Methods for detecting local intestinal ischemic anaerobic metabolic acidosis by P CO 2

Abstract

Rozenfeld, Ranna A., Michael K. Dishart, Tor Inge Tønnessen, and Robert Schlichtig. Methods for detecting local intestinal ischemic anaerobic metabolic acidosis by[Formula: see text]. J. Appl. Physiol. 81(4): 1834–1842, 1996.—Gut ischemia is often assessed by computing an imaginary tissue interstitial pH from arterial plasma [Formula: see text] and the[Formula: see text] in a saline-filled balloon tonometer after equilibration with tissue[Formula: see text](P[Formula: see text]). P[Formula: see text] may alternatively be assumed equal to venous[Formula: see text]([Formula: see text]) in that region of gut. The idea is that as blood flow decreases, gut P[Formula: see text] and[Formula: see text] will increase to the maximum aerobic value, i.e., maximum respiratory[Formula: see text]([Formula: see text]). Above a “critical” anaerobic threshold, lactate (La − ) generation, by titration of tissue [Formula: see text], should raise P[Formula: see text]above[Formula: see text]. During progressive selective whole intestinal flow reduction in six pentobarbital-anesthetized pigs, we used[Formula: see text] electrodes to test the hypotheses that critical P[Formula: see text]is achieved earlier in mucosa than in serosa and that[Formula: see text], computed using an in vitro model, predicts critical P[Formula: see text]. We defined critical P[Formula: see text] as the inflection of P[Formula: see text]-[Formula: see text]vs. O 2 delivery (Q˙o 2 ) plots. CriticalQ˙o 2 for O 2 uptake was 12.55 ± 2 ml ⋅ kg −1 ⋅ min −1 . Critical P[Formula: see text] for mucosa and serosa was achieved at similar whole intestineQ˙o 2 (13.90 ± 5 and 13.36 ± 5 ml ⋅ kg −1 ⋅ min −1 , P = NS). Critical P[Formula: see text] (129 ± 24 and 96 ± 21 Torr) exceeded[Formula: see text](62 ± 3 Torr). During ischemia, La − excretion into portal venous blood was matched by K + excretion, causing [Formula: see text] to increase only slightly, despite P[Formula: see text] rising to 380 ± 46 (mucosa) and 280 ± 38 (serosa) Torr. These results suggest that mucosa and serosa become dysoxic simultaneously, that ischemic dysoxic gut is essentially unperfused, and that in vitro predicted[Formula: see text]underestimates critical P[Formula: see text].