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.