Histamine release during adult cardiopulmonary bypass

Histamine, an inflammatory mediator in its own right, may also be a marker for a more widespread systemic inflammatory process. In this study we have examined variations in plasma histamine concentrations produced during the course of cardiac surgery involving cardiopulmonary bypass, the relationship between these variations and intra-operative events. By assays of serum tryptase and CD-63 expression we have also attempted to identify the source of histamine. Histamine concentrations that were significantly raised from baseline level were demonstrated. These were elevated from the time of aortic cross-clamping and continued to be raised for 24 h postoperatively (p < 0.00625). This was associated with an increase in CD-63 expression (p < 0.025) (but not an increase in tryptase concentration) following aortic cross-clamping and protamine administration, suggesting that basophils are the source of histamine. 41% of patients had arrhythmias in the post bypass period. The rise in histamine levels was not related to the incidence of cardiac arrhythmias.

Histamine release during cardiopulmonary bypass in neonates and infants

PURPOSE

Histamine release has been previously documented in adults and children during cardiopulmonary bypass (CPB). It has not been studied in neonates nor during deep hypothermic circulatory arrest (DHCA). Histamine effects could explain many perioperative complications of congenital cardiac surgery such as dysrhythmias and massive oedema. Therefore, documentation of histamine release in the perioperative period is of clinical importance. The source of histamine can be determined by measurement of tryptase which is released with histamine from mast cells but not basophils.

METHODS

Blood samples for histamine and tryptase were taken before and after specific events eg. cross-clamp removal, during anaesthesia and CPB in 14 infants and seven neonates undergoing complex congenital heart repairs and were analysed by commercial radioimmunoassays. Haemodynamic variables and pre and post-op weights were recorded to look for correlation between pathophysiological events and histamine release.

RESULTS

Histamine concentration decreased at the start of bypass (0.69 to 0.38 ng.ml-1 at five minutes, (P < .005). There were no changes associated with DHCA and a small rise with reventilation (P < 0.02). Histamine concentration was lower in neonates than in infants (P < 0.05) during CPB. Plasma histamine and tryptase concentrations did not correlate, suggesting histamine release was from basophils and not from mast cells. Haemodynamic variables did not correlate with histamine concentrations.

CONCLUSION

There was no major histamine release during CPB in infants and neonates. There was no relationship between histamine concentrations and clinical variables. Histamine released during CPB appears to come from basophils and may be a function of age.

Normothermic techniques during open heart operations

There has been considerable interest in the use of normothermic techniques during cardiac operations, both as a means of myocardial protection and as a more physiologic environment for other organs during cardiopulmonary bypass. Although a limited number of uncontrolled studies have suggested superior clinical results compared with conventional hypothermic regimens, these claims have not been thoroughly investigated using randomized protocols. The limited available data suggest that the successful use of warm blood cardioplegia requires adequate delivery of the solution to all parts of the myocardium at optimal flow rates to maintain aerobic arrest, so those who advocate the use of normothermic arrest must pay particular attention to ensure that their myocardial protection is effective. The advantages of employing normothermic systemic perfusion in regard to factors such as improved hemodynamic performance and reduced blood loss postoperatively need to be balanced against concerns regarding the inadequacy of cerebral protection offered by this method.

Determinants of low systemic vascular resistance during cardiopulmonary bypass

Although low systemic vascular resistance occurs during normothermic and hypothermic cardiopulmonary bypass, the determinants of depressed systemic vascular resistance and its effect on outcomes are unknown. To assess the predictors and clinical effects of low systemic vascular resistance, 555 patients undergoing isolated coronary artery bypass grafting were evaluated prospectively. The extent of low systemic vascular resistance during bypass was estimated by the amount of the vasoconstrictor phenylephrine administered: group 1, 0 to 160 micrograms; group 2, 161 to 800 micrograms; group 3, more than 800 micrograms. Multivariate analysis identified bypass temperature, bypass time, and ventricular function as determinants of low systemic vascular resistance. Patients on normothermic bypass accounted for 65% of the patients in group 3 and only 34% of the patients in group 1 (p < 0.0001). The bypass time was longer in the patients in group 3 (97 +/- 28 minutes) than in the patients in group 1 (89 +/- 24 minutes; p < 0.006). Patients with a preoperative left ventricular ejection fraction of 0.40 or less required less phenylephrine during cardiopulmonary bypass (498 +/- 68 micrograms) than did patients with a fraction exceeding 0.40 (1,087 +/- 88 micrograms; p < 0.001). By multivariate analysis, advanced age and the presence of peripheral vascular disease were found to decrease the likelihood of low systemic vascular resistance during normothermic bypass. Diabetes, the left ventricular ejection fraction, the bypass time, and the total cardioplegia infused were found to influence the likelihood of low systemic vascular resistance during hypothermic bypass. Patients in group 3 had a higher cardiac index and lower-mean arterial pressure and systemic vascular resistance postoperatively. In those patients who received a left internal mammary artery graft, the incidences of the low-output syndrome (group 1, 4.9%; group 3, 2.7%; p = not significant) and myocardial infarction (group 1, 1.4%; group 3, 1.8%; p = not significant) were not influenced by the amount of phenylephrine infused during cardiopulmonary bypass. In those patients who were at high risk of suffering a stroke preoperatively, the hypotension induced by the low systemic vascular resistance and its treatment with phenylephrine was not associated with an increased incidence of stroke (group 1, 5.8%; group 3, 2.8%; p = not significant).

A randomized study of the systemic effects of warm heart surgery

The technique of warm heart surgery is defined as continuous warm blood cardioplegia and normothermic cardiopulmonary bypass. Although the systemic effects of traditional myocardial protection are well known, the effects of warm heart surgery are not. In a prospective trial, 204 patients undergoing coronary artery bypass grafting were randomized to the warm heart surgery technique (normothermic group) or traditional intermittent cold blood cardioplegia and cardiopulmonary bypass (hypothermic group). The groups had similar heparin sodium requirement, activated clotting times, urine output, hematocrit, and blood product utilization. There were no differences in hemodynamics immediately after cardiopulmonary bypass. The normothermic patients had a higher incidence of spontaneous defibrillation at cross-clamp removal (84%) than the hypothermic patients (33%) (p less than 0.01). An increase in the flow rate of low K+ cardioplegia was necessary to eradicate electrical activity during aortic occlusion more often in the normothermic patients (20%) than in the hypothermic patients (3%) (p less than 0.01). When low K+ cardioplegia was ineffective, high K+ cardioplegia was necessary to eradicate electrical activity in 31% of the normothermic patients compared with 10% of the hypothermic patients (p less than 0.05). The total cardioplegia volume delivered to the normothermic group (4.7 +/- 1.9 L) was higher than that delivered to the hypothermic group (2.6 +/- 0.8 L) (p less than 0.01). Although urine output was similar in both groups, the serum K+ levels were higher in the normothermic group (5.7 +/- 0.8 mmol/L) than in the hypothermic group (5.3 +/- 0.8 mmol/L) (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)