Methods for detecting local intestinal ischemic anaerobic metabolic
acidosis by pco2.
Rozenfeld, Ranna A., Michael K. Dishart, Tor Inge T_nnessen, and
Robert Schlichtig.
Departments of Anesthesiology and Critical Care Medicine, Internal
Medicine, and Surgery, University of Pittsburgh, and the Veterans
Affairs Medical Center, University Drive C, Pitttsburgh, PA 15240
APStracts 3:0254A, 1996.
Gut ischemia is often assessed by computing an imaginary tissue
interstitial pH from arterial HCO3- and the PCO2 in a saline filled
balloon tonometer after equilibration with tissue (PtCO2). PtCO2 may
alternatively be assumed equal to venous PCO2 (PvCO2) in that region
of gut. The idea is that, as blood flow decreases, gut PtCO2 and
PvCO2 will increase to the maximum aerobic value, PvmrCO2. Above a
"critical" anaerobic threshold, lactate (La-) generation, by
titrating tissue HCO3-, should raise PtCO2 above PvmrCO2. During
progressive, selective whole intestinal flow reduction in 6
pentobarbital-anesthesthetized pigs, we used PCO2 electrodes to test
the hypotheses that critical PtCO2 is achieved earlier in mucosa than
in serosa, and that PvmrCO2, computed using an in vitro model,
predicts critical PtCO2. We defined critical PtCO2 as the inflection
of PtCO2-PvCO2 vs O2 delivery (QO2) plots. Critical QO2 for VO2 was
12.55 +/- 2 ml.kg-1.min-1. Critical PtCO2 for mucosa and serosa was
achieved at similar whole intestine QO2 (13.90 +/- 5 and 13.36 +/- 5
ml.kg-1.min-1, p = NS). Critical PtCO2 (Torr) values, 129 +/- 24 and
96 +/-21, exceeded PvmrCO2 (62 +/- 3). During ischemia, La- excretion
into portal venous blood was matched by K+ excretion, causing PvCO2
to increase only slightly, despite PtCO2 rising to 380 +/- 46
(mucosa) and 280 +/- 38 (serosa). These results suggest that mucosa
and serosa become dysoxic simultaneously; that ischemic dysoxic gut
is essentially unperfused; and that in vitro-predicted PvmrCO2
underestimates critical PtCO2.
Received 4 November 1994; accepted in final form 13 May 1996.
APS Manuscript Number A1136-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 June 96