Relationship Between Brain Tissue Oxygen and Near-Infrared Spectroscopy in Patients with Nontraumatic Subarachnoid Hemorrhage.

Continuous monitoring of cerebral oxygenation is one of the diagnostic tools used in patients with brain injury. Direct and invasive measurement of cerebral oxygenation with a partial brain oxygen pressure (PbtO) probe is promising but invasive. Noninvasive assessment of regional transcranial oxygen saturation using near-infrared spectroscopy (NIRS) may be feasible. The aim of this study was to evaluate the interchangeability between PbtO and NIRS over time in patients with nontraumatic subarachnoid hemorrhage. This retrospective study was performed in a neurocritical care unit. Study participants underwent hourly PbtO and NIRS measurements over 72 h. Temporal agreement between markers was described by their pointwise correlation. A secondary analysis assessed the structure of covariation between marker trajectories using a bivariate linear mixed model. Fifty-one patients with subarachnoid hemorrhage were included. A total of 3362 simultaneous NIRS and PbtO measurements were obtained. The correlation at each measurement time ranged from - 0.25 to 0.25. The global correlation over time was - 0.026 (p = 0.130). The bivariate linear mixed model confirmed the lack of significant correlation between the PbtO and NIRS measurements at follow-up. NIRS was unable to detect PbtO values below 20 mm Hg (area under the receiver operating characteristic curve 0.539 [95% confidence interval 0.536-0.542]; p = 0.928), and percentage changes in NIRS were unable to detect a decrease in PbtO ≥ 10% (area under the receiver operating characteristic curve 0.615 [95% confidence interval 0.614-0.616]; p < 0.001). PbtO and NIRS measurements were not correlated. There is no evidence that NIRS could be a substitute for PbtO monitoring in patients with nontraumatic subarachnoid hemorrhage