Metabolic Response to Injury and Illness: Estimation of Energy and Protein Needs from Indirect Calorimetry and Nitrogen Balance

TLDR

Injury and illness trigger increased energy expenditure and nitrogen losses, complicating the assessment of calorie and protein requirements. The study proposes a method to determine daily calorie needs for hospitalized patients. Resting metabolic rates were measured by indirect calorimetry across diverse clinical conditions, and total calorie needs were calculated using the Harris‑Benedict equation adjusted for activity and injury, while protein requirements were estimated from 24‑hour urinary nitrogen excretion. This approach more accurately reflects patients’ variable calorie and protein needs during peak catabolism and recovery.

Abstract

The metabolic response to injury and illness as manifested by increases in energy expenditure and nitrogen losses makes it difficult for the clinician to evaluate calorie and protein needs. A method for determining daily calorie needs in hospitalized patients is presented. Average increases in resting metabolic expenditure for a group of patients following elective operation, skeletal trauma, skeletal trauma with head injury, blunt trauma, sepsis and burns were determined by indirect calorimetry and protein need by urinary nitrogen losses over extended time periods. Total daily calorie needs were then calculated, using the Harris-Benedict equation and adjusting this value upward using a previously measured activity and injury factor to arrive at the daily needs. Protein requirements may be determined on periodic 24 hour urine samples analyzed for the urinary urea nitrogen and adjusting this to a total nitrogen or protein equivalent. This approach to estimating the calorie nitrogen needs of the hospitalized patient under various degrees of stress more closely approximates the patient's variable needs at the height of the catabolic response and during convalescence.