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

Although mixed venous oxygen saturation (SVO2) is related to the reciprocal of cardiac output (CO) if both arterial oxygen content and oxygen consumption remain constant, simultaneous alterations in the three variables may occur immediately after discontinuation of cardiopulmonary bypass (CPB). To examine if continuous monitoring of SVO2 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 SVO2, cardiac index (CI), oxygen consumption and haemoglobin concentration in 15 cardiac surgical patients. Changes in SVO2 correlated well with those in CI for 60 min after CPB (r = 0.75, P = 0.0001). A closer correlation between these two variables was noted in the patients with baseline CI of less than 2 litre min-1 m-2 (r = 0.87) than the patients with baseline CI of more than 2 litre min-1 m-2 (r = 0.66). However, changes in SVO2 did not correlate with either oxygen consumption or haemoglobin concentration. The current results suggest that continuous monitoring of SVO2 with the fibreoptic pulmonary artery catheter may be useful for detecting changes in CO after discontinuation of CPB in patients with compromised cardiac function.