Cerebrovascular reactivity during hypothermia and rewarming

Background. Experimental evidence from a murine model of traumatic brain injury (TBI) suggests that hypothermia followed by fast rewarming may damage cerebral microcirculation. The effects of hypothermia and subsequent rewarming on cerebral vasoreactivity in human TBI are unknown. Methods. This is a retrospective analysis of data acquired during a prospective, observational neuromonitoring and imaging data collection project. Brain temperature, intracranial pressure (ICP), and cerebrovascular pressure reactivity index (PRx) were continuously monitored. Results. Twenty-four TBI patients with refractory intracranial hypertension were cooled from 36.0 (0.9) to 34.2 (0.5)8C [mean (SD), P,0.0001] in 3.9 (3.7) h. Induction of hypothermia [average duration 40 (45) h] significantly reduced ICP from 23.1 (3.6) to 18.3 (4.8) mm Hg (P,0.05). Hypothermia did not impair cerebral vasoreactivity as average PRx changed non-sig-nificantly from 0.00 (0.21) to 20.01 (0.21). Slow rewarming up to 37.08C [rate of rewarming, 0.2 (0.2)8C h21] did not increase ICP [18.6 (6.2) mm Hg] or PRx [0.06 (0.18)]. However, in 17 (70.1%) out of 24 patients, rewarming exceeded the brain temperature threshold of 378C. In these patients, the average brain temperature was allowed to increase to 37.8 (0.3)8