Identification of the critical oxygen delivery for anaerobic metabolism in critically ill septic and nonseptic humans

Abstract

<h3>Objectives.</h3> —To determine the critical oxygen delivery threshold for anaerobic metabolism and to compare its value between septic and nonseptic critically ill patients. <h3>Design.</h3> —Cohort analytic study, consecutive sample. <h3>Setting.</h3> —Two tertiary care medical and surgical intensive care units in university hospitals. <h3>Patients.</h3> —Nine septic and nine nonseptic critically ill humans. A diagnosis of sepsis was established by the presence of sepsis syndrome, positive cultures obtained within 48 hours of study, and autopsy evidence of a source of infection. <h3>Methods and Interventions.</h3> —The O₂consumption (determined by indirect calorimetry), O₂delivery (calculated from the Fick equation), and concentration of arterial plasma lactate were simultaneously determined at 5-to 20-minute intervals while life support was discontinued. <h3>Main Outcome Measures.</h3> —Critical O₂delivery, critical O₂extraction ratio, and maximal O₂extraction ratio. <h3>Results.</h3> —In all septic and eight nonseptic patients, O₂delivery and O₂consumption displayed a biphasic relationship over the range of O₂delivery studied. There were no differences in critical O₂delivery threshold (3.8±1.5 vs 4.5±1.3 mL·min^-1·kg^-1;<i>P</i>&gt;.28), critical O₂extraction ratio (0.61 ±0.05 vs 0.59±0.16;<i>P</i>&gt;.64), and maximal O₂extraction ratio (0.74±0.08 vs 0.80±0.11;<i>P</i>&gt;.29) between septic and nonseptic patients. These data have greater than 90% power to detect a difference of 2 mL·min^-1·kg^-1in the critical O₂delivery and 0.1 in the critical and maximal O₂extraction ratios between the septic and nonseptic groups. <h3>Conclusions.</h3> —The critical O₂delivery for anaerobic metabolism was identified from the biphasic relationship between O₂delivery and O₂consumption in individual humans. The critical O₂delivery is considerably lower than previously reported in humans with the use of pooled group data. Sepsis does not alter the critical O₂delivery for anaerobic metabolism or tissue O₂extraction ability. Interventions to increase O₂delivery to supranormal levels in critically ill humans in the hope of increasing O₂consumption may be inappropriate. (<i>JAMA</i>. 1993;270:1724-1730)