The association between a quantitative computed tomography (CT) measurement of cerebral edema and outcomes in post-cardiac arrest-a validation study

Abstract

Aim: Previous studies have examined the association between quantitative head computed tomography (CT) measures of cerebral edema and patient outcomes reporting that a calculated gray matter to white matter attenuation ratio (GWR) of <1.2 indicates a near 100% non-survivable injury post-cardiac arrest. The objective of the current study was to validate whether a GWR <1.2 reliably indicates poor survival post-cardiac arrest. We also sought to determine the inter-rater variability among reviewers, and examine the utility of a novel GWR measurement to facilitate easier practical use.

Methods: We performed a retrospective analysis of post-cardiac arrest patients admitted to a single center from 2008 to 2012. Inclusion criteria were age ≥18 years, non-traumatic arrest, and available CT imaging within 24h after ROSC. Three independent physician reviewers from different specialties measured CT attenuation of pre-specified gray and white matter areas for GWR calculations.

Results: Out of 171 consecutive patients, 90 met the study inclusion criteria. Thirteen patients were excluded for technical reasons and/or significant additional pathology, leaving 77 head CT scans for evaluation. Median age was 66 years and 64% were male. In-hospital mortality was 65% and 70% of patients received therapeutic hypothermia. For the validation measurement, the intra-class correlation coefficient was 0.70. In our dataset, a GWR below 1.2 did not accurately predict mortality or poor neurological outcome (sensitivity 0.56-0.62 and specificity 0.63-0.81). A score below 1.1 predicted a near 100% mortality but was not a sensitive metric (sensitivity 0.14-0.20 and specificity 0.96-1.00). Similar results were found for the exploratory model.

Conclusion: A GWR <1.2 on CT imaging within 24h after cardiac arrest was moderately specific for poor neurologic outcome and mortality. Based on our data, a threshold GWR <1.1 may be a safer cut-off to identify patients with low chance of survival and good neurological outcome. Intra-class correlation among reviewers was moderately good.

Keywords: CT; Cardiac arrest; Cerebral edema; Computed tomography; Post-cardiac arrest; Prognostication.