Effect of lipopolysaccharide on intestinal intramucosal hydrogen ion concentration in pigs: evidence of gut ischemia in a normodynamic model of septic shock

We tested the hypothesis that lipopolysaccharide (LPS) leads to an imbalance between mesenteric oxygen delivery (ḊO₂) and gut metabolic demand for oxygen, even when cardiac index (CI) is within the normal range. Two groups of pentobarbital-anesthetized pigs (13 to 17 kg) were studied. The first group (LPS; n = 9) was infused over 20 min with Escherichia coli LPS (100 μg/kg) and resuscitated with normal saline (1.2 ml/kg·min). The second group (NS; n = 5) was not infused with LPS, but was resuscitated in the same way as the LPS group. Superior mesenteric arterial (SMA) blood flow and ileal intramucosal hydrogen ion concentration, [H⁺], were determined using a Doppler-shift probe and a tonometric catheter, respectively. Infusing LPS did not affect CI, although mean arterial pressure and systemic vascular resistance were significantly reduced. SMA flow and mesenteric ḊO₂ decreased significantly in the LPS group. Although mesenteric oxygen utilization was well preserved in both groups, ileal intramucosal [H⁺] was significantly higher in endotoxic animals. These data support the idea that mesenteric oxygen consumption is flow-limited in this clinically relevant porcine model of septic shock.