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

Rozenfeld, Ranna A., Michael K. Dishart, Tor Inge Tønnessen, and Robert Schlichtig. Methods for detecting local intestinal ischemic anaerobic metabolic acidosis by$P{\text{CO}}_2$ . J. Appl. Physiol. 81(4): 1834–1842, 1996.—Gut ischemia is often assessed by computing an imaginary tissue interstitial pH from arterial plasma ${HCO}_3^{-}$ and the$P{\text{CO}}_2$ in a saline-filled balloon tonometer after equilibration with tissue$P{\text{CO}}_2$ (P${\text{ti}}_{{CO}_2}$ ). P${\text{ti}}_{{CO}_2}$ may alternatively be assumed equal to venous$P{\text{CO}}_2$ (${\text{Pv}}_{{CO}_2}$ ) in that region of gut. The idea is that as blood flow decreases, gut P${\text{ti}}_{{CO}_2}$ and${\text{Pv}}_{{CO}_2}$ will increase to the maximum aerobic value, i.e., maximum respiratory${\text{Pv}}_{{CO}_2}$ (${\text{Pv}}_{{CO}_2\hspace{0.5em}\text{rmax}}$ ). Above a “critical” anaerobic threshold, lactate (La⁻) generation, by titration of tissue ${HCO}_3^{-}$ , should raise P${\text{ti}}_{{CO}_2}$ above${\text{Pv}}_{{CO}_2\hspace{0.5em}\text{rmax}}$ . During progressive selective whole intestinal flow reduction in six pentobarbital-anesthetized pigs, we used$P{\text{CO}}_2$ electrodes to test the hypotheses that critical P${\text{ti}}_{{CO}_2}$ is achieved earlier in mucosa than in serosa and that${\text{Pv}}_{{CO}_2\hspace{0.5em}\text{rmax}}$ , computed using an in vitro model, predicts critical P${\text{ti}}_{{CO}_2}$ . We defined critical P${\text{ti}}_{{CO}_2}$ as the inflection of P${\text{ti}}_{{CO}_2}$ -${\text{Pv}}_{{CO}_2}$ vs. O₂ delivery (Q˙o ₂) plots. CriticalQ˙o ₂for O₂ uptake was 12.55 ± 2 ml ⋅ kg⁻¹ ⋅ min⁻¹. Critical P${\text{ti}}_{{CO}_2}$ 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${\text{ti}}_{{CO}_2}$ (129 ± 24 and 96 ± 21 Torr) exceeded${\text{Pv}}_{{CO}_2\hspace{0.5em}...}$