Ketamine and Glutamate After Brain Injury : a Microdialysis Study

Inclusion of 20 consecutive head trauma patients. Randomization and double-blind to compare the effects of ketamine versus sufentanil on brain glutamate concentrations measured with microdialysis.

Ketamine is an anti-N-methyl-D-aspartate (NMDA) medication. It is supposed to limit excitotoxicity of amino-acids, especially glutamate. Glutamate is known to be elevated in more than 60% of the severe head trauma patients. It induces cortical spreading depression which can aggravate prognosis. It's a daily used medication in anesthesia and intensive care units for sedation and induction of anesthesia. It's the recommended medication for induction of unstable wounded soldiers on the field because of its neutrality on haemodynamic state.

Sufentanil is the reference opioid for sedation in ICU in Europe. It can induce hypotension which is deleterious for cerebral perfusion pressure after brain trauma.

In our unit, patients with severe head injury are monitored by a triple lumen access device including ICP (IntraCerebral Pressure), PtiO2 (oxygen pressure in the brain) and microdialysis. This last monitoring allows measurement of brain parenchymal concentrations of small molecules : glucose, lactate, pyruvate, glutamate, glycerol,.... It's a tool to evaluate the metabolic state of the brain divided into 4 categories : normal, hyperglycolysis, ischemia and metabolic crisis.

Then, we will detail the effects of ketamine on metabolic state of the brain, especially glutamate concentration. Normal values are below 10 micromol/ml. After head trauma it can dramatically increase to values up to 50 or even 100 micromol/ml, with normalization after 24 hours. Ketamine is expected to decrease these high values faster than described in observational studies.