Nutritional and metabolic variables correlate with amino acid forearm flux in patients with severe head injury

Abstract

To measure the arterial-venous amino acid flux across the forearm muscle in patients with severe head injury.Prospective, interventional study.Level I trauma hospital in the neurosurgery intensive care unit (ICU) at a university medical center.Eight nonsteroid-treated patients with severe head injury.Patients were prospectively randomized to receive either standard or supplemental intravenous zinc therapy.Net forearm alanine, glutamine, tyrosine, phenylalanine, and branch-chain amino acid forearm flux were measured and compared with metabolic markers of energy expenditure and nitrogen excretion. There was a significant inverse relationship between the measured energy expenditure/predicted energy expenditure ratio and glutamine flux (r2 = .62; p < .05). The patients with the highest measured energy expenditure/predicted energy expenditure ratio had the greatest release of glutamine from forearm muscle. Nitrogen balance was significantly correlated with leucine flux (r2 = .53; p < .05) and with isoleucine flux (r2 = .67; p < .05). The patients with the most positive nitrogen balance had the least release of branch-chain amino acids from skeletal muscle. Tyrosine flux was highly correlated with net amino acid flux (r2 = .76; p < .01). Tyrosine flux was therefore indicative of overall muscle catabolism. Four patients had an overall negative flux of amino acids from skeletal muscle. Three patients had an overall negative flux of branch-chain amino acids.This preliminary descriptive report suggests that increased skeletal muscle efflux of amino acids correlates significantly with metabolic variables of hypermetabolism and hypercatabolism in nonsteroid-treated, head-injured patients.