Interstitial fluid accumulation does not influence oxygen uptake in the rabbit small intestine.

Abstract

Crystalloid resuscitation increases interstitial fluid volume. Intestinal ischemia and impaired barrier function may contribute to the precipitation of multiple organ failure. Accordingly, the intestine was chosen as target organ to test whether interstitial oedema impairs oxygen extraction by the tissue. The portal vein in anaesthetized rabbits was partially obstructed for 30 min along with an intravenous infusion of 0.9% saline 60-90 ml kg-1 (oedema group, n = 7). Total water content of the small intestine increased from 3.4 ml g-1 dry weight in control (n = 8) to 3.9 ml g-1 in the oedema group (P = 0.049). Small intestinal O2 uptake was calculated from the arteriovenous O2 content and electromagnetic flow measurements in the superior mesenteric artery. Mesenteric flow was reduced stepwise by a snare occluder around the artery. Intestinal oxygenation was monitored indirectly as well, by means of mesenteric venous lactate, arterial base excess and by mucosal pH (pHi) assessed tonometrically. The oxygen extraction ratios were similar in the oedema and control group at similar oxygen supplies. After a 45 min flow reduction to 15% of baseline mesenteric venous lactate and pHi did not differ between the groups. pHi averaged 7.31 and fell to 6.74. Below an intestinal O2 uptake of 2.5 ml min-1, pHi correlated somewhat better with O2 uptake (r = 0.66) than did arterial base excess (r = 0.50). The results indicate that acute elevation of extracellular volume to the extent in the present study, does not impede oxygen uptake in the gut.