Monitoring of the association between cerebral blood flow velocity and intracranial pressure

Slow waves in intracranial pressure (ICP) are believed to originate from changes in cerebral blood volume secondary to adjustments in arteriolar diameter. Blood flow velocity (FV) signals recorded with transcranial Doppler ultrasound show similar oscillations. We investigated a continuous measure of FV/ICP association and its relationship to cerebral perfusion pressure (CPP), ICP, cerebral autoregulation (CA) and outcome after severe traumatic brain injury (TBI). We analysed recordings of arterial blood pressure (ABP), FV and ICP from 187 TBI patients treated at Addenbrooke's Hospital, Cambridge, UK, from 1993 to 1998. Monitored data were recorded and the flow-ICP index (Flx) was derived as a moving correlation between the two signals over 4-min periods using ICM+. FIx was compared with the autoregulatory index (Mx), pressure reactivity index (PRx), ICP, CPP and outcome. FIx correlated with ICP (Spearman's R =-0.40, p < 0.01), Mx (R =-0.54, p < 0.00005) and CPP (R = 0.34, p < 0.01), but not with PRx (p = 0.84). FIx was significantly associated with outcome after grouping into Glasgow Outcome Score (GOS) 1-3 or GOS 4-5 (Mann-Whitney p = 0.009). FIx may provide unique insights into the behaviour of the cerebral circulation during intracranial hypertension.