The renin angiotensin aldosterone system during cardiac surgery with morphine nitrous oxide anesthesia

Ten consecutive adult patients undergoing elective cardiac surgery with extracorporeal circulation were anesthetized using morphine (1 to 3 mg/kg) and nitrous oxide. Pre bypass plasma renin activity showed a 3.5 fold elevation (P < 0.001) over baseline values. This correlated with maximal blood pressure elevation. Plasma renin activity remained elevated during bypass. High baseline aldosterone levels increased 3.4 fold (P < 0.001) after 15 min on bypass and 4.0 fold by the end of bypass. Plasma potassium decreased from 3.9 mEq/l before bypass to 3.2 mEq/l (P < 0.001) during bypass, and the fractional urinary excretion of potassium was 32% before bypass with a mean of 34.4% during bypass. Urinary output remained high during bypass despite a progressive decrease in glomerular filtration rate. Catecholamine levels showed no significant change. The data suggest that the renin angiotensin aldosterone system may play a role in blood pressure regulation during cardiopulmonary bypass and may result in the excessive urinary excretion of potassium and decrease in plasma potassium levels.