Joseph Orr, Ph.D.

University of Utah, Department of Anesthesiology

Salt Lake City, Utah, USA 84132

Introduction:

Resting metabolic rate (RMR) is the rate at which a person burns calories while at rest. Between 70 and 80% of all calories are burned under resting conditions. Knowledge of metabolic rate is vital to nutritional assessment, weight loss planning and care of various medical conditions.

The primary method of metabolic rate measurement is indirect calorimetry. In indirect calorimetry, the rate at which oxygen is consumed and carbon dioxide is produced are measured directly and the caloric burn rate is calculated from the measured oxygen consumption and CO2 production. The relationship between oxygen consumed and calories burned is defined by the Wier equation [1,2]. The standard Wier equation defines the relationship between oxygen consumption (VO2), CO2 production and energy expenditure. Weir also showed that for a specific measurement technique, energy expenditure (caloric burn rate) could be measured without requiring carbon dioxide production measurements [1,2].

Testing of an indirect calorimeter based on Weir’s “O2 only” method is described here. The test system (ReeVue, Korr Medical Technologies, Salt Lake City, UT) is less complex and much less expensive than the standard metabolic rate measurement instruments. Traditionally, metabolic measurements are large instruments that require frequent calibration of their oxygen and CO2 sensors. This type of system is often referred to as a “metabolic cart” because the size of the instrument and related computer and calibration equipment required a cart for transport within the hospital. We compared the REEVUE system against the Deltatrac metabolic cart (Datex-Ohmeda, Finland). The Deltatrac system represents an established clinical standard that has been validated clinically and in-vitro [3,4].