LAUSR

Learning Objectives: Brain death (BD) is a clinical diagnosis occasionally requiring ancillary testing. Cerebral near-infrared spectroscopy (NIRS) measures regional cerebral oxygenation (rScO2). We analyzed changes in rScO2 and cerebral autoregulation (CA) in comatose patients as they progressed to BD. Methods: Retrospective analysis of 5 comatose patients who progressed to BD while undergoing continuous CA monitoring using NIRS. Cerebral oximetry index (COx) was calculated as the moving correlation between the slow waves of the rScO2 and mean arterial pressure (MAP). Associations between rScO2 and COx pre and post-BD were assessed using mixed random effects models with random intercept. Model was adjusted for hemoglobin and arterial pCO2. Results: Primary diagnosis was supratentorial in 4 (3 traumatic, 1 anoxic brain injury) and infratentorial in 1 (basilar artery occlusion). Best clinical exam pre-BD during monitoring was absent brainstem reflexes in 3, lower cranial nerve reflexes in 1 and sluggish pupillary responses in 1. Three patients had a clinical BD diagnosis and two had ancillary testing (SPECT scans). Median (IQR) duration of monitoring for the clinical BD group was 10 (12.5) hours (N=55 hourly observations) and for the ancillary testing group 12.5 (12) hours (N=46 observations). Median (IQR) rScO2 post-BD diagnosis was significantly higher, 71 (6); compared to before the first brain death exam, 61 (8), p=0.007. Clinical BD was associated with higher rScO2 compared to patients diagnosed with ancillary testing, median rScO2 72 (6.5) vs 63 (10), p=0.005; there was no significant difference in COx (p=0.48). In all patients, COx was significantly higher following the first brain death exam compared to before; median (IQR) COx 0.22(0.18) vs 0.047(0.12) p=0.036, N=101 observations. There was no significant difference in COx and rScO2 between first and second BD exam (p=0.49 and p=0.93, respectively, N=59 observations). Conclusions: In patients with imminent BD, we observed loss of CA and increase in rScO2, consistent with decrease in cerebral metabolic rate.