Object. The goal of this study was to elucidate the optimal time for rewarming of patients who have been treated with hypothermia for severe head injury.
Methods. Eleven patients with severe head injuries who had been treated by hypothermia underwent transcranial Doppler (TCD) ultrasonography examinations. The patients were divided into two groups: Group A consisted of three patients in whom acute brain swelling occurred during the rewarming period and Group B was composed of eight patients who displayed no significant intracranial hypertension during or after hypothermia therapy. In all patients, the mean flow velocity of the middle cerebral artery (FVMCA) recorded transcranially and the mean flow velocity of the internal carotid artery (FVICA), recorded high in the neck, were monitored at 24-hour intervals after the patient was admitted to the hospital. In Group A, the FVMCA was normal at 48 hours (maintenance state of hypothermia) in each patient, and abnormal increases and peak values (> 100 cm/second) occurred from 96 to 144 hours postinjury (rewarming period). The FVICA, which was monitored concurrently also varied as the FVMCA increased. The pulsatility indices in the arteries decreased at the time of the peak FVMCA. The enhanced FVMCA was consistent with hyperemia because of the low FVMCA/FVICA ratios (< 3). Two patients in whom jugular venous oxygen saturation was monitored were found to have high values (> 80%), representing hyperemia. All intracranial pressures (ICPs) that lay within the normal range at 48 hours postinjury elevated acutely after the peak FVMCA. In Group B, both FVMCA and FVICA values were normal at 48 hours postinjury and remained stable throughout the rewarming period. Values of ICP were also maintained within the normal range until the patients were weaned from hypothermia therapy.
Conclusions. Hyperemia, detectable by TCD ultrasonography, may serve as an index in the prediction of acute brain swelling, and rewarming should be terminated when such a hemodynamic phenomenon is observed.