bypass.

METHODS

Fifty-two patients undergoing primary coronary artery bypass grafting by the same surgeon were randomly assigned into either on-pump (n = 26) or off-pump (n = 26) groups. The on-pump coronary artery bypass grafting group underwent mildly hypothermic (35 degrees C) pulsatile cardiopulmonary bypass with arterial line filtration. Arterial blood samples were collected preoperatively, at the end of operation, and at 1, 6, and 24 hours postoperatively. Plasma levels of vasopressin and cortisol were measured using radioimmunoassay. Anesthetic management was standardized.

RESULTS

Both groups had similar demographic makeup and extent of revascularization (on-pump coronary artery bypass grafting, 2.8 +/- 1.0 grafts versus off-pump coronary artery bypass grafting, 2.4 +/- 0.9 grafts; p = 0.20). No mortality or major morbidity was observed and there were no crossovers. The cardiopulmonary bypass and aortic cross-clamp times in the on-pump coronary artery bypass grafting group were 63 +/- 24 and 33 +/- 11 minutes, respectively. In both groups there was a similar and significant rise in cortisol and vasopressin levels in the early postoperative phase, with a partial recovery toward baseline values observed at 24 hours postoperatively. Repeated measures analysis of covariance showed no significant difference between the groups with time for both hormones (cortisol, p = 0.40; vasopressin, p = 0.30).

CONCLUSIONS

Despite the avoidance of cardiopulmonary bypass, off-pump coronary artery bypass grafting surgery triggers a systemic stress hormone response that is comparable to conventional surgical revascularization. The neurohormonal environment during beating-heart surgery should be further explored.

Microcirculation of the Bulbar Conjunctiva in the Goat Implanted with a Total Artificial Heart: Effects of Pulsatile and Nonpulsatile Flow

A new system to observe the microcirculation on the bulbar conjunctiva was developed using a digital high definition microscope to investigate the influence of the flow patterns on the microcirculation in a goat with a total artificial heart (TAH). The undulation pump TAH was implanted into the goat. When the whole body condition became stable, the flow pattern was modulated between the pulsatile and the nonpulsatile mode, and the changes in the microcirculation were observed. When the flow pattern was changed from pulsatile to nonpulsatile mode, the erythrocyte velocity in capillaries dropped from 526+/-83 to 132+/-41 microm/s and remained at a low level. The number of perfused capillaries decreased as well. Then the nonpulsatile flow mode was maintained for 20 minutes. After the flow pattern was returned to the pulsatile mode again, the erythrocyte velocity recovered to the initial level (433+/-71 microm/s). In many cases, the flow of the nonperfused capillaries in the nonpulsatile mode recovered to the initial level after the flow pattern was changed to the pulsatile mode again. The perfused capillary density in the nonpulsatile mode (19.7+/-4.1 number of capillaries/mm) was significantly lower than that in the pulsatile mode (34.7+/-6.3 number of capillaries/mm). It is thought that the basal and flow stimulated endothelium derived nitric oxide release in the microvessels decreased because of the disappearance of pulsatility and that the nitric oxide induced the constriction of arterioles after the flow pattern was changed to the nonpulsatile mode. At the same time, the baroceptors might sense the decrease in the arterial peak pressure or dp/dt, and the sympathetic nerve increases activities and induce the constriction of arterioles. Then, the erythrocyte velocity in capillaries would decrease. Because of the flow pattern further in the chronic phase, it is important to follow the change in the microcirculation.

[Abdominal complications associated with cardiac surgery. Review of a contemporary surgical experience and of a series done without extracorporeal circulation]

INTRODUCTION

To evaluate the prevalence, risk factors and morbidity associated with gastrointestinal (GI) complications after cardiac surgery, with and without cardiopulmonary bypass, we carried out a retrospective cohort study at a university teaching hospital.

METHODS

We divided the 11,405 eligible adult patients into 2 groups: group A (operated on between January 1992 and June 1996) (4657 patients) and group B (operated on between July 1996 and December 2000) (6748 patients).

RESULTS

We found 147 GI complications in 134 (1.2%) patients. The incidence of GI morbidity was similar for the 2 groups of patients (group A, n = 59/4657 [1.2%]; group B, n = 75/6748 [1.1%]. Patients from group B were older, obese, diabetic and presented with more peripheral and cerebrovascular disease. Bleeding, gastritis and ulcer with perforation, the most common of these GI events, were associated with the esophagus and stomach (67/147 [45.5%]). Other events that we documented included cholecystitis 10 (6.8%), pancreatitis 13 (8.8%), episodes of small and large bowel ischemia 17 (11.6%), pseudomembranous colitis 12 (8.3%) and diverticulitis 5 (3.4%). Mesenteric ischemia was responsible for 11 (37.9%) of the 29 deaths. Two hundred and ninety-three patients were revascularized without extracorporeal circulation during this study. In this group, we were able to pinpoint 5 (1.7%) GI complications with 3 cases of mesenteric ischemia. Multivariate analysis identified renal insufficiency, prolonged intubation and sepsis as significant, predictive variables of GI complications for the 2 groups of patients whereas the Parsonnet score and stroke were predictive for the second group.

CONCLUSIONS

Although cardiac surgery is now being performed on older patients with significant comorbidity, we could not demonstrate a significant increase of GI complications after cardiac surgery. Off-pump coronary artery bypass does not seem to protect patients from these complications.

Endothelin receptors in cultured and native human radial artery smooth muscle

In human vascular smooth muscle cells endothelin-1, acting at both endothelin A and endothelin B receptors, has been demonstrated to be both a potent vasoconstrictor and mitogen. Our aim was to study the functional expression of endothelin receptors in human radial artery smooth muscle using both native tissue and cultured cells (RASMCs). Radial artery smooth muscle cells were cultured from arterial explants and loaded with the calcium fluorescent dye fura-2. Cells responded to endothelin-1 and a variety of other vasoconstrictors with rises in cytoplasmic calcium ([Ca2+]c). Arterial rings responded to endothelin-1 with an increase in tension. The response of both cells and arterial rings to endothelin-1 was characterized using the selective endothelin A receptor antagonist BQ123 and the endothelin B receptor antagonist BQ788. The RASMCs were found to express [Ca2+]c responses consistent with the expression of only the endothelin A receptor. Endothelin-1-mediated vasoconstriction in radial artery rings was unaffected by BQ788 but was completely blocked by BQ123. Using the selective radioligands [125I]-PD151242 and [125I]-BQ3020 and a combination of in vitro receptor autoradiography and isolated cell preparations, endothelin A receptors were confirmed to be present on RASMCs and on arterial sections, whereas endothelin B binding was barely detectable on native smooth muscle and on RASMCs.

Risk factors for post-cardiopulmonary bypass vasoplegia in patients with preserved left ventricular function

BACKGROUND

Although vasodilatory shock (VS) is one of the main complications of cardiopulmonary bypass (CPB), its pathophysiologic basis remains unclear. The aim of this study was to identify predisposing factors for the development of VS after CPB independent of ventricular function.

METHODS

Thirty-six patients undergoing coronary artery bypass grafting who developed VS were compared with 72 control patients without post-CPB cardiogenic or vasoplegic shock, in a 2:1 case control study. Patients and controls underwent the same anesthetic protocol and were matched by age, sex, operation date, and left ventricle ejection fraction.

RESULTS

Preoperative and intraoperative patient characteristics were not significantly different between the two groups. Preoperative use of angiotensin-converting enzyme inhibitors and intravenous heparin were independent predictors for post-CPB VS by multivariate analysis (relative risk of 2.26 and 2.78, respectively). Intensive care unit stay and hospital stay were significantly longer in VS cases than controls, without any difference in early postoperative mortality.

CONCLUSIONS

The only independent risk factors for postoperative VS identified were preoperative use of angiotensin-converting enzyme inhibitors and intravenous heparin. These risk factors were independent of age, gender, anesthetic protocol, and left ventricle ejection fraction.

Inhibition of vasoconstriction by angiotensin receptor antagonist GR117289C in arterial grafts

BACKGROUND

Angiotensin II (AII) has been suggested to be one of the important factors for genesis of graft spasm in coronary artery bypass surgery. The aim of this work was to investigate the effects of the nonpeptide angiotensin receptor AT1 antagonist GR117289C on the contraction induced by AII and other vasoconstrictors in isolated human internal mammary artery (IMA) preparations.

METHODS

Two hundred eight IMA rings taken from 64 patients undergoing coronary artery bypass grafting were studied in organ baths. The interaction between GR117289C and AII or the other vasoconstrictors (U46619, norepinephrine, endothelin-1, and potassium chloride) was investigated in two ways.

RESULTS

GR117289C induced near-maximal relaxation (94.5% +/- 2.9%) in IMA rings precontracted by AII. In IMA rings incubated with 1 or 10 nmol/L GR117289C, contractile responses to AII were attenuated in a concentration-related manner, whereas the dose-response curve did not shift to the right when higher doses of AII were administered, suggesting that the AT1 receptor blockade was noncompetitive in nature. Moreover, GR117289C also induced significant relaxation (82.9% +/- 8.1%) in IMA rings precontracted by U46619, but no inhibitory responses to U46619 could be observed when IMA rings were incubated with GR117289C. GR117289C did not alter responses to potassium chloride, norepinephrine, and endothelin-1.

CONCLUSIONS

These results indicate that GR117289C is a potent, selective, noncompetitive AT1 receptor antagonist that may have a possible antagonistic effect on the thromboxane A2 receptor. Because AII and thromboxane A2 are important vasoconstrictors in the genesis of graft spasm, GR117289C may become an alternative treatment to relieve graft spasm.

The renin angiotensin system in bypass graft surgery

The renin angiotensin system is implicated in the development of vein graft disease after coronary artery bypass surgery. Components of this system have been shown to play important roles in determining the short-term and long-term performance of coronary artery bypass grafts. Significant differences exist in the commonly used arterial and venous grafts in angiotensin converting enzyme activity and angiotensin responses. The existence of a dual enzyme pathway in angiotensin II formation has also been demonstrated. Such findings have implications for the use of AT1-receptor antagonists over enzyme inhibitors to improve graft performance and prevent the development of coronary artery bypass graft disease.

Better preservation of endothelial function and decreased activation of the fetal renin-angiotensin pathway with the use of pulsatile flow during experimental fetal bypass

OBJECTIVE

Pulsatile flow was shown to overcome the progressive rise in peripheral and placental vascular resistances observed during steady-flow bypass, this rise being counteracted by inhibition of nitric oxide synthase. This study quantifies the release of endothelial vasoactive substances during a 60-minute in utero model of fetal bypass.

METHODS

Fetuses were randomly allocated into 1 of 2 groups (steady flow, n = 8, or pulsatile flow, n = 13) and subjected to bypass through central cannulation and perfusion with either a centrifugal or pulsatile (125 beats x min(-1)) blood pump.

RESULTS

Lactate concentration was high, starting at fetal exteriorization and increasing during fetal preparation in the 2 groups. Once bypass was established, the rise was significant only in the steady-flow group. Plasma nitric oxide metabolites, similar before bypass, reached higher levels during pulsatile flow at the end of bypass (99+/-9 vs. 82+/-23 micromol x L(-1); P =.037). Levels of urinary nitric oxide metabolites were significantly higher in the pulsatile-flow than in the steady-flow group (764+/-143 vs. 508+/-240 micromol x L(-1); P =.005). Plasma cyclic guanosine monophosphate levels increased after 30 minutes of bypass in the pulsatile-flow group (25+/-18 vs. 12+/-8 pmol x mL(-1); P =.004), and urinary cyclic guanosine monophosphate excretion was higher in the pulsatile-flow group (517+/-450 vs. 118+/-78 pmol x mL(-1); P =.024). Plasma endothelin-1 levels increased in the 2 groups and were higher in the steady-flow group at 30 minutes (27+/-5 vs. 23+/-2 pg x mL(-1); P =.04) and 60 minutes of bypass (39+/-7 vs 32 +/- 6 pg x mL(-1); P =.04). Plasma renin concentration increased significantly during bypass only in the steady-flow group (26+/-10 vs. 57+/-42 in ng A1 x mL(-1) x h(-1); P =.04).

CONCLUSIONS

Improved placental and peripheral perfusion during fetal pulsatile-flow bypass may be mediated by preservation of fetal/maternal endothelial nitric oxide biosynthetic mechanisms and/or decreased activation of the fetal renin-angiotensin pathway.

Pulsatile normothermic cardiopulmonary bypass and plasma catecholamine levels

The aim of the study was to assess plasma catecholamine levels in patients undergoing myocardial revascularization and relate them to pulsatile (P) and nonpulsatile (NP) normothermic cardiopulmonary bypass (CPB). Twenty-eight patients were randomly assigned to different CPB management: 15 patients were assigned to group 'P', 13 patients to group 'NP'. During normothermic extracorporeal circulation, group 'P' received pulsatile perfusion, while group 'NP' received nonpulsatile perfusion. Levels of epinephrine and norepinephrine were evaluated during the operation and in the intensive care unit (ICU), at seven time points. Haemodynamic assessment was performed at four time points in the same period. Demographic and surgical data were collected, and the postoperative course was analysed. Epinephrine levels were markedly increased during CPB in both groups, while norepinephrine increased more in group NP in comparison with group P. No significant difference was found in fluid administration, transfusion, drugs usage, or postoperative complications. Normothermic pulsatile CPB seems to achieve reduced levels of norepinephrine. A clinical beneficial effect of this finding was not demonstrated during the study.

Influence of biopump with and without intraaortic balloon on the coronary and carotid flow

BACKGROUND

The objective of this study was to evaluate the influence of biopump used for left ventricular assistance on the coronary and carotid flows in dogs with normal heart. The efficacy of the simultaneous use of an intraaortic balloon pump to compensate the possible deleterious effects of the circulatory assistance with continuous flow was also analyzed.

METHODS

Fifteen dogs were studied. The hemodynamic evaluation included serial measurements of the classic parameters. Carotid and coronary blood flows were obtained by electromagnetic transducers.

RESULTS

The hemodynamic evaluation did not show significant statistical changes. The use of circulatory-isolated assistance with biopump shows reduction (24.6% +/- 6.1%) in coronary flow, in relation to the control situation and the concomitant use of biopump and intraaortic balloon pump showed similar coronary flow. Regarding carotid flow, a similar trend was observed in relation to the positive influence of the pulsatile flow with an intraaortic balloon pump without statistical significance (p = 0.0582).

CONCLUSIONS

The biopump reduces the coronary flow in dogs. The use of intraaortic balloon pump with the biopump increases the coronary flow significantly, reaching similar values to those observed without the circulatory assistance.

Platelets and prostacyclin in arterial bypasses: implications for coronary artery surgery

BACKGROUND

We investigated effects of platelets and prostacyclin formation in human internal mammary (IMA) and radial (RA) arteries.

METHODS

IMA and RA segments were suspended in organ bath with increasing concentrations of platelets. Experiments were applied with and without ketanserin, a 5HT2 receptor antagonist, or U3405, a TXA2 receptor antagonist. The release of prostacyclin (PGI2) was assessed by enzyme immunoassay in vessels without endothelium, before and after contraction with angiotensin (AT) I-II.

RESULTS

In IMA and RA with endothelium, platelets caused contractions, significantly enhanced in arteries without endothelium. Contractions to platelets were higher in RA than in IMA. U3405 reduced the platelet induced contractions in RA but not in IMA. Ketanserin inhibited the platelet induced contractions in IMA and RA. The basal release of PGI2 was more important in IMA than in RA. Addition of AT/I-II significantly reduced the release of PGI2 in IMA but not in RA.

CONCLUSIONS

The RA responds more powerfully to platelets than IMA. Protective system with PGI2 seems to be more powerless in RA than in IMA. This accentuates the importance of antispastic and antiplatelet drugs when arteries are used for coronary artery bypass surgery.

Functional comparison of the human isolated femoral artery, internal mammary artery, gastroepiploic artery, and saphenous vein

Human femoral, internal mammary, and gastroepiploic arteries and saphenous veins are used as bypass grafts for coronary surgery or for reconstruction in arterial occlusive disease. We have characterized the contractile responses of these vessels to various agents that are liberated during cardiac or vascular surgery. In organ baths, U46619 (a stable thromboxane A2 mimetic), norepinephrine, endothelin-1, angiotensin II, and KCl caused concentration-dependent contractions in all vessels tested. Leukotriene C4 did not induce any contraction in the arteries, whereas a contraction was obtained in the saphenous vein rings. U46619 induced the most powerful contraction in all vessels tested. The pD2 values for each agent did not differ among the different vessels. When responses were expressed as a percentage of KCl-induced contraction, the contraction of endothelin-1 (151 ± 5%) and leukotriene C4 (43 ± 5%) was more significant on saphenous veins than on arteries. In conclusion, thromboxane A2 appears to be the most potent endogenous constricting agent on different human vascular beds. Our second finding is that saphenous veins are more sensitive to contract to leukotriene C4 and endothelin-1 than arteries. These properties may influence early and (or) long-term vein graft patency.Key words: femoral arteries, vascular reactivity, thromboxane A2, endothelin-1, leukotrienes.

Angiotensin II concentrations and gut mucosal perfusion in infants undergoing cardiopulmonary bypass

OBJECTIVES

To determine whether hypothermic cardiopulmonary bypass (CPB) per se causes an increase in angiotensin II (A-II) concentration in infants and to investigate the relationship between A-II concentration and gut mucosal perfusion.

DESIGN

Prospective, open, nonrandomized, observational study.

SETTING

Children's teaching hospital.

PARTICIPANTS

Thirty acyanotic infants requiring CPB.

INTERVENTIONS

A-II concentrations were measured on six occasions before, during, and after CPB. An orogastric tonometer allowed intermittent calculations of gastric intramucosal pH (pHi). Gastric mucosal blood flow (flux) was monitored using a laser Doppler flowmeter. Ten infants acted as controls (group 1); 10 infants received captopril, 0.9 mg/kg orally, 45 minutes before induction of anesthesia (group 2), and 10 infants received enalaprilat, 0.06 mg/kg intravenously, just before CPB (group 3).

MEASUREMENTS AND MAIN RESULTS

A-II concentrations were abnormally high in 28 of 30 patients before CPB (median, 450 pg/mL (range, 83 to 5,787 pg/mL). A-II concentrations in groups 1 and 2 decreased during CPB, but values remained at twice normal levels throughout surgery (median, 171 to 198 pg/mL post-CPB). A-II concentrations remained normal (range, 52 to 120 pg/mL) during and after CPB in patients receiving enalaprilat (group 3). The authors found no significant correlation between A-II concentration and pHi or flux before, during, or after surgery.

CONCLUSIONS

Acyanotic infants requiring cardiac surgery may have high perioperative concentrations of A-II. Hypothermic CPB is associated with a decrease in A-II concentration. Reductions in gut mucosal perfusion seen in some infants during hypothermic CPB are not related to increases in A-II concentrations.

Vortex pumping for routine cardiac surgery: a comparative study

Vortex pumping has become popular for mechanical assist applications, but has only recently received serious consideration for use as the arterial pump of choice for routine open-heart surgery. We report on a prospective randomized study designed to evaluate this pump in routine use. Sixteen patients undergoing routine coronary artery surgery were randomized into two groups in which the only difference in equipment and technique was the use of a Stockert roller pump in group S and a Biomedicus vortex pump in group B. The groups were compared with respect to haematology, perioperative fluid balance, transfusion requirements, complement activation, haemolysis and microbubble transmission. The groups were reasonably well matched, with slightly longer mean bypass and ischaemic times in group S (94.8 vs 105.5 minutes and 75.7 and 83.8 minutes respectively). Group B patients showed significant improvements over group S patients with respect to preservation of platelet numbers, decreased complement activation and reduced microbubble transmission. The afterload sensitivity of the vortex pump did not present the perfusionist with any practical problems although a different technique is required for initiating and terminating bypass. We conclude that vortex pumping would seem to offer better blood handling for routine use. More extensive testing is required to establish whether or not this would be reflected in clinically measurable improved patient outcome.

The effect of different bypass flow rates and low-dose dopamine on gut mucosal perfusion and outcome in cardiac surgical patients

The aim of this double-blind, randomized, placebo-controlled trial was to investigate the effects of different cardiopulmonary bypass flow rates and low-dose dopamine on gastric mucosal pH (pHi) and outcome. We hypothesized that by minimizing gut mucosal hypoperfusion during and after cardiac surgery endotoxin translocation may be prevented, resulting in an improved clinical outcome. Four groups of 25 patients each receiving high or low flows during bypass and low-dose dopamine or saline for 24 hours after induction of anaesthesia were studied. The pHi was measured at six time intervals over 24 hours. The combination of low-dose dopamine and a low bypass flow rate was associated with a significantly greater frequency and severity of low pHi. This group also demonstrated a significantly lower vascular resistance on admission to the intensive care unit. There may be an association between low pHi and low vascular resistance.