Intravenous glutamine supplementation to head trauma patients leaves cerebral glutamate concentration unaffected

Objective: There is reluctance to use glutamine-containing i. v. nutrition for neurosurgical patients, as this may result in elevated intracerebral glutamate levels, which are thought to be associated with neuronal injury and cell swelling, causing an increase in ICP and an unfavourable outcome. As general ICU patients benefit from i. v. glutamine supplementation in terms of reduced mortality and morbidity, neurosurgical patients might also be candidates for such treatment, if the possible relation between i. v. glutamine supplementation and a possible increase in cerebral glutamate could be sorted out. Design and setting: The study protocol had a crossover design with a 24 h treatment period and a 24 h placebo period in random order. Treatment was a glutamine containing dipeptide, L-alanyl-L-glutamine 200 mg/ml, for 20 h; placebo was saline. The rate of infusion was 0.125 ml/kg/h, which is equal to 0.34 g/kg of glutamine over the 20 h period. Microdialysate was collected for analysis in 120 min portions. The flow through the microdialysis catheter was 0.3 mu l/min. Subjects: Patients with severe head trauma (GCS <= 8; n = 15) on routine monitoring, including intracerebral microdialysis, were randomly assigned to treatment followed by placebo or placebo followed by treatment. Measurements and results: Glutamine infusion increased plasma glutamine concentration by 30%, but not plasma glutamate concentration. Intracerebral glutamate was unaffected in median values and in all individual patients. Conclusion: Intravenous glutamine in clinically relevant doses leaves cerebral glutamate unaffected. This opens the possibility of evaluating the effects of i. v. glutamine supplementation upon outcome for neurosurgical ICU patients.