Variation in the resting metabolic rate of mechanically ventilated critically ill patients

There has been increasing interest in the nutritional support of the critically ill patient. The day-to-day variation in resting energy expenditure (REE) was studied over a 3-5-day period in 17 postoperative mechanically ventilated critically ill patients to gain insight as to how often caloric intake should be reassessed, whether changes observed over 3-5 days are of sufficient magnitude to make frequent adjustments in caloric intake, and what factors are associated with large alterations in metabolic rate. REE was measured daily for 3-5 days, and the percent variation in REE [(highest REE--lowest daily REE)/(lowest daily REE) x 100] calculated. The variation ranged from 4 to 56%, and on further analysis two distinct groups were identified, one with a mean variation of 12 +/- 4% (SD) (range 4-18%) and the other with a mean variation of 46 +/- 8% (range 37-56%). The former group was clinically stable, whereas the latter was not. Clinically stable patients need less frequent measurements than those who are more ill, but when designing a nutritional regimen for them, at least 20-25% should be added to the REE, 15% to account for day-to-day variation and 5-10% for activity.