LONG TERM ANGIOTENSIN CONVERTING ENZYME INHIBITOR TREATMENT INCREASES VASOCONSTRICTOR REQUIREMENT DURING NORMOTHERMIC CARDIOPULMONARY BYPASS

Abstract

S74 Introduction: Cardiopulmonary bypass (CPB) results in sympathoadrenal and renin angiotensin system activation due to stress of haemodilution and nonpulsatile perfusion. Systemic vascular resistance (SVR) is lower during normothermic than in hypothermic CPB [1]. Long term use of angiotensin converting enzyme (ACE) inhibitors attenuates effects of catecholamines and thus should lower the SVR further during normothermic CPB, in the absence of hypothermic effects. Methods: After ethical committee approval and informed consent, 37 adult patients for elective cardiac surgery were studied prospectively. The study group of 14 patients were on chronic ACE inhibitor therapy and took the drug on the morning of surgery. The control group of 23 patients were not on any preoperative vasoactive drug therapy. All patients were premedicated with Morphine and Phenargan. GA was induced with Morphine/Diazepam/Thiopentone and maintained with Morphine/Vecuronium/Pancuronium/N (2) O/O2. Bubble oxygenator was used on CPB and perfusate was not cooled but temperature was allowed to drift. Haemodynamics and blood gas parameters were recorded at regular interval. MAP was maintained >50 mmHg with 1 mg increments of phenylepherine, if required, and its use recorded. Haemodynamic values at 10 min. after cross clamp were evaluated with pump flow of 3 L m-2 min-1. Results: The two groups had similar demography, preoperative haemodynamics, CPB haematocrit, oxygen delivery and consumption. Study group showed a significant decrease in MAP and SVR Index on CPB and a significant number required vasconstrictor use to maintain MAP > 50 mm Hg. (Table 1)Table 1Discussion: Long term ACE inhibitor therapy significantly altered haemodynamics during normothermic CPB with a significant number of patients requiring vasoconstrictor use to maintain acceptable perfusion pressures on CPB. In another study, haemodynamic control was not altered during hypothermic CPB despite attenuation of adrenergic response in this group of patients [2]. Extra care should be taken in cardiosurgical patients on ACE inhibitors and the safety of hypothermic CPB extended to this group of patients.