Evolution of energy expenditure and nitrogen excretion in severe head-injured patients

The aim of the study was to estimate the influence of therapeutic changes on the level of energy expenditure (EE) and N excretion in a homogeneous group of patients usually considered hypermetabolic.

EE and N excretion of head-injured patients were measured simultaneously at phases 1 and 2 (patients treated 4 +/- 3 and 18 +/- 8 days after injury, respectively).

Acute care hospital.

Eight severe head-injured patients, mean weight 63.1 +/- 6.1 (SD) kg, mean age 21 +/- 3.8 (SD) yr.

At phase 1, all patients were sedated with fentanyl (6.7 +/- 1.9 micrograms/kg.hr) plus flunitrazepam (9.1 +/- 4.8 micrograms/kg.hr) and were mechanically ventilated. All patients received continuous total parenteral nutrition. The nonprotein caloric intake averaged 1092 +/- 200 kcal/day, including 77% glucose and 23% fat (Intralipid 20%). The total N intake averaged 7 +/- 5 g/day, consisting of crystalline amino acids. At phase 2, no patient received any sedative and all were breathing spontaneously via tracheostomy. All patients received parenteral and/or enteral nutrition. The nonprotein caloric intake averaged 1929 +/- 200 kcal/day consisting of 65% carbohydrates and 35% fat. The total N intake averaged 13 +/- 2 g/day.

The EE was significantly higher at phase 2 than at phase 1 (2121 vs. 1737 kcal), but the interindividual variability was low at both phases. N excretion was high at the two periods of the study and not correlated to the level of EE. The RQ was 0.75 at both periods, indicating predominant fat oxidation.

We could not demonstrate any parallelism in the evolution of EE and protein catabolism in head-injured patients. The therapeutics (mechanical ventilation, sedation, and nutrition) have a major effect on EE but little on N excretion.