Clinical significance of cerebral autoregulation.
OBJECTIVE
Disturbed cerebral autoregulation is believed to be associated with an unfavourable outcome following head injury. Previously, using ICP monitoring and transcranial Doppler ultrasonography, we investigated whether cerebral response to spontaneous variations in arterial pressure (ABP) or cerebral perfusion pressure (CPP) provide reliable information on cerebral autoregulatory reserve. In the present study we have correlated these methods with clinical findings.


METHODS
188 head injured sedated and ventilated patients were studied daily. Waveforms of intracranial pressure (ICP), arterial pressure and transcranial Doppler flow velocity (FV) were captured over a half to two hour periods. Time averaged mean flow velocity (FV) and CPP were resolved. The correlation coefficient indices between FV and CPP (Mx) and between ICP and ABP (PRx) were calculated over 3 minutes epochs, and averaged for each investigation.


RESULTS
The relationship between indices of autoregulation and outcome (favourable-unfavourable) was significant and stronger than the association between admission GCS and outcome. With rigorously maintained CPP-oriented therapy relationship between CPP and outcome became non-significant. Mortality in patients with consistently disturbed autoregulation ranged 47%, while in patients with good autoregulation mortality was 11% (difference: p < 0.0001).


CONCLUSIONS
Positive values of indices of autoregulation, expressing positive association between slow waves of CPP and blood flow velocity or ABP and ICP, indicate disturbed autoregulation. These indices correlate with unfavourable outcome following head injury and should be used to guide intensive therapy.
Czosnyka
M
M
Academic Neurosurgical Unit, Addenbrooke's Hospital, Cambridge, UK.
Smielewski
P
P
Piechnik
S
S
Pickard
J D
JD
D001783:Blood Flow Velocity; D006259:Craniocerebral Trauma / Q000000981:diagnostic imaging / Q000401:mortality / Q000503:physiopathology* / Q000628:therapy*; D006706:Homeostasis; D006801:Humans; D007427:Intracranial Pressure / Q000502:physiology*; D008991:Monitoring, Physiologic / Q000379:methods; D012044:Regression Analysis; D012121:Respiration, Artificial; D016019:Survival Analysis; D016896:Treatment Outcome; D017585:Ultrasonography, Doppler, Transcranial