[Effects of clonidine vs trinitroglycerin on myocardial oxygen balance and on pulmonary gas exchange after myocardial revascularization]

Abstract

The authors examined the effects of clonidine, a preferential alpha-adrenergic agonist, upon myocardial oxygen balance and pulmonary function during the perioperative period in patients undergoing CABG surgery. Anesthesia was provided by fentanyl infusion reaching the final dose of 100 micrograms.kg.min-1 in 10 minutes before skin incision. Ten patients received clonidine 0.125 mg intravenously after induction of anesthesia; a group of 10 patients was managed identically except for nitroglycerin infusion during the pre-CPB period, in order to keep the aortic pressure in the normal range. Intergroup differences in hemodynamics, respiratory data, rewarming time, post-operative ST-tract pattern and enzyme values were evaluated. Results are suggestive (in the clonidine group) for ameliorating myocardial oxygen balance by reducing oxygen consumption indexes (systolic aortic pressure, cardiac index, rate pressure product) and increasing coronary blood flow [coronary perfusion pressure (p < 0.01)] at the end of the surgery and intensive care. Global oxygen consumption reduction, recorded in the clonidine group patients, the oxygen available being unchanged, ameliorated the total oxygen balance mainly after sternotomy (p < 0.05) and at the end of bypass (p < 0.05). Cardiac index was greater during the awakening and rewarming period in intensive care and the ventilatory/perfusion ratio was improved, allowing a minor minute ventilation required in clonidine group patients, specially during admission to intensive care.