ADVERSE-EFFECTS OF HYPEROXEMIA DURING CARDIOPULMONARY BYPASS

Aiming at elucidating the effects on capillary blood flow and tissue o xygenation of hyperoxemia during cardiopulmonary bypass, we studied sk eletal muscle surface oxygen tensions in 10 patients undergoing electi ve cardiac operations, Methods: In a prospective investigation each pa tient nas exposed to normoxemia (arterial oxygen tension 75 to 115 mm Hg) and hyperoxemia (arterial oxygen tension > 185 mm Hg, inspired oxy gen fraction = 1.00) during normal anesthetized conditions before and after cardiopulmonaly bypass, as well as during normothermic and hypot hermic continuous-flow bypass, In each state hemodynamic variables and arterial and mixed venous blood gas and acid base values were measure d, 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 a t the capillary level, The oxygen distribution profile of such a sampl e is also indicative of capillary blood flow distribution changes, Res ults: In all patients and at each occasion of the investigation marked ly low mean surface oxygen tensions in skeletal muscle were registered , When hyperoxemia was instituted, a significant decrease in these sur face oxygen tensions together with an increase in distribution heterog eneity was seen during all stages, Contrary to prebypass, postbypass, and hypothermic bypass, where vascular resistance, oxygen delivery, an d oxygen consumption remained similar during hyperoxemia and normoxemi a, a significant (p < 0.05) increase in vascular resistance together w ith a decline in oxygen consumption was seen during hyperoxemic normot hermic (35 degrees to 36 degrees C) cardiopulmonary bypass. Conclusion : These findings show that the microcirculatory response to hyperoxemi a, seen under other circumstances, persists during continuous-flow car diopulmonaly bypass, normothermic as well as hypothermic. If these adv erse effects on tissue oxygenation by hyperoxemia can be further verif ied and shown to be valid for other organs than skeletal muscle, we wo uld suggest that hyperoxemia should be avoided, especially during norm othermic cardiopulmonary bypass.