The pattern of amino acid exchange across the brain is unaffected by intravenous glutamine supplementation in head trauma patients.

BACKGROUND & AIMS: Exogenous intravenous glutamine supplementation to head trauma patients leaves intracerebral glutamate concentration unaffected. The effect of an exogenous supply upon glutamine and glutamate exchange across the brain has still not been characterised.

METHODS

A prospective randomised cross-over study, where i.v. glutamine dipeptide was compared with placebo. Arterio-venous concentration differences of free amino acids across the brain and amino acid flux across the leg were measured. In addition, the endogenous glutamine production was calculated. Fifteen mechanically ventilated head trauma patients with GCS < or =8 were included and studied during two consecutive 24-h periods on days 2-5 following head trauma.

RESULTS

Glutamine was continuously released from both the brain and the leg. The arterio-venous (a-v) concentration differences over the brain were calculated to be -49+/-26 and -27+/-14 micromol/L during the treatment and control periods respectively, showing a continuous release of glutamine (p<0.0001). On the other hand, the a-v difference of glutamate was not different from zero (p>0.2). The whole-body glutamine rate of appearance (R(a)) was calculated to be 218+/-75micromol/kg body weight/h.

CONCLUSION

Intravenous glutamine supplementation to head trauma patients was associated with an unaffected amino acid exchange pattern across head and leg, without any measurable uptake of glutamate across the brain. Endogenous glutamine production was in the normal range despite the low plasma glutamine concentration. This pilot study opens the possibility to perform prospective clinical trials in head trauma patients to evaluate the clinical efficacy of exogenous glutamine supplementation.