Comparison of Pressure Reactivity Index and Mean Velocity Index to Evaluate Cerebrovascular Reactivity During Induced Arterial Blood Pressure Variations in Severe Brain Injury.

Objectives: To compare the assessment of cerebral autoregulation by cerebrovascular reactivity indices based on intracranial pressure (Pressure Reactivity Index, PRx) and on transcranial Doppler (Mean Velocity Index, Mx) during controlled variations of arterial blood pressure in severe brain injury. Primary outcome was the agreement between both cerebrovascular reactivity indices measured by the Bland-and-Altman method. Secondary outcomes were the association of cerebrovascular reactivity indices with arterial blood pressure variation, and the comparison of optimal cerebral perfusion pressures determined by both indices.

Methods: All consecutive comatose (Glasgow Coma Scale < 8) patients from the surgical intensive care unit of Bicetre Hospital who had an acute brain injury on computerized tomography and needed vasopressor support were prospectively included. Step-by-step arterial pressure variations using vasopressors were performed to compare PRx and Mx and to calculate optimal cerebral perfusion pressure (CPPopt).

Measurements And Main Results: 15 patients were included. Mean difference between both indices measured by Bland-and-Altman plot was - 0.07 (IC 95% [- 1.02 to 0.87]). Mx was significantly associated with arterial pressure variation (one-way ANOVA test, p = 0.007), whereas PRx was not (p = 0.44). Optimal cerebral perfusion pressure calculated with PRx and Mx was respectively 11 and 15mmHg higher than the mean perfusion pressure prescribed. Optimal cerebral perfusion pressure calculation was possible in all cases.

Conclusions: Cerebral vasoreactivity indices calculated with intracranial pressure or transcranial Doppler show only moderate agreement. Both indices nonetheless suggest substantially higher optimal cerebral perfusion pressure than those currently provided by international guidelines.