Abstract
(1) To demonstrate that metabolic parameters are better indicators of tissue hypoxia than regional and whole oxygen consumption (VO(2)). (2) To compare intramucosal pH (pHi) in different gastrointestinal segments. Prospective, interventional study. Research laboratory at a university center. Fourteen anesthetized, mechanically ventilated dogs. Twenty milliliters per kilogram bleeding. 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 PCO(2). We calculated systemic and intestinal oxygen transport (DO(2)) and consumption (VO(2)), pHi and arterial minus intramucosal PCO(2) (DeltaPCO(2)). Then, we bled the dogs and repeated the measurements after 30 min. Systemic and intestinal DO(2) 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 VO(2) 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). During hemorrhage, systemic and intestinal VO(2) remained stable. However, hyperlactatemia and intramucosal acidosis evidenced anaerobic metabolism. pHi changes paralleled in the three intestinal segments.
Highlights
Many studies have analyzed the effects of different types of injury on intestinal oxygenation
Tissue oxygenation monitoring with tonometry, which measures gastrointestinal intramucosal pH, has been reasonably established in recent years [2]
Tonometry has emerged as a useful tool with which to evaluate gut mucosal oxygen metabolism, as blood flow to the stomach and intestine is early and disproportionately reduced in shock and low-flow states
Summary
Many studies have analyzed the effects of different types of injury on intestinal oxygenation. Nelson et al showed that, during progressive bleeding, intestinal oxygen uptake (VO2i) is compromised early, even without changes in systemic VO2 [1]. This limited ability for oxygen extraction makes the intestine suitable to track oxygen metabolism. Tissue oxygenation monitoring with tonometry, which measures gastrointestinal intramucosal pH (pHi), has been reasonably established in recent years [2]. Some studies have analyzed pHi behavior in different segments of the gastrointestinal tract [5, 6], but their results have been inconclusive
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