Spontaneous cerebral hypothermia after severe head injury: Relation with brain chemistry and cerebrovascular parameters

Secondary ischemic events are one of the major causes of bad outcome in patients with severe traumatic brain injury (TBI). Multiple clinical trials testing diverse neuroprotective compounds have so far failed to provide new therapies. Nevertheless, multiple studies using hypothermia have shown evidence of benefit, and the latest results of a U.S. multicenter hypothermia trial are awaited. Meanwhile hypothermia is being used in many neurosurgical centers all over the world and especially in Japan. We therefore retrospectively analyzed patients suffering from TBI with a Glascow Coma Scale (GCS) score of 8 or less. We studied brain temperature using a multiparameter sensor, brain chemistry using microdialysis, intracranial pressure (ICP) using a ventriculostomy, and cerebral blood flow (CBF) using stable-xenon CT. Patients were retrospectively separated into four temperature cohorts according to their brain temperature. Patients with spontaneous hypothermia (Tbr < 36 degrees C) significantly differed from the other cohorts. The mean ICP (P < 0.01), cerebral perfusion pressure (CPP) (P < 0.001), and glutamate P < 0.0004) were significantly higher, whereas the CBF (P < 0.05) and brain glucose were lower. A negative brain temperature-rectal temperature (Trect) difference (Delta Tbr-Trect) was correlated with a bad outcome as observed in the patients with spontaneous brain hypothermia and those with therapeutic cooling. When monitoring severely brain-injured patients, spontaneous brain hypothermia and a negative brain to rectal temperature difference (Delta Tbr-Trect) represents an indicator of bad outcome and brain chemistry derangement (glutamate, lactate, glucose) and CBF.