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 inadequate O-2 delivery, i.e., ''dysoxia.'' However, mucosal PCO2 (Pm-co2) can arise from oxidative phosphorylation, in which case it would detect metabolism that persists as blood stagnates, and/or from HCO3- neutralization by anaerobically produced metabolic acid, in which event it could represent dysoxia. We measured portal venous PCO2 (PVCO2) directly 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, below which PVCO2 and Pm-CO2 diverged strikingly, achieving a final difference of 78.7 +/- 35.81 (SD) Torr. To determine whether PCO2 arose from aerobic or anaerobic metabolism, we used the Dill nomogram to predict venous oxyhemoglobin (HbO(2v)) saturation (%HbO(2v)) from PVCO2. Portal venous %HbO(2) predicted by the Dill nomogram agreed well with measured portal venous %HbO(2) during all but the final values, indicating primarily aerobic appearance of PCO2 in venous blood, suggesting that portions of intestine that remained perfused at very low flow produced dissolved CO2 mainly by oxidative phosphorylation. As Pm-CO2 increased below critical DO2, however, predicted mucosal %HbO(2v) became strikingly negative, achieving a final value of -192 +/- 106.1%, indicating anaerobic dissolved CO2 production in mucosa. We conclude that PCO2 measured in intestinal lumen can be used to detect dysoxia.