Four different gas collection and measurement techniques can be used to perform this test: 
*Douglas Bag: Expired respiratory gases are collected on an inflatable airtight bag. After completion of any test using Douglas Bags, gas collected must be analysed for volume and composition. 
*Canopy (dilution): The dilution technique is considered the gold standard technology for Resting Energy Expenditure measurement in clinical nutrition. The test lasts just few minutes and consists of making a patient lie down relaxed on a bed or on a comfortable couch, with the head under a transparent hood connected to a pump, which applies an adjustable ventilation through it. Exhaled gas dilutes with the fresh air ventilated under the hood and a sample of this mixture is conveyed to the analysers, through a capillary tube and analysed. Ambient and diluted fractions of O and CO are measured for a known ventilation rate, and O consumption and CO production are determined and converted into Resting Energy Expenditure. 
*Face mask (breath by breath): Indirect calorimetry tests are also often performed with a face mask, which is used to convey exhaled and inhaled gas through a turbine flowmeter able to measure the patient's breath by breath minute ventilation, at the same time a sample of gas is conveyed to the analyser and VO and VCO are measured and converted in energy expenditure.
*Interface with a Ventilator (Intensive Care settings): In case the patient is mechanically ventilated, an indirect calorimeter can still measure breath by breath inhaled/exhaled O and CO if interfaced with the ventilator through the endotracheal tube.