The estimation of calorie needs during routine practice in critically ill patients is highly variable and the thermogenic effect of continuous delivery of enteral nutrition (EN) on overall calorie utilisation in critically ill adults is unknown. The TARGET-ME study is a substudy of the TARGET trial (NCT02306746). The TARGET trial provides the perfect opportunity to measure calorie utilisation via indirect calorimetry (IC) and ventilator-derived carbon dioxide production (VCO2) to compare measured calorie utilisation to estimation methods, determine the potential thermic effect of EN solutions with different energy concentrations and investigate any associations with outcome.

Inclusion Criteria:

Patients must first meet the inclusion and none of the exclusion criteria for the TARGET main trail (NCT02306746). The following additional criteria applies for this study when indirect calorimetry is being used:

• Within 48 hours of randomisation to TARGET (first measurement only)
• Fi02 < 50% for the past 1 hour
• Positive end expiratory pressure (PEEP) < 12 mmHg for the past 1 hour
• The IC test can be conducted within 48 hours of randomisation to TARGET
• The patient is not considered agitated using the usual site assessment
• There is a clinician available to complete the test

Exclusion Criteria:

• There is an air leak in the ventilation circuit (ie bubbling inter-costal catheters, cuff leak at the endotracheal tube
• The patient is receiving renal replacement therapy or extracorporeal membrane oxygenation at the time of measurement
• Has had surgery in the last 6 hours (if enough time within the 48 hour window, consider waiting until this criteria is less than 6 hours)
• If the patient has a traumatic brain injury, for the previous 6 hours, their intracranial pressures have been unstable and in the opinion of the treating intensivist are not controlled
• The treating clinician believes that the IC test will pose risk to the patient

Adult critically ill patients who are mechanically ventilated