Continuous Assessment of the Cerebral Vasomotor Reactivity in Head Injury

TLDR

Cerebrovascular vasomotor reactivity reflects arterial smooth‑muscle tone changes in response to pressure or CO₂ variations. The study examined whether slow waves in arterial blood pressure and intracranial pressure could yield an index of vascular reactivity to arterial pressure changes. In 82 head‑injury patients, ABP, ICP, and middle cerebral artery flow velocity were recorded daily, and a Pressure‑Reactivity Index (PRx) was computed as a moving correlation of 40 consecutive 5‑second samples, alongside a Mean Index correlation between flow velocity and cerebral perfusion pressure. Positive PRx correlated with higher ICP, lower admission GCS, and worse 6‑month outcomes, was significant only in patients with unfavorable outcomes during the first two days, and showed a strong correlation with the Mean Index (r = 0.63), indicating that continuous analysis of slow ABP and ICP waves provides a prognostically valuable cerebrovascular reactivity index.

Abstract

OBJECTIVE: Cerebrovascular vasomotor reactivity reflects changes in smooth muscle tone in the arterial wall in response to changes in transmural pressure or the concentration of carbon dioxide in blood. We investigated whether slow waves in arterial blood pressure (ABP) and intracranial pressure (ICP) may be used to derive an index that reflects the reactivity of vessels to changes in ABP. METHODS: A method for the continuous monitoring of the association between slow spontaneous waves in ICP and arterial pressure was adopted in a group of 82 patients with head injuries. ABP, ICP, and transcranial doppler blood flow velocity in the middle cerebral artery was recorded daily (20- to 120-min time periods). A Pressure-Reactivity Index (PRx) was calculated as a moving correlation coefficient between 40 consecutive samples of values for ICP and ABP averaged for a period of 5 seconds. A moving correlation coefficient(Mean Index) between spontaneous fluctuations of mean flow velocity and cerebral perfusion pressure, which was previously reported to describe cerebral blood flow autoregulation, was also calculated. RESULTS: A positive PRx correlated with high ICP (r = 0.366;P < 0.001), low admission Glasgow Coma Scale score (r = 0.29; P < 0.01), and poor outcome at 6 months after injury(r = 0.48; P < 0.00001). During the first 2 days after injury, PRx was positive (P < 0.05), although only in patients with unfavorable outcomes. The correlation between PRx and Mean Index(r = 0.63) was highly significant (P < 0.000001). CONCLUSION: Computer analysis of slow waves in ABP and ICP is able to provide a continuous index of cerebrovascular reactivity to changes in arterial pressure, which is of prognostic significance.