Effects of postoperative hypertension and its treatment

Hypertension following aorta-coronary bypass operations can contribute to myocardial ischemia. Nitroprusside therapy will reduce afterload, preload, and coronary perfusion pressure. Since both hypertension and its treatment can result in ischemic injury, nitroprusside must be carefully titrated to optimize cardiac function and metabolism. Thirty-one patients undergoing elective coronary bypass grafting were studied during a hypertensive episode (mean arterial pressure [MAP] = 119 +/- 18 mm Hg) and during nitroprusside therapy at an MAP of 97 +/- 11 mm Hg and at an MAP of 80 +/- 11 mm Hg (normotension). Nitroprusside also produced a significant (p less than 0.05) decrease in left atrial pressure (LAP), left ventricular end-diastolic volume index (EDVI) (stroke index divided by ejection fraction by nuclear angiography), stroke index, and stroke work index (SWI). Cardiac lactate extraction (LEx) and the ratio LEx/SWI increased (p less than 0.05) with the initial nitroprusside therapy, but lactate production resulted when the MAP was lowered to 80 mm Hg. Volume loading studies were performed during hypertension in four patients and during nitroprusside therapy in 15 patients. Neither performance nor compliance was significantly altered at an MAP of 97 mm Hg, but compliance decreased at normotension. Both hypertension and its treatment can result in inadequate myocardial metabolism. Nitroprusside should be titrated to maintain MAP between 90 and 100 mm Hg.