DISTINGUISHING BETWEEN AEROBIC AND ANAEROBIC APPEARANCE OF DISSOLVED CO2 IN INTESTINE DURING LOW-FLOW

Increased intestinal mucosal PCO2 is used to detect the condition of i nadequate O-2 delivery, i.e., ''dysoxia.'' However, mucosal PCO2 (Pm-c o2) can arise from oxidative phosphorylation, in which case it would d etect metabolism that persists as blood stagnates, and/or from HCO3- n eutralization by anaerobically produced metabolic acid, in which event it could represent dysoxia. We measured portal venous PCO2 (PVCO2) di rectly and Pm-CO2 indirectly with saline-filled CO2-permeable Silastic balloon tonometers in the intestinal lumen during progressive lethal cardiac tamponade in six pentobarbital-anesthetized dogs PVCO2 and Pm- CO2 were relatively constant, differing by similar to 10 Torr until an O-2 delivery (DO2) of similar to 1.3 ml.kg(-1).min(-1) was reached, b elow which PVCO2 and Pm-CO2 diverged strikingly, achieving a final dif ference of 78.7 +/- 35.81 (SD) Torr. To determine whether PCO2 arose f rom aerobic or anaerobic metabolism, we used the Dill nomogram to pred ict venous oxyhemoglobin (HbO(2v)) saturation (%HbO(2v)) from PVCO2. P ortal venous %HbO(2) predicted by the Dill nomogram agreed well with m easured portal venous %HbO(2) during all but the final values, indicat ing primarily aerobic appearance of PCO2 in venous blood, suggesting t hat portions of intestine that remained perfused at very low flow prod uced dissolved CO2 mainly by oxidative phosphorylation. As Pm-CO2 incr eased below critical DO2, however, predicted mucosal %HbO(2v) became s trikingly negative, achieving a final value of -192 +/- 106.1%, indica ting anaerobic dissolved CO2 production in mucosa. We conclude that PC O2 measured in intestinal lumen can be used to detect dysoxia.