Effects of hemorrhage on gastrointestinal oxygenation

Objectives: (1) To demonstrate that metabolic parameters are better indicators of tissue hypoxia than regional and whole oxygen consumption (VO2). (2) To compare intramucosal pH (pHi) in different gastrointestinal segments. Design: Prospective, interventional study. Setting: Research laboratory at a university center. Subjects: Fourteen anesthetized, mechanically ventilated dogs. Interventions: Twenty milliliters per kilogram bleeding. Measurements and main results: We placed pulmonary, aortic and mesenteric venous catheters, and an electromagnetic flow probe in the superior mesenteric artery, and gastric, jejunal and ileal tonometers to measure flows, arterial and venous blood gases and lactate, and intramucosal PCO2. We calculated systemic and intestinal oxygen transport (DO2) and consumption (VO2), pHi and arterial minus intramucosal PCO2 (DeltaPCO(2)). Then, we bled the dogs and repeated the measurements after 30 min. Systemic and intestinal DO2 fell (26.0 +/- 7.3 versus 8.9 +/- 2.6 and 71.9 +/- 17.3 versus 24.6 +/- 9.6 ml/min per kg, respectively, p < 0.0001). Systemic and intestinal VO2 remained unchanged (5.5 +/- 1.3 versus 5.4 +/- 1.3 and 15.7 +/- 5.0 versus 14.9 +/- 5.3 ml/min per kg, respectively). Gastric, jejunal and ileal pHi (7.13 +/- 0.11 versus 6.96 +/- 0.17, 7.18 +/- 0.06 versus 6.97 +/- 0.15, 7.12 +/- 0.11 versus 6.94 +/- 0.14, p < 0.05) and DeltaPCO(2) (21 13 versus 35 23, 15 5 versus 33 16, 23 17 versus 38 20, p < 0.05) changed accordingly. Arterial and mesenteric venous lactate and their difference, rose significantly (1.7 +/- 0.9 versus 3.7 +/- 1.4 and 1.8 +/- 0.8 versus 4.3 +/- 1.5 mmol/l, 0.1 +/- 0.6 versus 0.6 +/- 0.7 mmol/l, p < 0.05). Conclusions: During hemorrhage, systemic and intestinal VO2 remained stable. However, hyperlactatemia and intramucosal acidosis evidenced anaerobic metabolism. pHi changes paralleled in the three intestinal segments.