Metabolic Rate in Older Critically Ill Patient
Age is a known factor in determining resting metabolic rate in healthy people. Resting metabolic rate falls as age increases. The decrease seems to be associated with an age-dependent decrease in fat-free mass rather than a decrease in metabolic rate per unit of mass. This decrease in resting metabolic rate is captured in many predictive equations, which have a variable for age. A surprisingly limited amount of data exists on the resting metabolic rate of elderly critically ill patients. In one small study of trauma patients, the resting metabolic rate was reduced in older patients compared to younger, but the decrease was proportional to the expected decrease in resting metabolic rate in healthy aging. The incidence of fever was also lower in the older patients. In a much larger sample of trauma, surgical, and medical critical care patients prepared for this chapter, a lower body temperature and resting metabolic rate were again noted. The resting metabolic rate difference remained even after controlling for age, body size, and body temperature. Resting metabolic rate in the critically ill patient is predicted almost as well in the elderly as in the young.
KeywordsMetabolic Rate Minute Ventilation Healthy Aging Indirect Calorimetry Predictive Equation
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