MYOCARDIAL OXYGEN EXTRACTION RATIO IS DECREASED DURING ENDOTOXEMIA INPIGS

Why the myocardial oxygen extraction ratio (ERm) is decreased during s eptic shock in humans is unknown. Therefore, we calculated ERm in 15 a nesthetized pigs by measuring arterial and coronary venous oxygen cont ent. We measured myocardial lactate flux, myocardial contractility, an d global myocardial blood flow and its distribution. After baseline me asurements, animals received either saline (n = 6) or 50 mu g/kg of en dotoxin (n = 9). Measurements were repeated for 4 h. After endotoxin, ERm decreased from 67 +/- 12% at baseline to 36 +/- 10% (P < 0.01) at 1 h and 54 +/- 10% (P < 0.05) at 4 h, associated with an increased myo cardial blood flow that was heterogeneous. Neither myocardial oxygen n or lactate consumption decreased in the endotoxin group, and changes i n left ventricular contractility were not correlated with changes in E Rm. We conclude that the decrease in ERm after endotoxin infusion is d ue to both increased blood flow and mismatching between myocardial oxy gen delivery and demand. Impaired myocardial oxygen extraction capacit y during sepsis did not cause global myocardial tissue hypoxia.