Influence of flow on mucosal-to-arterial carbon dioxide difference

Intramucosal-to-arterial carbon dioxide difference (the so-called PCO2 [partial carbon dioxide tension] gap) remains largely unaltered during decreased oxygen delivery, if the latter is reduced as flow is maintained. In this condition (hypoxic hypoxia or anaemic hypoxia), the PCO2 gap fails to mirror intestinal tissue dysoxia. Results from several experiments have demonstrated that blood flow is the main determinant of PCO2 gap. Gastrointestinal tonometry is clearly a useful indirect method for monitoring perfusion, but it has rather limited value in detecting anaerobic metabolism when blood flow is preserved. These considerations render it very unlikely that PCO2 may dramatically increase (or that intramucosal pH may decrease) in any hypoxic state with preserved flow.