Circulatory sequelae of administering CPAP in hyperdynamic sepsis are time dependent

Evidence questions the circulation's ability to acutely compensate for abrupt changes in O2 delivery (Qo2). Because both sepsis and continuous positive airway pressure (CPAP) may alter the metabolic regulation of tissue oxygenation, we designed an experiment to determine the interaction, if any, between sepsis and time on circulatory homeostasis after the application of CPAP. Twenty-four sheep were randomized to cecal ligation and perforation (CLP) or sham procedure (Sham) and then rerandomized to receive either CPAP (10 mmHg) or no CPAP (No CPAP; CLP/CPAP, n = 8; CLP/No CPAP, n = 8; Sham/CPAP, n = 4; Sham/No CPAP, n = 4). Forty-eight hours later, CLP animals demonstrated an elevated cardiac index (+63%), systemic Qo2 (+49%), and systemic O2 uptake (+28%). Organ blood flow, measured with radiolabeled microspheres, was augmented to the heart and depressed in organs comprising the splanchnic circulation. Compared with the CLP/No CPAP group and both Sham groups, myocardial Qo2 in the CLP/ CPAP group was significantly elevated when measured both 2 and 8 h after CPAP. These changes were unrelated to differences in mean heart work between the study groups. Simultaneously, QO2 to all of the small gut, large gut, pancreas, and kidney in the CLP/CPAP group was elevated during the 2-h study yet reverted to levels not different from baseline by the 8-h study. These data demonstrate 1) a unique sepsis x time interaction with the use of 10 mmHg of CPAP, particularly in the "nonvital" circulations, and 2) CPAP effects on the septic coronary circulation, which were unexplained by changes in external determinants of myocardial O2 need.