Ahead of Print: PI for ICP/CPP Assessment
Background: It has been postulated that Gosling’s pulsatility-index (PI) assessed with transcranial Doppler (TCD) has a diagnostic value for non-invasive estimation of intracranial pressure (ICP) and cerebral perfusion pressure (CPP).
Objective: To revisit this hypothesis using a database of digitally stored signals from a cohort of head injured patients.
Methods: We analyzed prospectively collected data of patients admitted to the Cambridge Neuroscience critical care unit who had continuous recordings of ABP, ICP, and cerebral blood flow velocities (FV) using TCD. PI was calculated (Fvsys-Fvdia/Fvmean) over each recording session. Statistical analysis was performed using Spearman’s rank correlation, Receiver-Operator-Characteristics (ROC) methods, and modeling of a non-linear PI-ICP/CPP graph.
Results: 762 recorded daily sessions from 290 patients were analyzed with a total recording time of 499.9 hours. The correlation between PI and ICP was 0.31 (p<0.0001) and for PI and CPP -0.41 (p<0.0001). The 95% prediction interval of ICP values for a given PI was more than +/-15 mmHg and for CPP more than +/-25 mmHg. The diagnostic value of PI to assess ICP area-under-curve (AUC) ranged from 0.62 (ICP>15mmHg) to 0.74 (ICP>35mmHg). For CPP, the AUC ranged from 0.68 (CPP<70mmHg) to 0.81 (CPP<50mmHg). Probability charts for elevated ICP/ lowered CPP depending on PI were created.
Conclusion: Overall, the value of TCD-PI to assess non-invasively ICP and CPP is very limited. However, extreme values of PI can still potentially be used in support of a decision for invasive ICP monitoring.
From: Reliability of the Blood Flow Velocity Pulsatility Index for Assessment of Intracranial and Cerebral Perfusion Pressures in Head Injured Patients by Zweifel et al.