The effect of perfusion flow on oxidative metabolism during cardiopulmonary bypass

The influence of perfusion flow rate on whole-body oxygen consumption (VO2), central venous hemoglobin oxygen saturation (SVO2), and central venous arterial oxygen tension (PVO2) during hypothermic hemodilutional nonpulsatile cardiopulmonary bypass was investigated in 20 patients undergoing coronary artery bypass grafting. In 10 patients, the perfusion flow was 2.4 L.min-1 x m-2 (Group I), whereas a flow of 1.2 L.min-1 x m-2 was used in the other 10 patients (Group II). When the body temperature was 29.7 +/- 1.2 degrees C (Group I) and 29.6 +/- 0.8 degrees C (Group II), mixed venous and arterial blood were sampled simultaneously, and whole-body oxygen consumption was calculated. Data collected during hypothermia were compared with the corresponding values achieved after rewarming to 37 degrees C. In both groups, the whole-body oxygen consumption during hypothermia was lower by about 45% than the VO2 after rewarming. However, SVO2 during the low perfusion flow was not significantly different from SVO2 after rewarming, whereas the temperature-corrected PVO2 was significantly lower. In contrast, the high-perfusion flow provided luxury perfusion as evident by the high SVO2, and maintained the temperature-corrected PVO2 within the normothermic range. Thus, maintenance of the normothermic perfusion flow rate during moderate hypothermic hemodilutional cardiopulmonary bypass may provide a safety margin that may compensate for unexpected increase of oxygen consumption or decrease of oxygen delivery.