Cerebrovascular Pressure Reactivity Monitoring Using Wavelet Analysis in Traumatic Brain Injury Patients: A Retrospective Study

Background After traumatic brain injury (TBI), the ability of cerebral vessels to appropriately react to changes in arterial blood pressure (pressure reactivity) is impaired, leaving patients vulnerable to cerebral hypo- or hyper-perfusion. Although, the traditional pressure reactivity index (PRx) has demonstrated that impaired pressure reactivity associates with poor patient outcome, PRx is sometimes erratic and may not be reliable in various clinical circumstances. Here, we introduce a more robust wavelet transform based pressure reactivity index (wPRx) and compare its performance with the widely used traditional PRx across three areas: its stability and reliability in time, its ability to give an optimal cerebral perfusion pressure (CPPopt) recommendation and its relationship with patient outcome. Methods and Findings 515 TBI patients admitted in Addenbrooke’s Hospital, UK (March 23rd, 2003- December 9th, 2014), with continuous monitoring of arterial blood pressure (ABP) and intracranial pressure (ICP) were retrospectively analyzed to calculate the traditional PRx and a novel wavelet transform based wPRx. wPRx was calculated by taking the cosine of the wavelet transform phase-shift between ABP and ICP. A time trend of CPPopt was calculated using an automated curve fitting method that determined the CPP at which the pressure reactivity (PRx or wPRx) was most efficient (CPPopt_PRx and CPPopt_wPRx, respectively). There was a significantly positive relationship between PRx and wPRx (r = 0.73) and wavelet wPRx was more reliable in time (ratio of between-hour variance to total variance, wPRx 0.957± 0.0032 vs PRx and 0.949 ± 0.047 for PRx, p=0.002). The 2-hour interval standard deviation of wPRx (0.19± 0.07) was smaller than that of PRx (0.30 ± 0.13, p<0.001). wPRx performed better in distinguishing between mortality and survival (AUROC for wPRx was 0.73 vs 0.66 for PRx, p = 0.003). The mean difference between the patients’ CPP and their CPPopt was related to outcome for both calculation methods. There was a good relationship between the two CPPopts (r=0.814, p<0.001). CPPopt_wPRx was more stable than CPPopt_PRx (within patient standard deviation 7.05 ± 3.78 vs 8.45 ± 2.90; p