ObjectiveTo analyze quantitatively the relationship between sedation and resting energy expenditure or oxygen consumption in postoperative patients.DesignA prospective, clinical study.SettingAn eight-bed intensive care unit at a university hospital.PatientsThirty-two postoperative patients undergoing either esophagectomy or surgery of malignant tumors of the head and neck who required mechanical ventilation and sedation for ≥2 days postoperatively.InterventionsNone.Measurements and Main ResultsA total of 133 metabolic measurements were performed. Ramsay sedation scale (RSS), body temperature, and the dose of midazolam were evaluated at the time of the metabolic cart study. All patients received analgesia with buprenorphine at a fixed dose of 0.625 &mgr;g·kg−1·hr−1continuously. Midazolam was used for induction and maintenance of intravenous sedation after admission to the intensive care unit. The initial dose was 0.04 mg·kg−1·hr−1and was adjusted to achieve a desired depth of sedation at 3, 4, or 5 on the RSS every 4 hrs. The degree of sedation was classified into three states: light sedation (RSS 2–3; n = 49), moderate sedation (RSS 4; n = 39), and heavy sedation (RSS 5–6; n = 45).ResultsWith increasing the depth of sedation, oxygen consumption index (mL·min−1·m−2), resting energy expenditure index (REEI; kcal·day−1·m−2), and REE/basal energy expenditure (BEE) decreased significantly. Oxygen consumption index (mean ± sd), REEI, and REE/BEE were 151 ± 18, 1032 ± 120, and 1.29 ± 0.17 in the light sedation, 139 ± 22, 947 ± 143, and 1.20 ± 0.16 in the moderate sedation, and 125 ± 16, 865 ± 105, and 1.13 ± 0.12 in the heavy sedation, respectively.ConclusionAn increase in the depth of sedation progressively decreases in oxygen consumption index and REEI in postoperative patients.