Acidosis, catecholamines and cardiovascular dynamics: when does acidosis require correction?

Angiotensin II and Vasopressin for Vasodilatory Shock: A Critical Appraisal of Catecholamine-Sparing Strategies

Vasodilatory shock is a serious medical condition that increases the morbidity and mortality of perioperative and critically ill patients. Norepinephrine is an established first-line therapy for this condition, but at high doses, it may lead to diminishing returns. Oftentimes, secondary noncatecholamine agents are required in those whose hypotension persists. Angiotensin II and vasopressin are both noncatecholamine agents available for the treatment of hypotension in vasodilatory shock. They have distinct modes of action and unique pharmacologic properties when compared to norepinephrine. Angiotensin II and vasopressin have shown promise in certain subsets of the population, such as those with acute kidney injury, high Acute Physiology and Chronic Health Evaluation II scores, or those receiving cardiac surgery. Any benefit from these drugs must be weighed against the risks, as overall mortality has not been shown to decrease mortality in the general population. The aims of this narrative review are to provide insight into the historical use of noncatecholamine vasopressors and to compare and contrast their unique modes of action, physiologic rationale for administration, efficacy, and safety profiles.

Adrenergic Downregulation in Critical Care: Molecular Mechanisms and Therapeutic Evidence

Catecholamines remain the mainstay of therapy for acute cardiovascular dysfunction. However, adrenergic receptors quickly undergo desensitization and downregulation after prolonged stimulation. Moreover, prolonged exposure to high circulating catecholamines levels is associated with several adverse effects on different organ systems. Unfortunately, in critically ill patients, adrenergic downregulation translates into progressive reduction of cardiovascular response to exogenous catecholamine administration, leading to refractory shock. Accordingly, there has been a growing interest in recent years toward use of noncatecholaminergic inotropes and vasopressors. Several studies investigating a wide variety of catecholamine-sparing strategies (eg, levosimendan, vasopressin, β-blockers, steroids, and use of mechanical circulatory support) have been published recently. Use of these agents was associated with improvement in hemodynamics and decreased catecholamine use but without a clear beneficial effect on major clinical outcomes. Accordingly, additional research is needed to define the optimal management of catecholamine-resistant shock.

Catecholamine Vasopressor Support Sparing Strategies in Vasodilatory Shock

Shock syndromes are associated with unacceptably high rates of mortality in critically ill patients despite advances in therapeutic options. Vasodilatory shock is the most common type encountered in the intensive care unit. It is manifested by cardiovascular failure, peripheral vasodilatation, and arterial hypotension leading to tissue hypoperfusion and organ failure. Hemodynamic support is typically initiated with fluid resuscitation strategies and administration of adrenergic vasopressor agents in nonresponsive patients to restore arterial pressure with subsequent adequate organ reperfusion. Unfortunately, high catecholamine dosing requirements may be necessary to achieve targeted hemodynamic goals that may increase the risk of vasopressor-induced adverse events. The purpose of this article is to review the clinical efficacy and safety data and potential role in therapy for catecholamine-sparing agents in vasodilatory shock. Adjunctive therapeutic options to reduce vasoactive support requirements without compromising arterial pressure include arginine vasopressin and analogs, corticosteroids, midodrine, methylene blue, and angiotensin II. Although concomitant vasopressin and corticosteroids have a more defined role in evidence-based guidelines for managing shock, clinicians may consider other potential catecholamine-sparing agents.

Mild metabolic acidosis impairs the β-adrenergic response in isolated human failing myocardium

INTRODUCTION

Pronounced extracellular acidosis reduces both cardiac contractility and the β-adrenergic response. In the past, this was shown in some studies using animal models. However, few data exist regarding how the human end-stage failing myocardium, in which compensatory mechanisms are exhausted, reacts to acute mild metabolic acidosis. The aim of this study was to investigate the effect of mild metabolic acidosis on contractility and the β-adrenergic response of isolated trabeculae from human end-stage failing hearts.

METHODS

Intact isometrically twitching trabeculae isolated from patients with end-stage heart failure were exposed to mild metabolic acidosis (pH 7.20). Trabeculae were stimulated at increasing frequencies and finally exposed to increasing concentrations of isoproterenol (0 to 1 × 10(-6) M).

RESULTS

A mild metabolic acidosis caused a depression in twitch-force amplitude of 26% (12.1 ± 1.9 to 9.0 ± 1.5 mN/mm(2); n = 12; P < 0.01) as compared with pH 7.40. Force-frequency relation measurements yielded no further significant differences of twitch force. At the maximal isoproterenol concentration, the force amplitude was comparable in each of the two groups (pH 7.40 versus pH 7.20). However, the half-maximal effective concentration (EC50) was significantly increased in the acidosis group, with an EC50 of 5.834 × 10(-8) M (confidence interval (CI), 3.48 × 10(-8) to 9.779 × 10(-8); n = 9), compared with the control group, which had an EC50 of 1.056 × 10(-8) M (CI, 2.626 × 10(-9) to 4.243 × 10(-8); n = 10; P < 0.05), indicating an impaired β-adrenergic force response.

CONCLUSIONS

Our data show that mild metabolic acidosis reduces cardiac contractility and significantly impairs the β-adrenergic force response in human failing myocardium. Thus, our results could contribute to the still-controversial discussion about the therapy regimen of acidosis in patients with critical heart failure.

Influence of mild metabolic acidosis on cardiac contractility and isoprenaline response in isolated ovine myocardium

The postoperative course after major surgical procedures such as cardiothoracic operations is often accompanied by acute metabolic abnormalities due to large volume and temperature shifts. In general, those intervention-induced trauma might cause the use of catecholamines to stabilize hemodynamics. Within the cardiac community, there are still controversial discussions about standardized medical therapy to treat postoperative acidosis, for example, buffering versus nonbuffering for improving catecholaminergic response of myocardial contractility. The aim of this study was to investigate the influence of mild (and thus clinically relevant) acidosis on myocardial contractility and catecholamine response in explanted trabeculae of ovine hearts. Intact trabeculae (n = 24) were isolated from the right ventricle of healthy sheep hearts. Two different groups (group 1: pH = 7.40, n = 9 and group 2: pH = 7.20, n = 13) were investigated, and force amplitudes were measured at frequencies between 30 and 180 beats per minute and increasing catecholamine concentrations (isoprenaline 0-3 × 10(-6) mM). Force-frequency relation experiments in the presence of a physiological and/or mild acidotic pH solution showed no significant differences. Mean force amplitudes normalized to the lowest frequency showing no significant differences in force development between 0.5 and 3 Hz (n = 9 vs. 13, P = n.s.) (0.5 Hz absolute values 3.1 ± 2.6 for pH = 7.40 vs. 3.8 ± 2.6 mN/mm(2) for pH = 7.20, P = n.s.). Moreover, there was no significant difference in relaxation kinetics between the two groups. Furthermore, the experiments showed similar catecholamine responses in both groups. Force amplitudes normalized to baseline and maximum force showed no significant differences in force development between baseline and maximum isoprenaline concentrations (n = 6 vs. 9, P = n.s.) (baseline absolute values 4.3 ± 4.0 for pH = 7.40 vs. 3.9 ± 1.2 mN/mm(2) for pH = 7.20, P = n.s.). Additionally, relaxation kinetics did not show differences after catecholamine stimulation. The presented experiments revealed no significant negative inotropic effects on isometrically contracting ovine trabeculae with mild metabolic acidosis (pH = 7.2) compared with physiological pH (7.4). Additionally, similar catecholamine responses were seen in both groups. Further investigations (e.g., in vivo and/or in failing hearts with reduced compensatory reserves) will be necessary to examine optimal medical treatment for metabolic abnormalities after cardiac surgery.

Early adrenaline administration does not improve circulatory recovery during resuscitation from severe asphyxia in newborn piglets

AIM OF THE STUDY

To investigate the effects of early intravenous adrenaline administration on circulatory recovery, cerebral reoxygenation, and plasma catecholamine concentrations, after severe asphyxia-induced bradycardia and hypotension.

METHODS

One-day-old piglets were left in apnoea until heart rate and mean arterial pressure were less than 50 min(-1) and 25 mmHg, respectively. They randomly received adrenaline, 10 μgkg(-1) (n=16) or placebo (n=15) and were resuscitated with air ventilation and, when needed, closed-chest cardiac massage (CCCM). Eight not asphyxiated animals served as time controls.

RESULTS

CCCM was required in 13 piglets given adrenaline and in 13 given placebo. Time to return of spontaneous circulation was: 72 (66-85)s vs. 77 (64-178)s [median (quartile range)] (p=0.35). Time until cerebral regional oxygen saturation (CrSO(2)) had increased to 30% was 86 (79-152)s vs. 126 (88-309)s (p=0.30). The two groups did not differ significantly in CrSO(2), heart rate, arterial pressure, right common carotid artery blood flow, or number of survivors: 13 vs. 11 animals. Plasma concentration of adrenaline, 2.5 min after resuming ventilation, was 498 (268-868)nmoll(-1) vs. 114 (80-306)nmoll(-1) (p=0.01). Corresponding noradrenaline concentrations were 1799 (1058-4182)nmoll(-1)vs. 1385 (696-3118)nmoll(-1) (ns). In the time controls, the concentrations were 0.4 (0.2-0.6)nmoll(-1) of adrenaline and 1.8 (1.3-2.4)nmoll(-1) of noradrenaline.

CONCLUSION

The high endogenous catecholamine levels, especially those of noradrenaline, may explain why early administered adrenaline did not significantly improve resuscitation outcome.

Contractile action of levosimendan and epinephrine during acidosis

We evaluated the inotropic actions of levosimendan and epinephrine, both singly and in combination, under isohydric (pH 7.4) and acidotic (pH 7.0) conditions in isolated guinea-pig hearts. Acidosis depressed contractility and myocardial relaxation by 25-30%, and both inotropes were less efficacious at pH 7.0, while their potencies were unaffected. In combination experiments, the presence of levosimendan increased the potency of epinephrine approximately 17-fold (pH 7.4) and 11-fold (pH 7.0), and the presence of epinephrine increased the potency of levosimendan approximately 12-fold (pH 7.4) and approximately 21-fold (pH 7.0). At pH 7.0, both inotropes augmented papillary muscle contraction to a similar extent, but in contrast to epinephrine, levosimendan non-significantly [corrected] raised cAMP levels. In conclusion, combining levosimendan with epinephrine helps to overcome the depressed inotropic actions of epinephrine during acidosis, suggesting that additional studies which might justify clinical evaluation of the concurrent use of the two agents should be performed.

An evidence-based evaluation of the use of sodium bicarbonate during cardiopulmonary resuscitation

The use of bicarbonate is rooted in three decades of clinical experience and observational studies. For many years, bicarbonate passed the tried and true test for clinical therapies; however, administration of sodium bicarbonate during cardiac arrest and hypoxic acidosis has become increasingly controversial. The controversy provides an excellent opportunity to evaluate the impact an evidence-based approach might have on a common clinical practice. Is bicarbonate efficacious in the treatment of the severe acidosis that accompanies cardiac arrest during cardiopulmonary resuscitation (CPR)? Are the deleterious effects of bicarbonate clinically relevant? What is the evidence upon which a rational decision may be based? This review evaluates and ranks the evidence supporting the use of sodium bicarbonate in the therapy of acidosis associated with cardiac arrest during CPR.

Acute haemodynamic effects of sodium bicarbonate administration in respiratory and metabolic acidosis in anaesthetized dogs

Twenty-seven halothane-anaesthetized, mechanically ventilated adult mongrel dogs were randomly assigned to either respiratory acidosis group [pHa 7.22 (0.03, SD), PaCO2 9.6 (1.1) kPa, base excess -0.5 (1.4) mmol.l-1, n = 9], metabolic acidosis group [pHa 7.20 (0.05), PaCO2 5.5 (0.4) kPa, base excess -11.1 (2.1) mmol.l-1, n = 9], or nonacidosis group [pHa 7.37 (0.07), PaCO2 5.2 (0.4) kPa, base excess -1.1 (1.5) mmol.l-1, n = 9]. Respiratory acidosis and metabolic acidosis were induced by decreasing respiratory rate and continuous infusion of 2 mmol.l-1 hydrochloric acid, respectively. Sodium bicarbonate solution 1 mmol.kg-1 was injected into the right atrium over five seconds when haemodynamic stability was obtained. In all three groups, acute administration of sodium bicarbonate produced transient decreases in mean arterial pressure and RV dP/dtmax, and transient increase in right atrial pressure 30 seconds after injections, but these variables returned to the pre-injection values by the end of the three minutes observation period. Although no significant differences were seen in haemodynamic variables among the three groups at 30 seconds, one and three minutes, maximum reductions in both RV dP/dtmax and PBF in the metabolic acidosis group (260 (143) mmHg.s-1 and 0.38 (0.26) l.min-1) were significantly greater than those in the non-acidosis group (127 (34) mmHg.s-1 and 0.08 (0.09) l.min-1; P < 0.05).

Extramyocardial acidosis impairs cardiac resuscitability in isolated, perfused, rat hearts

OBJECTIVES

Patients suffering out-of-hospital cardiac arrest have various degrees of acidemia when cardiopulmonary resuscitation is initiated. Myocardial hypercarbia, rather than decreases in myocardial pH, may determine cardiac resuscitability. Accordingly, we questioned whether different degrees of acidemia accompanying cardiac arrest affect cardiac resuscitability. We evaluated the effect of different degrees of extramyocardial acidosis on cardiac performance and resuscitability after ventricular fibrillation using isolated, perfused, rat hearts.

DESIGN

Prospective, randomized, controlled study.

SETTING

Experimental animal laboratory in a university hospital.

SUBJECTS

Thirty-one male, Sprague-Dawley rats.

INTERVENTIONS

Rat hearts were perfused with N-[2-hydroxyethyl]piperazine-N-[2-ethanesulfonic acid] (HEPES) buffered solution (sodium chloride 145 mM, potassium chloride 4 mM, sodium dihydrogen phosphate dihydrate 1.25 mM, magnesium chloride 1.5 mM, calcium chloride 2 mM, HEPES 6 mM, glucose 10 mM), which was bubbled with 100% oxygen and adjusted to a pH of 7.4. The perfusion pressure was held constant at 60 mm Hg. After 60 mins of stabilization, the control perfusion solution was switched to one of the solutions titrated to pH 6.2, 6.5, 6.8, 7.1, or 7.4, using 1 N of sodium hydroxide. Hearts were allocated randomly to each group. After 15 mins of perfusion, the perfusion was discontinued, and artificial ventricular fibrillation was induced by electrical stimulation for 5 mins. The hearts were then perfused again in one of the same acidotic solutions for 30 mins.

MEASUREMENTS AND MAIN RESULTS

Left ventricular developed pressure (left ventricular pressure minus end-diastolic left ventricular pressure), positive change in left ventricular pressure over time, heart rate (HR), and coronary flow were continuously measured. After 60 mins of stabilization, the values of left ventricular developed pressure, positive change in left ventricular pressure over time, HR, and coronary flow were not significantly different between groups. After 5 mins of ventricular fibrillation, all hearts were asystolic and left ventricular developed pressure, positive change in left ventricular pressure over time, HR, and coronary flow were all zero. After 30 mins of reperfusion, all values in the acidotic groups were significantly lower than the values in the pH 7.4 group. When we judged the recovery of left ventricular developed pressure at > 35 mm Hg as "resuscitated," resuscitability was impaired at a pH of < 7.1. No hearts recovered after perfusion below a pH of 6.5.

CONCLUSIONS

Extramyocardial acidosis below pH 7.1 decreased cardiac performance and resuscitability after ventricular fibrillation. This result indicates that progressive acidemia during cardiac arrest is one of the important determinants of cardiac resuscitability.

Effect of pH and lidocaine on beta-adrenergic receptor binding. Interaction during resuscitation?

Epinephrine and other beta-adrenergic receptor (beta AR) agonists are often administered during cardiopulmonary resuscitation, a time when acid-base abnormalities and arrhythmias also commonly occur. We tested whether beta 2AR binding is influenced by pH or the antiarrhythmic drug lidocaine, and whether pH might influence the interaction of lidocaine with beta 2ARs. With institutional review board approval and informed consent, 32 venous blood samples were obtained from volunteers. Lymphocytes (which bear beta 2ARs similar to those found in heart) were isolated by density gradient centrifugation. Specific binding of the beta AR ligand 3H-dihydroalprenolol (3H-DHA) was determined with lidocaine concentrations ranging from 10(-6) to 10(-2) mol/L (n = 18 experiments), and with and without lidocaine (n = 10 experiments), 100 mumol/L, and with and without QX314 (a permanently charged lidocaine derivative), 1 mmol/L (n = 4 experiments). Data are presented as percent of control-specific binding measured at a pH of 7.4. Statistical analysis consisted of Spearman's rank-test. 3H-DHA-specific binding increased (p < .001) with pH. Thus, alkaline conditions favored binding of 3H-DHA to the receptor. Lidocaine inhibited 3H-DHA binding to beta 2ARs in a concentration-dependent manner. The concentration that inhibited specific binding of 3H-DHA by 50% was 3.1 x 10(-4) mol/L (95% confidence limits, 1.3 x 10(-4) to 7.5 x 10(-4) mol/L). Lidocaine potency at inhibiting beta 2AR binding also increased with increasing pH; thus, there was limited benefit (in terms of increasing binding to beta 2ARs) to increasing pH when lidocaine was present. QX314, despite being present in a 10-fold greater concentration than lidocaine, had no effect on 3H-DHA binding at any tested pH. The affinity of beta 2 ARs for both 3H-DHA and lidocaine increased with pH. Thus, the response to beta 2AR agonists (when no lidocaine is present) might be expected to be greater with normal or alkalotic pH than under acidotic conditions, supporting the correction of metabolic acidosis to achieve optimal effects from beta 2AR agonists during resuscitation.

Norepinephrine-induced hypertension following cardiac arrest: effects on myocardial oxygen use in a swine model

STUDY OBJECTIVE

Recent studies suggest that norepinephrine-induced hypertension early after cardiac arrest ameliorates cerebral hypoperfusion and improves neurologic outcome. The purpose of this study was to evaluate the effects of early norepinephrine-induced hypertension on postresuscitation myocardial blood flow and oxygen use.

DESIGN

Prospective, controlled laboratory study.

PARTICIPANTS

Ten swine.

INTERVENTIONS

All animals underwent 10 minutes of ventricular fibrillation cardiac arrest followed by 5 minutes of low-flow cardiopulmonary bypass (10 mL/kg.min), norepinephrine (0.12 mg/kg), and defibrillation. Animals then were assigned to a hypertension group (mean aortic pressure, 95 mm Hg) or a control group (mean aortic pressure, 75 mm Hg) by titrating a norepinephrine infusion to attain the prescribed aortic pressure.

RESULTS

Myocardial blood flow, perfusion pressure, and oxygen metabolism were compared between groups at different times using analysis of variance with a post-hoc Tukey test. Groups had similar myocardial blood flow during ventricular fibrillation, total defibrillation energy, and time to restoration of spontaneous circulation. Fifteen minutes after restoration of spontaneous circulation, the hypertension group had significantly elevated myocardial blood flow, 965 +/- 314 mL/min.100 g versus 325 +/- 67 mL/min.100 g in the control group (P < .001), myocardial oxygen consumption of 51.2 +/- 26.9 mL O2/min.100 g versus 6.4 +/- 3.4 mL O2/min.100 g (P < .001), and myocardial oxygen extraction of 46% +/- 20% versus 14% +/- 4% (P < .01).

CONCLUSION

In the early resuscitation period, increasing the norepinephrine dose to induce mild hypertension significantly increases oxygen use in the postischemic myocardium.

Guidelines for paediatric life support. Paediatric Life Support Working Party of the European Resuscitation Council

The paediatric life support working party of the European Resuscitation Council was set up in 1992 with the aim of producing guidelines for basic and advanced paediatric resuscitation that would be acceptable throughout Europe. The commonest cause of cardiac arrest in children is problems with the airway. The resulting difficulties in breathing and the associated hypoxia rapidly cause a severe bradycardia or asystole. In contrast, adults have primary cardiac events resulting in ventricular fibrillation. This important difference in the pathogenesis of paediatric and adult cardiac arrest is reflected in these European Resuscitation Council guidelines, which complement those already published for adults.

Sodium bicarbonate versus Carbicarb in canine myocardial hypercarbic acidosis

The objective of this study was to compare the in vivo effects of sodium bicarbonate (NaHCO3) and Carbicarb infusion on regional contractile performance and acid-base status in the setting of hypercarbic acidosis. Animals (N = 9) were anesthetized and paralyzed using sodium pentothal, halothane, and pancuronium bromide, and mechanically ventilated with an air-O2 mixture so that arterial PO2 was > or = 300 mm Hg. Following beta-adrenergic blockade, alveolar ventilation was gradually reduced over a 50-minute period to increase arterial PCO2 to 60 to 80 mm Hg. Each of the following solutions was then infused in consecutive order directly into the left anterior descending artery coronary artery for 15 minutes: (1) 8.4% NaHCO3 at 2 mL/min; (2) 5% sodium chloride at 2 mL/min, equivalent to NaHCO3 in osmolality; (3) 6.3% Carbicarb at 0.5 mL/min, equivalent to NaHCO3 in buffer capacity; and (4) 6.3% Carbicarb at 2 mL/min, equivalent to NaHCO3 in volume. Regional stroke work analog (ultrasonic dimension transducers), interstitial myocardial pH (Khuri electrode), coronary blood flow (doppler flow probe), and hemodynamic/metabolic variables (heart rate, blood pressure, arterial and coronary venous blood gases) were measured at 1, 5, 10, and 15 minutes during each infusion and 10 minutes after the infusion was discontinued, ie, at 25 minutes. Animals were allowed to recover for 45 minutes between interventions. Values at each time point were compared with baseline for statistical significance. Small reductions in interstitial myocardial pH (P < .05) and stroke work (P > .05) were observed within 1 minute of NaHCO3 administration. Both parameters increased significantly from baseline levels thereafter, ie, interstitial myocardial pH at 5 minutes and stroke work at 15 minutes. Infusion of Carbicarb invariably was associated with an increase (P < .05) in interstitial myocardial pH. Stroke work increased (P < .05) during low-dose Carbicarb administration, but infusion of the higher dose was accompanied by a biphasic response, ie, an increase (P < .05) from 0 to 5 minutes, followed by a gradual decrease that achieved statistical significance 10 minutes after termination of the infusion. End-diastolic length was inversely proportional to changes in stroke work, and coronary blood flow varied directly with changes in coronary venous Pco2. Myocardial O2 consumption decreased (P < .05) during Carbicarb infusion, but changes during NaHCO3 did not reach statistical significance. Our findings lend support to the hypothesis that intramyocardial pH determines myocardial function independent of CO2 production by buffer therapy.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of metabolic acidosis and alkalosis on the response to sympathomimetic drugs in dogs

Sympathomimetic drugs are commonly used in many circumstances to increase cardiac output, blood pressure, and myocardial contractility. However, factors such as acidosis or alkalosis are known to influence the action of these drugs. This study looked at the response to the administration of epinephrine, norepinephrine, dopamine, dobutamine, isoproterenol, and glucagon at normal pH and under acidotic (pH 7.2 +/- 0.01) and alkalotic (pH 7.59 +/- 0.01) conditions in 17 dogs. Acidosis was produced with an infusion of hydrochloric acid and alkalosis by infusion of sodium bicarbonate. The infusions were given over one hour followed by a 15- to 30-minute stabilization period. With the administration of each sympathomimetic drug at each pH level, hemodynamic parameters and measurements of myocardia; contractility were recorded. Epinephrine increased cardiac output at normal pH, but decreased cardiac output under conditions of both acidosis and alkalosis; the net change from values at pH 7.40 was nearly 3 L/min. The only other drug to demonstrate this reversal of cardiac output, though to a lesser degree, was dopamine, 10 microg/kg/min, and only in the alkalotic state. Dobutamine was the only drug that decreased contractility under acidotic conditions, while all other drugs caused an increase. In sum, epinephrine was the only drug markedly affected by metabolic acidosis and alkalosis. Isoproterenol's hemodynamic effects were altered the least by changes in acid-base balance. Alkalosis had an equally adverse effect on the cardiovascular system as compared with acidosis.

Is the Use of Calcium Helpful in Cardiac Resuscitation? Experimental and Clinical Studies

The effect of positive inotropic agents on circulation and ventricular fibrillation threshold are not fully understood during the influence of metabolic acidosis during circulatory arrest. This is the same case with alkalosis, caused by the over-correction of sodium bicarbonate. Furthermore, the role of calcium during CPR is not clear.

Therefore, we investigated the influence of metabolic acidosis and alkalosis with and without the administration of the positive inotropic substances epinephrine and calcium upon contractility and ventricular fibrillation threshold.

Current management of patients after cardiopulmonary bypass

The postoperative management of cardiac surgical patients is reviewed with particular reference to some of the recent advances and current controversies. It is emphasised that there has been a marked decrease in the incidence of many of the major problems associated with cardiopulmonary bypass and that, in the majority of cases, cardiac surgery is now a routine procedure associated with a very low morbidity and mortality.

Sequential patterns of haemodynamic and metabolic changes in experimental hypovolaemic shock. II. Responses to reinfusion of shed blood

The haemodynamic and metabolic effects which follow the infusion of blood in experimental hypovolaemia have not been studied in detail. The 10 dogs that survived 90 min of hypovolaemia in a study of bleeding (Pardy and Dudley, 1979) were investigated during and shortly after the reinfusion of shed blood using the same techniques. Data from 9 animals were suitable for analysis. As with bleeding, 6 sequential phases were identified; reinfusion of blood was completed in the fifth phase. Initial reinfusion was associated with a rapid improvement in haemodynamic and metabolic status, although mean arterial pH fell because carbon dioxide production increased. Maximum metabolically effective tissue perfusion was probably attained in phase II, but haemodynamic improvement continued until phase IV. Arterial pH did not rise above the pre-infusion value until phase V, and this rise was the result of a fall in PaCO2 secondary to a reduction in physiological dead space and an increase in buffering capacity. Pulmonary artery pressure was superior to systemic artery pressure as a predictor of cardiac output during blood volume restoration. A number of conclusions pertaining to clinical practice are drawn.