Indirect calorimetry
Indirect calorimetry calculates
Scientific background
Indirect calorimetry measures O2 and nitrogen consumption and CO2 production. On the assumption that all the oxygen is used to
where RQ is the respiratory quotient (ratio of volume CO2 produced to volume of O2 consumed), is 21.13 kilojoules (5.05 kcal), the heat released per litre of oxygen by the oxidation of carbohydrate, and is 19.62 kilojoules (4.69 kcal), the value for fat. This gives the same result as the Weir formula at RQ = 1 (burning only carbohydrates), and almost the same value at RQ = 0.7 (burning only fat).
History
Antoine Lavoisier noted in 1780 that heat production, in some cases, can be predicted from oxygen consumption[citation needed], using multiple regression. Indirect calorimetry, as we know it, was developed around 1900 as an application of thermodynamics to animal life.[6] Although the development of indirect calorimetry dates back over 200 years, its greatest use has been in the last two decades with the development of total parenteral nutrition, interdisciplinary nutrition support teams, and the production of portable, reliable, relatively inexpensive calorimeters.[7]
Collection methods
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.[8] 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.[3] 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 O2 and CO2 are measured for a known ventilation rate, and O2 consumption and CO2 production are determined and converted into Resting Energy Expenditure.[9]
- 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 VO2 and VCO2 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 O2 and CO2 if interfaced with the ventilator through the endotracheal tube.
Applications
Indirect calorimetry provides at least two pieces of information: a measure of energy expenditure or 24-hour caloric requirements as reflected by the
References
- ^ a b Ferrannini E."The theoretical bases of indirect calorimetry: a review." Metabolism. 1988 Mar;37(3):287-301.
- ^ Marson F, et al. "Correlation between oxygen consumption calculated using Fick's method and measured with indirect calorimetry in critically ill patients." Arq Bras Cardiol. 2004 Jan;82(1):77-81, 72-6. Epub 2004 Feb 12.
- ^ a b Haugen HA, et al. "Indirect calorimetry: a practical guide for clinicians." Nutr Clin Pract. 2007 Aug;22(4):377-88.
- ^ a b Pinheiro Volp AC, et al. "Energy expenditure: components and evaluation methods." Nutr Hosp. 2011 May-Jun;26(3):430-40. doi: 10.1590/S0212-16112011000300002.
- S2CID 23682662. citing Nishi, Y. (1981). "Measurement of thermal balance in man". In K. Cena & J. Clark (ed.). Bioengineering, Thermal Physiology and Comfort. Elsevier. pp. 29–39.
- ^ Atwater WO, et al. "Description of neo respiration calorimeter and experiments on the conservation of energy in the human body." US Department Agriculture, Off Exp Sta Bull 63, 1899
- ^ a b McClave SA, et al. "Use of indirect calorimetry in clinical nutrition." Nutr Clin Pract. 1992 Oct;7(5):207-21.
- ^ Douglas, C. Gordon (18 March 1911). "A method for determining the total respiratory exchange in man". Proceedings of the Physiological Society. Retrieved 28 August 2016.[dead link] (Douglas Bag)
- ^ Academy of Nutrition and Dietetics "Measuring RMR with Indirect Calorimetry (IC)." Nutr Clin Pract. 2007 Aug;22(4):377-88.