Feasibility of optic nerve sheath diameter measured on initial brain computed tomography as an early neurologic outcome predictor after cardiac arrest

Abstract

Objectives: Few parameters are available to predict neurologic outcome of post-cardiac arrest patients in the early stage of treatment. Optic nerve sheath diameter (ONSD) has been used to indirectly assess intracranial pressure. This study evaluated whether ONSD, an additional parameter in initial brain computed tomography (CT) scans, can be an early predictor of neurologic outcome in post-cardiac arrest patients.

Methods: A total of 112 cardiac arrest patients between November 2012 and October 2013 were identified. Ninety-eight comatose cardiac arrest patients were evaluated with brain CT. Of these patients, after exclusion of patients whose brain CT scans were done too late or with poor baseline neurology (Cerebral Performance Category [CPC] ≥ 3), 91 patients were included for this study. The parameters of initial brain CT, i.e., gray matter-to-white matter ratio (GWR) and ONSD, were measured after clinical care as part of a retrospective reanalysis of images. ONSD on brain CT was bilaterally measured 3 mm behind the eyeball at fixed window width and level and averaged to yield the mean value. The performance of ONSD to predict poor neurologic outcome (CPC = 3 to 5) was analyzed using multiple logistic regression analysis, receiver operating characteristic (ROC) curve analysis, and cross-tabulations.

Results: Twenty-three patients showed good neurologic outcomes at hospital discharge. Mean (±SD) ONSD was 5.6 (±0.3) mm in the good outcome group versus 6.3 (±0.5) mm in the poor outcome group (p < 0.001). After basic clinical covariates were controlled for, i.e., age, Glasgow Coma Scale (GCS) score (3 vs. 4-15), and time from collapse to return of spontaneous circulation (ROSC), ONSD (odds ratio [OR] = 2.1; 95% confidence interval [CI] = 1.1 to 3.9) and GWR (OR = 0.6; 95% CI = 0.4 to 0.9) were found to be significant factors for predicting poor neurologic outcome. ROC curve analysis showed that ONSD and GWR had areas under the ROC curve of 0.931 (95% CI = 0.87 to 0.98) and 0.922 (95% CI = 0.86 to 0.97), respectively. Combining the cutoff values of ONSD (6.21 mm, sensitivity = 56%; 95% CI = 43% to 68%) and GWR (1.23, sensitivity = 84%; 95% CI = 73% to 92%) to have 100% specificities, the sensitivity was improved to 92% (95% CI = 84% to 98%). Intrarater and interrater intraclass correlation coefficients between the investigators measuring ONSD were 0.888 and 0.833, respectively.

Conclusions: Optic nerve sheath diameter on initial brain CT correlated closely with the neurologic outcome of hypoxic ischemic encephalopathy and had good reliability. Additional prospective work may be justified evaluating the standardization and diagnostic performance in real time use as a predictive tool for neurologic outcome following cardiac arrest.

© 2014 by the Society for Academic Emergency Medicine.