Oxygen consumption and resting metabolic rate in sepsis, sepsis syndrome, and septic shock

Abstract

Objective: To test the hypothesis that variations in oxygen consumption (VO2) and resting metabolic rate reflect the severity of bacterial infections and reflect the development of sepsis syndrome and septic shock.

Design: Observational study with sequential measurements of VO2 and resting metabolic rate by expiratory gas analysis.

Setting: Medical intensive care unit.

Patients: Thirty patients, treated primarily for presumed bacterial infection, were examined on 118 treatment days.

Interventions: None.

Measurements and main results: VO2 and resting metabolic rate were measured by expiratory gas analysis. For mechanically ventilated patients, a measurement system was developed, based on a paramagnetic oxygen sensor, an infrared CO2 sensor, and digital signal averaging. Measurements in spontaneously breathing patients were performed with a metabolic monitor. Patients were assigned by clinical criteria to the following groups: sepsis, sepsis syndrome, and septic shock. The lowest VO2 value of each patient in each stage was evaluated. Mean VO2 in 15 patients with sepsis was 180 +/- 19 (SD) mL/min/m2, in 11 patients with sepsis syndrome 156 +/- 22 mL/min/m2, and in eight patients with septic shock 120 +/- 27 mL/min/m2 (p < .001). Mean resting metabolic rate in sepsis was +55 +/- 14%, in sepsis syndrome +24 +/- 12%, and in septic shock +2 +/- 24% (p < .001). Mean oxygen delivery (DO2) was 501 +/- 116 mL/min/m2 in sepsis, 515 +/- 186 mL/min/m2 in sepsis syndrome, and 404 +/- 96 mL/min/m2 in septic shock. Oxygen extraction (VO2/DO2) was highest in sepsis (0.39 vs. 0.33 in sepsis syndrome and 0.29 in septic shock). During recovery from sepsis syndrome or septic shock, a significant increase in resting metabolic rate to +61 +/- 22% was measured in nine patients.

Conclusions: In sepsis syndrome, VO2 and resting metabolic rate are enhanced by 30% compared with normal basal metabolism, but they are markedly reduced compared with uncomplicated sepsis. The higher VO2 in uncomplicated sepsis is flow independent. The noninvasive measurement of VO2 and resting metabolic rate by expiratory gas analysis therefore can be used as a quantitative staging and monitoring parameter for the development of sepsis syndrome and septic shock.