Energy expenditure, nitrogen balance, and norepinephrine excretion after injury

In this study we examine the effect of different hypocaloric nutritional regimens on nitrogen balance in patients following total hip replacement and compare it to that of normal subjects on strict bed rest. The interrelationship between nitrogen balance, energy expenditure, and urinary free norepinephrine excretion is analyzed with emphasis on the effects of nutrition on these relationships. Amino acid infusions following major elective orthopedic surgery had no nitrogen-sparing effect above that of 5% dextrose. Optimum nitrogen balance was obtained by administration of both 5% dextose and 3.5% amino acids. Patients receiving 5% dextrose showed no increase in resting energy expenditure in postoperative period compared to the preoperative control value. However, patients receiving amino acid infusions showed a 14% rise in energy expenditure postoperatively. Failure to administer 5% dextrose was associated with a high urinary norepinephrine excretion postoperatively. In normal subjects on bed rest either 5% dextrose or total starvation resulted in a marked fall in resting energy expenditure, whereas amino acid infusions isocaloric to the carbohydrate intake prevented any fall in resting energy expenditure. Nitrogen balance was improved with amino acid infusions in normal subjects. This study suggests the effect of amino acid infusions is highly dependent on the metabolic state of the patient.