Respiratory Quotient and Patterns of Substrate Utilization in Human Sepsis and Trauma

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Abstract
Three hundred measurements of indirect calorimetric and hemodynamic variables were performed in 99 critically ill septic and nonseptic surgical patients. Septics manifested, with respect to nonseptics, higher O2 consumption, metabolic rate and cardiac index, and lower respiratory quotient in the presence of higher glucose infusion rates and glucose infusion rate/metabolic rate ratios. Among septics there was a group of more severely ill patients with signs of multiple organ failure who manifested a dissociated pattern characterized by a tendency to decreased O2 consumption in the presence of increasing cardiac index and central venous O2 partial pressure: they had higher respiratory quotients, with respect to the other septics, for a given glucose infusion rate/metabolic rate ratio. The lower mean respiratory quotient of septics indicates that they depend generally more than nonseptic trauma patients on fat as an energy substrate and confirms a previously obtained evidence of limited hepatic lipogenesis in sepsis. At the same time, however, it is suggested that fat utilization becomes impaired (and hepatic lipogenesis becomes prominent) in sepsis at a stage in which signs of impaired oxidative metabolism and major metabolic abnormalities also develop.