FM Bloos, HM Morisaki, AM Neal, CM Martin, CG Ellis, WJ Sibbald and ML Pitt
A. C. Burton Vascular Biology Laboratory, Victoria Hospital Research Institute, Ontario, Canada.

This study was undertaken to describe the metabolic O2 reserve of the coronary circulation in an awake sheep model of hyperdynamic sepsis. Forty-eight hours after sheep were randomized to either a SHAM group (n = 8) or a cecal ligation and perforation (CLP) group (n = 8), we measured hemodynamics, organ blood flows, and systemic and myocardial O2 metabolism variables at baseline and through four stages of progressive hypoxia. A significant elevation in arterial lactate levels occurred at a higher O2 delivery in the CLP group (527 +/- 55 ml/min/m2) than in the SHAM group (357 +/- 29 ml/min/m2, p < 0.05). The heart's metabolic O2 reserve (difference in circulatory determinants of O2 availability between baseline and where O2 uptake could not be sustained) was exhausted at an O2 content of 56.9 +/- 4.2 ml O2/L in SHAM sheep and 79.6 +/- 7.2 ml O2/L (p < 0.05) in CLP sheep. An increase in coronary blood flow was three times greater in SHAM than in CLP animals. Myocardial O2 extraction increased in hypoxia in SHAM sheep (0.78 +/- 0.03 to 0.88 +/- 0.02, p < 0.05), but not in CLP sheep (0.79 +/- 0.02 to 0.80 +/- 0.04). We conclude that the metabolic O2 reserve of the coronary circulation is depressed in this model of hyperdynamic sepsis as the ability to increase both coronary blood flows and myocardial O2 extraction was significantly limited.

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