Which of the following statement(s) is/are true concerning the estimation and measurement of energy requirements in the critically ill patient?

b. The amount of oxygen absorbed through the lungs is equal to the amount of oxygen consumed by metabolic processes

c. Metabolic rate, normalized to body surface area, may underestimate metabolism in a fat person

The actual metabolic rate of any patient can be estimated from the predicted basal rate according to the clinical situation. The amount of energy is most conveniently expressed in calories/day. The metabolic rate is normalized to body surface area; however, the actively metabolizing tissue is the lean body cell mass. Consequently, reporting “per square meter” underestimates metabolism in a fat person and overestimates in a very lean person. Although most of studies on nutrition in critical illness have been based on estimated energy expenditure, actual measurement is much more accurate and has become an important aspect of critical care management. The most commonly used method of measurement is indirect calorimetry. In this method, the amount of oxygen absorbed across the lungs into the pulmonary blood is measured over a given period of time. Assuming the patient is at a metabolic steady state during this time, the amount of oxygen absorbed across the lungs is equal to the amount of oxygen consumed in the metabolic process. The metabolic rate, measured in cubic centimeters of oxygen/minute, can be converted to calories/hour or /day if the oxygenated substrates are known. For practical purposes, a conversion factor of 5 kcal of energy/liter of oxygen consumed is a reasonable approximation.