Accuracy of mucosal pH and mucosal-arterial carbon dioxide tension for detecting mesenteric hypoperfusion in acute canine endotoxemia

Objective: To determine the level of mucosal-arterial PCO2 (PCO2 gap) that is both sensitive and specific for the detection of mesenteric hypoperfusio n as defined by either a >50% reduction in portal blood flow or release of lactate by the gut. Design: Animal experiment. Subjects: Seven anesthetized, intubated, mechanically ventilated, and surgi cally instrumented mongrel dogs. Intervention: Escherichia coli endotoxin (1 mg/kg) given intravenously for 5 mins. Measurements and Main Results: Tonometric PCO2, arterial blood gases, arter ial and portal venous lactates, and portal and systemic hemodynamic variabl es were measured, Mucosal pH (pHi) was calculated according to the manufact urers' instructions, From these data, receiver operating characteristics we re calculated, Although animals were resuscitated to maintain a constant ca rdiac output, portal flow decreased from 350 +/- 101 to 152 +/- 75 mL/min ( p < .01) and the gut released lactate into the portal circulation in all an imals. PCO2 gap increased from 13.1 +/- 3.9 to 40.2 +/- 39.2 torr (p < .01) and was inversely correlated with portal blood flow (r(2) = .20; p < .05), For detection of a >50% reduction in portal blood flow, a PCO2 gap of 20 t orr yielded a maximum accuracy of 67% (sensitivity, 55%; specificity, 73%) and was less accurate than a pHi of 7.20, which yielded a maximum accuracy of 76% (sensitivity, 90%; specificity, 70%), although this difference was n ot significant (p = .24), There was also a correlation between pHi and port al blood flow (r(2) = .31; p < .01). For detection of lactate release by th e gut, a PCO2 gap of 20 torr was also 67% accurate (sensitivity, 53%; speci ficity, 78%), whereas a pHi of 7.10 achieved an accuracy of 64% (sensitivit y, 40%; specificity, 83%), which was not significantly different, Conclusion: PCO2 gap measurements are neither sensitive nor specific for me senteric hypoperfusion with regard to total gut blood flow reductions of >5 0% or the release of lactate into the portal circulation.