Background: Transcranial Doppler (TCD) is a noninvasive bedside tool for intracerebral hemodynamic assessments in multiple clinical scenarios. TCD, by means of measuring systolic and diastolic blood velocities allows the calculation of the pulsatility index (PI), a parameter that is correlated with intracranial pressure (ICP). Nevertheless, the predictive value of the PI for raised ICP appears to be low, since it is subjected to several, often confounding factors not related to ICP. Recently, the Pulsatile Apparent Resistance (PaR) was developed as a PI corrected for arterial blood pressure, reducing some of the confounding factors in uencing PI. This study compares the predictive value of PaR versus PI for intracranial hypertension (IH, ICP >20 mmHg) in patients with traumatic brain injury (TBI).Methods: Patients with TBI admitted to the neurocritical care unit who required invasive ICP were included prospectively within ve days of admission. TCD measurements were performed in both middle cerebral arteries, allowing calculations of the PI and PaR. The discriminative power of these parameters for ICP ≥20 mmHg was assessed by calculating the area under the Receiver Operator Characteristics curve (AUC).Results: 93 patients were included. A total of 20 (22%) patients experienced IH. The discriminative power was low for PI (AUC 0.64, 95% Con dence Interval (CI) 0.49 -0.79) and moderate for PaR (AUC 0.75, 95% CI 0.63 -0.86). With regard to subgroup analyses, the discriminative power of these parameters increased after exclusion of patients who had undergone a craniectomy. This was especially true for the PaR (AUC right side 0.88; CI 0,72 -1,0) and PI (AUC right side 0.72; CI 0,44 -1,0).
Conclusion:In the present study, discriminative power of the PaR for IH was superior to the PI, especially in patients not having undergone craniectomy. The assessment of PaR may be an adjunct especially for improving timing on a neurosurgical intervention, but also for their monitoring after a neurosurgery is performed. Further studies are warranted to de ne its clinical application. Trial registration: NCT03144219, Registered 01 May 2017 Retrospectively registered, https://www.clinicaltrials.gov/ct2/show/NCT03144219 Take Home Message 1. The transcranial Doppler (TCD) pulsatility index (PI), although being useful to indicate elevation in cerebrovascular resistance, suffers with the in uence of several factors that make this index less accurate in indicating intracranial hypertension (IH).2. The pulsatile apparent resistance (PaR) index was developed to adjust the PI for arterial blood pressure pulsatility, increasing its accuracy compared to the PI.3. The PaR value had a better discriminative power than the PI with regards to IH, with a moderate area under the curve (AUC) for the whole sample, but with a good AUC after exclusion of patients who had undergone craniectomy.
