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In patients with subarachnoid hemorrhage, the assessment of cerebral autoregulation aids in prognosis as well as detection of vasospasm. Mx is a validated index of cerebral autoregulation based on measures of cerebral perfusion pressure and mean flow velocity on transcranial Doppler but is impractical for longer-term monitoring. Near-infrared spectroscopy is noninvasive and suitable for continuous monitoring of cerebral tissue oxygenation using the Tissue Oxygenation Index. In this study, we compared near-infrared spectroscopy-based indices of cerebral autoregulation (TOx) with Mx in patients with subarachnoid hemorrhage.Arterial blood pressure, intracranial pressure, mean flow velocity, and Tissue Oxygenation Index were recorded. Mx and TOx were calculated as moving correlation coefficients between 10-second averaged values of cerebral perfusion pressure and mean flow velocity and between cerebral perfusion pressure and Tissue Oxygenation Index. We also calculated TOxA, the moving correlation coefficient between arterial blood pressure and Tissue Oxygenation Index.Fifty-one recording sessions were performed in 27 patients with subarachnoid hemorrhage with a total duration of 62.5 hours. Correlations of Mx and TOx over time varied markedly among individual recordings. However, time-averaging over the entire recording interval in each of the 51 recordings, we found correlations between Mx and TOx and between Mx and TOxA were highly significant. This correlation was even stronger after correction for multiple sampling for each patient, reaching r=0.81 for Mx and TOx and r=0.72 for Mx and TOxA.Near-infrared spectroscopy can be used to continuously assess cerebral autoregulation in adults after subarachnoid hemorrhage.