Continuous measurement of gut pH with near-infrared spectroscopy during hemorrhagic shock

Background: The rate and magnitude of pH changes in the bowel during hemorrhagic shock are greater than those in the stomach, implying that gastric intramucosal pH may not be a reliable indicator of gut perfusion. Here, we evaluate near-infrared spectroscopy (NIRS) to assess bowel pH in a swine shock model. Methods: Laparotomy was performed to place flow probes, pH microelectrodes, and NIRS probes. Shock was maintained for 45 minutes at a blood pressure of 45 mm Hg, and resuscitation was achieved with shed blood and lactated Ringer's solution to baseline over 60 minutes. Results: Hemodynamic measurements were significantly reduced during shock. Lactic acid peaked during resuscitation and remained elevated. NIRS-measured pH was correlated to electrode-measured pH (R-2 = 0.903 [ischemia] and R-2 = 0.889 [reperfusion]). Estimated measurement accuracy after subject-specific offset correction was 0.083 pH units during ischemia and 0.076 pH units during reperfusion. Conclusion: NIRS determination of small-bowel pH may be a good tool to monitor the adequacy of resuscitation.