Inclusion Criteria:  >/= 18 years old. Admitted to the ICU of a participating study site. At least one measurement of energy expenditure performed during ICU stay.  Exclusion Criteria:  Patients readmitted to the ICU of a participating study site >72 hours after ICU discharge and already included in the study (≥1 measurement of energy expenditure performed during prior admission). If a patient is readmitted within ≤72 hours of ICU discharge this is considered a continuation of the last ICU admission for the purposes of this study. Burns >20% of body surface area. Pregnancy.