Gastric mucosal oxygen delivery decreases during cardiopulmonary bypass despite constant systemic oxygen delivery

Previous studies report a decrease in gastric mucosal oxygen delivery during cardiopulmonary bypass (CPB). However, in these studies, CPB was associated with a reduction in systemic oxygen delivery (DO₂). Conceivably, this decrease in DO₂ could have contributed to the observed decrease in gastric mucosal oxygen delivery. Thus, in the present study, we assessed the effects of the maintenance of DO₂ (at pre-CPB values) during hypothermic (30-32°C) CPB on the gastric mucosal red blood cell flux (GMRBC flux) using laser Doppler flowmetry. In 11 patients requiring cardiac surgery, the pump flow rate during CPB was initially set at 2.4 L · min^-1· m^-2 and was adjusted to maintain DO₂ at pre-CPB values (flow 2.5-2.7 L · min^-1 · m^{- 2}). Despite a constant DO₂, the GMRBC flux was decreased during CPB. These decreases averaged 50% ± 16% after 10 min, 50% ± 18% after 20 min, 49% ± 21% after 30 min, and 49% ± 19% after 40 min of CPB. The rewarming period was associated with an increase in GMRBC flux. Thus, maintaining systemic DO₂ during CPB seems to be an ineffective strategy to improve gastric mucosal oxygen delivery. Implications: In the present study, we tested the hypothesis that gastric mucosal red blood cell flux assessed by laser Doppler flowmetry could be improved by maintaining baseline systemic flow and oxygen delivery during hypothermic cardiopulmonary bypass. Despite this strategy, gastric mucosal red blood cell flux decreased by 50% during hypothermic cardiopulmonary bypass.