RELATION BETWEEN OXYGEN-CONSUMPTION AND OXYGEN DELIVERY IN PATIENTS AFTER CARDIAC-SURGERY

The relative contributions of oxygen delivery (DO2) and oxygen extract ion (O2ER) to the increase in cellular oxygen uptake (VO2) after cardi opulmonary bypass were studied prospectively in 36 patients after coro nary artery bypass grafting (n = 18), valve replacement (n = 17), and removal of a left atrial tumor (n = 1). VO2 was calculated from the Fi ck equation and DO2 from thermodilution cardiac output and arterial ox ygen content. During the first 24 h after cardiac surgery, there was a strong relation between VO2 and DO2 (VO2 = 28 + 0.27 X DO2, r = 0.79, P < 0.0001) but not between VO2 and oxygen extraction. Mixed venous o xygen saturation (SVO2BAR) was usually reduced when cardiac index was below 2.0 L.min-1.m-2. Patients with a prolonged intensive care unit c ourse (>24 h) had lower cardiac index and lower SVO2 than the other pa tients. Therefore, the progressive increase in VO2 after cardiac surge ry is accomplished primarily by an increase in cardiac output and DO2. It is usually when cardiac function is compromised that O2ER increase s and SVO2BAR decreases.