The association among gastric mucosal pH, endotoxemia, and low systemic vascular resistance after cardiopulmonary bypass

Objective: Previously, it was found that a number of patients suffer a 'low systemic vascular resistance syndrome' after cardiopulmonary bypass, and this was hypothesized to be secondary to endotoxemia, resulting from intestinal ischemia during bypass. Design: Prospective cohort. Setting: University teaching hospital. Participants: Thirty-two patients undergoing cardiac surgery. Interventions: A number of variables relating to adequacy of tissue perfusion were measured at seven time periods perioperatively: cardiac output, systemic vascular resistance, oxygen delivery and consumption, oxygen extraction ratio, gastric mucosal pH, serum lactate, and endotoxin levels. Measurements and Main Results: Investigators could not find any association between systemic vascular resistance and mucosal pH or endotoxin levels after bypass. There were significant changes in oxygen flux and extraction ratio (p < 0.001) as well as serum lactate (p < 0.001). There was no significant change in endotoxin levels or mucosal pH. The systemic vascular resistance at 6 hours postbypass could be predicted from the vascular resistance reading at 1 hour postbypass by a regression equation. A significant correlation between systemic vascular resistance and mixed venous oxygen was found at 4 and 6 hours postbypass (p < 0.01) as well as with oxygen extraction (p < 0.01). There was a negative correlation between mucosal pH and serum lactate, particularly at 6 hours postbypass (p < 0.01). There was no correlation between mucosal pH and endotoxin levels, oxygen flux, or cardiac output. Conclusions: The investigators therefore could not find any evidence that intestinal ischemia during bypass, as measured by gastric mucosal pH, predisposes to endotoxemia, or low systemic vascular resistance after cardiac surgery.