Continuous Measurement of Gut pH with Near-Infrared Spectroscopy during Hemorrhagic Shock

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Abstract
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. 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. Hemodynamic measurements were significantly reduced during shock. Lactic acid peaked during resuscitation and remained elevated. NIRS-measured pH was correlated to electrode-measured pH (R2 = 0.903 [ischemia] and R2 = 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. NIRS determination of small-bowel pH may be a good tool to monitor the adequacy of resuscitation.