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.