Critical level of oxygen delivery after cardiopulmonary bypass.

The relationship between oxygen uptake (Vo2) and delivery (Do2) was examined in 64 patients immediately after cardiopulmonary bypass. In 44 patients with lactate levels below 2.5 mmol/L, Vo2 decreased proportionally when Do2 decreased below 300 ml/min X m2. At a Do2 over this level, Vo2 plateaued at 105 +/- 13 (SD) ml/min X m2. In a contrasting group of 22 patients with blood lactate levels above 2.5 mmol/L, Vo2 changes depended on changes in Do2 both alone and below 300 ml/min X m2.