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

Although mixed venous oxygen saturation (S $($) over bar$$ v(o2)) is r elated to the reciprocal of cardiac output (CO) if both arterial oxyge n content and oxygen consumption remain constant, simultaneous alterat ions in the three variables may occur immediately after discontinuatio n of cardiopulmonary bypass (CPB). To examine if continuous monitoring of S $($) over bar$$ v (O2) using a fibreoptic pulmonary artery cathe ter would be useful for detecting alterations in CO immediately after discontinuation of CPB, we have examined the relationships between cha nges in S $($) over bar$$ v(O2) cardiac index (Cl), oxygen consumption and haemoglobin concentration in 15 cardiac surgical patients. Change s in S $($) over bar$$ v(O2) correlated well with those in Cl for 60 m in after CPB (r = 0.75, P = 0.0001). A closer correlation between thes e two variables was noted in the patients with baseline Cl of less tha n 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$$ v(O2) did not correlate with either oxygen consumption or haemoglobin concentration. The current results suggest that continu ous monitoring of S $($) over bar$$ v(O2), with the fibreoptic pulmona ry artery catheter may be useful for detecting changes in CO after dis continuation of CPB in patients with compromized cardiac function: (Br . J. Anaesth. 1994; 72: 11-16)