Relationship between systemic oxygen supply dependency and gastric intramucosal PCO2 during progressive hemorrhage

Background: As systemic oxygen delivery (DO2) is reduced, oxygen consumption (VO2) is maintained until a critical level is reached (DO(2)crit) below which VO2 becomes supply-dependent and anaerobic metabolism ensues, We examined the relationship between gastric intramucosal PCO2 (PiCO(2)) and, the onset of systemic supply dependency, We also compared PiCO(2) to mixed venous and portal venous blood PCO2 (PmvCO(2) and PpvCO(2)) to assess their utility as premonitory indicators of supply dependency. Methods: Six dogs were subjected to stepwise hemorrhage to effect a progressive decrease in DO2. Inflection points for changes in VO2, PiCO(2), PmvCO(2), and PpvCO(2) versus DO2 were determined, Results: Mean DO(2)crit was 6.0 +/- 0.7 mL.kg(-1).min(-1) whereas the DO2 at which inflection points occurred for PiCO(2) and PpvCO(2) were 13.2 +/- 1.4 and 11.2 +/- 1.5 mL.kg(-1).min(-1), respectively (p < 0.05 for both). Conclusion: Continuous monitoring of PiCO(2) using capnometric recirculating gas tonometry can serve as an early indicator of systemic hypoperfusion before the onset of systemic supply dependency.