Monitoring of cerebrovascular pressure reactivity (PRx) has diagnostic and prognostic value in head-injured patients, but requires invasive monitoring of intracranial pressure (ICP). Near infrared spectroscopy (NIRS) is a noninvasive method that is suitable for continuous detection of cerebral blood volume changes. We compared a NIRS-based index of cerebrovascular reactivity, called total
hemoglobin reactivity (THx), against standard measurements of PRx in a prospective observational study. Forty patients with
closed-head injury were monitored daily with arterial blood pressure (ABP), ICP, and a NIRS-based total
hemoglobin index. PRx and THx were calculated as the moving correlation coefficients using 5-min time windows between 10-sec averaged values of ICP and ABP, and total
hemoglobin index and ABP, respectively. A total of 120 recordings were performed between the median first (IQR 0.75-2) and fourth (IQR 2-6) day after
head injury, giving a total duration of 1760 hours. PRx and THx demonstrated a significant association across averaged individual recordings (r = 0.49, p < 0.0001), and across patients (r = 0.56, p = 0.0002). Assessment of optimal cerebral perfusion pressure (
CPP) and ABP using THx was possible in about 50% of recordings, and showed a significant agreement with the optimal
CPP and ABP assessed with PRx. THx may be of diagnostic value to optimize
therapy oriented toward restoration and continuity of cerebrovascular reactivity, especially in patients for whom direct ICP monitoring is not feasible.