Continuous monitoring of mixed venous oxygen saturation for detecting alterations in cardiac output after discontinuation of cardiopulmonary bypass

Abstract

Although mixed venous oxygen saturation (Sv¯o2) is related to the reciprocal of cardiac output (CO) if both arterial oxygen content and oxygen con sumption remain constant, simultaneous alterations in the three variables may occur immediately after discontinuation of cardiopulmonary bypass (CPB). To examine if continuous monitoring of Sv¯o2, using a fibreoptic pulmonary artery catheter would be useful for detecting alterations in CO immediately after discontinuation of CPB, we have examined the relationships between changes in Sv¯o2 cardiac index (Cl), oxygen consumption and haemoglobin concentration in 15 cardiac surgical patients. Changes in Sv¯o2 correlated well with those in Cl for 60 mm after CPB (r = 0.75, P = 0.0001). A closer correlation between these two variables was noted in the patients with baseline Cl of less than 2 litre min-1 m-2 (r = 0.87) than the patients with baseline Cl of more than 2 litre min-1 m-2 (r = 0.66). However, changes in Sv¯o2 did not correlate with either oxygen consumption or haernoglobin concentra tion. The current results suggest that continuous monitoring of Sv¯o2 with the fibreoptic pulmonary artery catheter may be useful for detecting changes in CO after discontinuation of CPB in patients with compromized cardiac function: (Br. J. Anaesth. 1994; 72: 11-16) © 1994 British Journal of Anaesthesia.