Adverse effects of hyperoxemia during cardiopulmonary bypass

Aiming at elucidating the effects on capillary blood flow and tissue oxygenation of hyperoxemia during cardiopulmonary bypass, we studied skeletal muscle surface oxygen tensions in 10 patients undergoing elective cardiac operations.

In a prospective investigation each patient was exposed to normoxemia (arterial oxygen tension 75 to 115 mm Hg) and hyperoxemia (arterial oxygen tension > 185 mm Hg, inspired oxygen fraction = 1.00) during normal anesthetized conditions before and after cardiopulmonary bypass, as well as during normothermic and hypothermic continuous-flow bypass. In each state hemodynamic variables and arterial and mixed venous blood gas and acid base values were measured. From these data oxygen transport variables were calculated. Tissue oxygenation was studied with the use of a multiple-point polarographic oxygen microelectrode, known to provide measures of oxygen tensions at the capillary level. The oxygen distribution profile of such a sample is also indicative of capillary blood flow distribution changes.

In all patients and at each occasion of the investigation markedly low mean surface oxygen tensions in skeletal muscle were registered. When hyperoxemia was instituted, a significant decrease in these surface oxygen tensions together with an increase in distribution heterogeneity was seen during all stages. Contrary to prebypass, postbypass, and hypothermic bypass, where vascular resistance, oxygen delivery, and oxygen consumption remained similar during hyperoxemia and normoxemia, a significant (p < 0.05) increase in vascular resistance together with a decline in oxygen consumption was seen during hyperoxemic normothermic (35 degrees to 36 degrees C) cardiopulmonary bypass.

These findings show that the microcirculatory response to hyperoxemia, seen under other circumstances, persists during continuous-flow cardiopulmonary bypass, normothermic as well as hypothermic. If these adverse effects on tissue oxygenation by hyperoxemia can be further verified and shown to be valid for other organs than skeletal muscle, we would suggest that hyperoxemia should be avoided, especially during normothermic cardiopulmonary bypass.