The Relationship Between Pressure Reactivity and Cerebral Oximetry Indexes in Patients with Aneurysmal Subarachnoid Hemorrhage: A Single-Center Pilot Study.

Background: Patient differences from optimal mean arterial pressure (MAP) derived by a cerebral oximetry index (COx_a) are associated with outcome, but the validity of COx_a-derived MAP remains in question due to the lack of agreement with pressure reactivity index (PRx)-derived MAP. The study aimed to elucidate the relationship between PRx and COx_a to justify the use of COx_a and COx_a-derived MAP in patients with aneurysmal subarachnoid hemorrhage (aSAH).

Methods: This was a retrospective single-center study of six patients with aSAH with simultaneous near-infrared spectroscopy, intracranial pressure, and MAP monitoring. Repeated-measures Pearson correlation and Bland-Altman plot analysis were performed to compare PRx and COx_a and to compare PRx-derived MAP and COx_a-derived MAP. Coinciding changes in PRx and COx_a were compared, and the ability of COx_a to detect PRx-based autoregulation impairment was assessed over different time windows.

Results: Repeated-measures Pearson correlation analysis showed no correlation between PRx and COx_a (r = 0.06, p < 0.01). The correlation between PRx- and COx_a-derived MAP over 388 h was r = 0.50 (p < 0.01). The bias and upper and lower limits of agreement were - 1.60, + 20.24, and - 23.43 mm Hg, respectively. The shift in the overall distribution of moving correlation to higher values as the time-window length increased was more pronounced for COx_a than PRx (COx_a: 0.09-0.41, PRx: 0.00-0.15). When using a typical PRx threshold of 0.3, COx_a was found to be ineffective in identifying impaired autoregulation across all time windows (area under the receiver operating characteristic curve: 0.494-0.527).

Conclusions: The threshold applied to PRx should not be applied to COx_a. It is suggested to consider higher thresholds for COx_a than PRx in deriving the range for MAP calculations for continuous cerebral autoregulation assessment in aSAH. Further research is needed to optimize the MAP derived from PRx and COx_a based on specific monitoring targets.