One-minute dynamic cerebral autoregulation in severe head injury patients and its comparison with static autoregulation. A transcranial Doppler study.

OBJECTIVE: To compare dynamic and static responses of cerebral blood flow to sudden or slow changes in arterial pressure in severe traumatic brain injury (TBI) patients.
DESIGN: Prospective study. PATIENTS AND METHODS: We studied 12 severe TBI patients, age 16-63 years, and median GCS 6. We determined the dynamic cerebral autoregulation: response of cerebral blood flow velocity to a step blood pressure drop, and the static cerebral autoregulation: change in cerebral blood flow velocity after a slow hypertensive challenge.
RESULTS: During the dynamic response, the median drop in arterial pressure was 21 mm Hg. Dynamic response was graded between 9 (best) and 0 (worst). The median value was 5; four patients showed high values, (8-9), five patients showed intermediate values (4-6). In three patients (value = 0), the CBFV drop was greater than the cerebral perfusion pressure drop, and maintained through 60 s. The static cerebral autoregulation was preserved in 6/11 patients. The comparison between the two showed four different combinations. The five patients with impaired static cerebral autoregulation showed unfavorable outcome.
CONCLUSIONS: A sharp dynamic vasodilator response could not be sustained, and a slow or absent reaction to a sudden hypotensive challenge could show an acceptable cerebral autoregulation in the steady state. We found that patients with impaired static cerebral autoregulation had a poor outcome, whereas those with preserved static cerebral autoregulation experience favorable outcomes.