Increased ileal-mucosal-arterial PCO₂ gap is associated with impaired villus microcirculation in endotoxic pigs

Abstract

Objective: To investigate whether an increased ileal-mucosal-arterial PCO₂ gap (ΔPCO₂) during hyperdynamic porcine endotoxemia is associated with impaired villus microcirculation. Design: Prospective, randomized, controlled, experimental study. Setting: Animal research laboratory. Animals: Twenty-two domestic pigs. Interventions: After baseline measurements, anesthetized and ventilated pigs received continuous i.v. endotoxin (ETX, n=12) for 24 h or placebo (SHAM, n=10). Measurements and results: Before, as well as 12 and 24 h after, the start of endotoxin or saline portal venous blood flow (Q_PV, ultrasound flow probe) and lactate/pyruvate ratios (L/P), the ileal-mucosal-arterial ΔPCO₂ (fiberoptic sensor) and bowel-wall capillary hemoglobin O₂ saturation (%Hb-O₂-cap, remission spectrophotometry) were assessed together with intravital video records of the ileal-mucosal microcirculation (number of perfused/heterogeneously perfused/unperfused villi) using orthogonal polarization spectral imaging (CYTOSCAN A/R) via an ileostomy. At 12 and 24 h endotoxin infusion, about half of the evaluated villi were heterogeneously or unperfused which was paralleled by a progressive significant increase of the ileal-mucosal-arterial ΔPCO₂ and portal venous L/P ratios, whereas Q_PV as well as both the mean %Hb-O₂-cap and the %Hb-O₂-cap frequency distributions remained unchanged. By contrast, in the SHAM-group, mucosal microcirculation was well-preserved, and none of the other parameters were influenced. Conclusions: We conclude that an increased ileal-mucosal-arterial ΔPCO₂ during porcine endotoxemia is related to impaired villus microcirculation. A putative contribution of disturbed cellular oxygen utilization resulting from "cytopathic hypoxia" may also assume importance.