Intramucosal–arterial PCO2 gap does reflect tissue dysoxia

The fundamental premise of comparable anaerobic states for both groups is based on the presence of oxygen dependence. This premise, however, may not be correct because it appears from the data presented that animals in the HH group did not reach an anaerobic state, and thus were unable to mount increases in ΔPCO2.When calculating oxygen extraction ratios (O2ER) from Fig. 1 of the paper, we find that maximal values for systemic and gut O2ER for the HH group were 48% and 59%, respectively. These values are lower than those reported for critical ERO2 in dogs [2], supporting our contention that animals in the HH group might not have reached a critical oxygen supply condition. Of note, the maximal gut O2ER in the sham control group was 51% – a value not too dissimilar from that in the HH group. Conversely, maximal systemic and gut O2ER levels for the IH group were much higher, at 83% and 90%, respectively, suggesting that these animals experienced greater hypoxic stress.Another parameter that may be used to determine the onset of an anaerobic state is the presence of increased H+ concentration in tissues and blood. Although both groups became acidaemic as oxygen delivery was decreased, it appears that the mechanism responsible for the low pH in the HH group was a respiratory acidosis, not the production of excess H+ by anaerobic tissues. The instillation of hydrochloric acid into the lungs of the HH animals probably produced extensive parenchymal damage and impaired carbon dioxide excretion. This is the probable cause of the low pH and increased PCO2 noted in the HH group.Moreover, we note a decline in bicarbonate from 18.0 to 10.2 mmol/l in the IH group after 90 min of dysoxia. On the other hand, the bicarbonate concentration remained relatively constant at 16.5 and 15.3 mmol/l for the HH group and the control group, respectively. The decline in bicarbonate in the IH group reflects buffering of nonvolatile acids, probably lactic acid. These data again support the notion