Abstract Body: Background
Cerebral edema following cardiac arrest can be quantified by measuring the ratio of grey matter to white matter radiodensity (GWR). Decreased GWR may reflect edema from irrecoverable neuronal cell death or reversible hyperemia driven by hypercapnia. We tested for an interaction between GWR and partial pressure of carbon dioxide (PCO2) predicting outcomes.

Methods
We identified comatose post-arrest patients treated at our single center between 2010 and 2023 who underwent brain computed tomography (CT) imaging within 24 hours and PCO2 measured within one hour of CT. We extracted demographics, GWR, and PCO2 from our prospective registry and electronic health record. We scaled and centered data, then fit a multivariate logistic model to quantify the interaction between GWR and PCO2 in predicting survival.

Results
Of 901 included patients, 356 (40%) were female, median [IQR] age was 61 [51-70], and 221 (25%) survived to discharge. CTs were obtained 4.18 [2.8-5.7] hours post-arrest. PCO2 was sampled within 36 median [24-47] minutes of CT. The median PCO2 was 47 [39-59] mmHg. GWR predicted survival (coefficient estimate 1.16, 95% confidence interval [CI], 0.91-1.44, p < 0.001, but PCO2 (-0.11, 95% CI -0.32-0.09, p = 0.29) did not. There was no significant interaction between GWR and PCO2 (0.009, 95% CI -0.24-0.29, p = 0.95).

Conclusion
There is no evidence of PCO2 modifying the association of early GWR with survival after resuscitation from cardiac arrest.