Measurement of gastric P_CO2 as an index of tissue hypoxia during obstructive sleep apnea

Background: Gastric mucosal ischemia develops in critically ill patients in a number of clinical settings due to diversion of blood flow from the splanchnic bed to more vital organs, and can be detected by the measurement of gastric intramucosal pH (pHi). Study Objective: We hypothesized that similar changes would occur during obstructive sleep apnea (OSA) due to increased respiratory work during the periods of apnea. Methods: Gastric P_CO2, pHi and arterial blood gases were measured during 3 conditions in 8 patients with severe OSA: at baseline awake, while asleep with ≥30 obstructive apneas or hypopneas per hour, and asleep after elimination of apneas with continuous positive airway pressure (CPAP). Results: Significant changes between the baseline and apnea conditions were detected using ANOVA for repeated measures for gastric P_CO2, 40.2 ± 5.3 vs. 85.4 ± 34.0 (p < 0.001), pHi, 7.41 ± 0.06 vs. 7.11 ± 0.17 (p < 0.005), and the gastric-arterial P_CO2 difference (D_CO2), -2.3 ± 5.5 vs. 44.3 ± 36.21 (p < 0.006). Nasal CPAP returned all measures back to baseline values. Conclusions: Gastric tissue hypoxia develops in patients with severe OSA and may be a marker of disease severity. Treatment of OSA with CPAP eliminates the regional tissue hypoxia.