CONTINUOUS MONITORING OF MIXED VENOUS OXYGEN-SATURATION FOR DETECTING ALTERATIONS IN CARDIAC-OUTPUT AFTER DISCONTINUATION OF CARDIOPULMONARY BYPASS

Although mixed venous oxygen saturation (S $($) over bar$$ v(o2)) is related to the reciprocal of cardiac output (CO) if both arterial oxygen content and oxygen consumption remain constant, simultaneous alterations in the three variables may occur immediately after discontinuation of cardiopulmonary bypass (CPB). To examine if continuous monitoring of S $($) over bar$$ v (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 S $($) over bar$$ v(O2) cardiac index (Cl), oxygen consumption and haemoglobin concentration in 15 cardiac surgical patients. Changes in S $($) over bar$$ v(O2) correlated well with those in Cl 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 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 S $($) over bar$$ v(O2) did not correlate with either oxygen consumption or haemoglobin concentration. The current results suggest that continuous monitoring of S $($) over bar$$ v(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)