Clinical paperPrognostic values of gray matter to white matter ratios on early brain computed tomography in adult comatose patients after out-of-hospital cardiac arrest of cardiac etiology☆
Introduction
Although recent advances in post-cardiac arrest care have been revolutionary for cardiac arrest survivors,1, 2 45–70% of the survivors still suffer from severe neurologic deficits or die from brain injury.3, 4, 5 Thus, early methods to accurately predict patient outcomes would be useful in making therapeutic decisions and titrating therapy. Various parameters have been used for prognostication in comatose cardiac arrest survivors.6, 7, 8 However, accurate outcome prediction remains difficult, particularly within 24 h of cardiac arrest.
Brain computed tomography (CT) is frequently performed early following restoration of spontaneous circulation (ROSC) to exclude primary brain injury that could result in cardiac arrest and coma. Cerebral edema, a marker of brain injury associated with cardiac arrest, is seen as a loss of gray matter to white matter differentiation on brain CT images. Several previous studies found that gray matter to white matter ratio (GWR), calculated by dividing densities of gray matter by those of white matter, was significantly lower in cardiac arrest survivors with poor outcome relative to patients with good outcome, and thus that decreased GWR could predict poor outcome in cardiac arrest patients.9, 10, 11, 12, 13, 14 Scheel et al.15 evaluated the prognostic performance of GWR in 98 cardiac arrest survivors, and found a strong association of a low GWR with poor outcome. However, the ability of the GWR to predict outcomes in comatose patients after out-of-hospital cardiac arrest (OHCA) of cardiac etiology needs to be reassessed. Outcomes after OHCA of non-cardiac etiology are generally poor compared to OHCA of cardiac etiology.16, 17, 18 However, previous studies have included cardiac arrests of both etiologies, and did not consider etiology-based differences.9, 10, 11, 12, 13, 14, 15 For example, in the study by Scheel et al.,15 the arrest etiology was cardiac only in 53% of included subjects.
In this study, we sought to evaluate if the GWR on brain CT could help predict poor outcomes in adult comatose patients after OHCA of cardiac etiology.
Section snippets
Data source and population
This was a retrospective observational study using data from the Korean Hypothermia Network (KORHN) retrospective registry, which is a web-based, multicenter registry collection of data from adult (≥18 years) comatose OHCA survivors treated with therapeutic hypothermia (TH).19 Twenty-four hospitals throughout the Republic of Korea participated in the registry. The Institutional Review Board of each institution approved the study protocol before data collection. Informed consent was waived
Patients demographics
Of 930 patients with cardiac arrest in the registry, 564 were classified as OHCA of cardiac etiology. Of these 564 patients, 319 underwent brain CT scan within 24 h after ROSC. We excluded 21 patients with inadequate CT images for cerebral density measurements (poor quality, artifact) and 15 whose CT scans indicated previous surgery, infarction, or severe cerebral atrophy. Thus, 283 patients were included in this study. The clinical characteristics of these patients are summarized in Table 1.
Discussion
In this cohort of comatose adult patients after OHCA of cardiac etiology, GWRs on brain CT were significantly associated with outcomes. However, the GWRs demonstrated poor predictive value (AUC of 0.571 to 0.621), and the contribution of GWRs was not helpful in predicting poor outcomes.
Previous studies have indicated that the GWR from brain CT is a useful tool for predicting poor outcomes in comatose cardiac arrest survivors.10, 11, 12, 13 Choi et al.10 showed in 28 comatose cardiac arrest
Conclusions
In this study, the GWR could predict poor outcomes with statistical significance. However, given its poor predictive value, the GWR from early brain CT does not seem sufficiently useful as a predictor of poor outcomes in comatose adult patients after OHCA of cardiac etiology.
Conflict of interest statement
The authors have no conflict of interest.
Acknowledgements
We thank all the KORHN investigators and their hospitals for their participation in this study.
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A Spanish translated version of the summary of this article appears as the Appendix in the final online version at http://dx.doi.org/10.1016/j.resuscitation.2015.07.027.