Myocardial performance early after aorto-coronary bypass surgery and the influence of nitroprusside infusion

The central and peripheral circulation were studied in 12 patients after aortocoronary bypass surgery. During the initial 5 h after termination of cardiopulmonary bypass, the oesophageal temperature rose from 36.5 degrees C to 39.4 degrees C, concomitant with cutaneous vasoconstriction and an increase in systemic vascular resistance (SVR) and mean arterial blood pressure (MABP). The oxygen uptake index (Vo2I) increased by 57% during the rewarming period. The cardiac index (CI), which was constant at 2.8 l.min-1.m-2, was too low to satisfy this oxygen demand and the arterio-venous oxygen content difference (AVDo2) increased to 3.0 mmol . l-1 by the 3rd hour. After 5 h, SVR had decreased and cutaneous vasodilation began. Vo2I and AVDo2 decreased. The postoperative myocardial function was moderately impaired and deteriorated after the cutaneous vasodilation. Twelve patients were given an infusion of sodium nitroprusside during the postoperative period (0.25--2.5 micrograms . kg-1 . min-1). The rewarming pattern was not influenced by this infusion, but the initial increases in MABP and SVR were eliminated. The myocardial performance was better in the nitroprusside group. CI was significantly higher than in the control group (3.5 l.min-1.m-2) and AVDo2 remained normal.