Association between oxygen delivery and consumption in patients undergoing cardiac surgery. Is there supply dependence?

Abstract

We studied the relationship between oxygen delivery (DO2) and consumption (VO2) in twenty patients undergoing cardiac surgery, in order to determine if VO2 was dependent on DO2 (pathological oxygen supply dependence). We measured VO2 from expired gas analysis (VO(2G)) and compared this to that calculated using the reverse Fick method (VO(2F)). Both VO(2G) and VO(2F) increased after cardiopulmonary bypass (P < 0.001, without change in DO2 (i.e. oxygen extraction ratio increased). There was a significant relationship between changes in DO2 and VO(2F), both before bypass (r = 0.74, P < 0.001) and after bypass (r = 0.69, P < 0.001), while changes in DO2 and VO(2G) had no such relationship (pre-bypass: r = 0.38, P = 0.094; post-bypass: r = 0.10, P = 0.68). There was poor agreement between VO(2F) and VO(2G) perioperatively. We could not demonstrate supply dependence in elective cardiac surgical patients.