Small intestine intramucosal Pco2 and microvascular blood flow during hypoxic and ischemic hypoxia

OBJECTIVE To determine whether small intestine intramucosal Pco2 and mucosal blood flow changes would be different between ischemic and hypoxic hypoxia. DESIGN Randomized animal experiment. SETTING Research laboratory. SUBJECTS Anesthetized, mechanically ventilated, and surgically instrumented pigs. INTERVENTIONS Systemic oxygen delivery was lowered in a stepwise manner to decrease it beyond critical oxygen delivery by lowering either Fio2 or blood volume. MEASUREMENTS AND MAIN RESULTS In hypoxic hypoxia pigs (n = 6), arterial oxygen concentration and oxygen delivery decreases were achieved by progressively reducing arterial Po2 while cardiac index remained unchanged. In ischemic hypoxia pigs (n = 5), oxygen delivery reduction was achieved by progressively reducing cardiac index while arterial Po2 remained unchanged. In control pigs, oxygen delivery remained unchanged. The lowest oxygen delivery measured in both hypoxia and ischemia experiments was 3.60 ± 0.26 vs. 2.93 ± 0.77 mL·kg·min, respectively (p = .23). At the lowest oxygen delivery level, differences between ischemic hypoxia and hypoxic hypoxia experiments were observed for arterial lactate concentration (468 ± 308 vs. 1070 ± 218 mmol/L, respectively;p = .03), mixed venous arterial Pco2 difference (10 ± 7 vs. 4 ± 2 torr, respectively;p = .04), and small intestine mucosal blood flow (6.2 ± 2.1 vs. 15.7 ± 7.4 perfusion units, respectively;p = .02). Small intestine intramucosal-arterial difference was higher in ischemic hypoxia than in hypoxic hypoxia (52 ± 15 vs. 31 ± 12 torr, respectively;p = .03). CONCLUSION Small intestine intramucosal Pco2 increases may indicate systemic oxygen uptake supply limitation in ischemic and hypoxic hypoxia related to conditions of mucosal flow stagnation and CO2 generation.