Computed tomography-estimated specific gravity at hospital admission predicts 6-month outcome in mild-to-moderate traumatic brain injury patients admitted to the intensive care unit.

BACKGROUND: It is clear that patients with a severe traumatic brain injury (TBI) develop secondary, potentially lethal neurological deterioration. However, it is difficult to predict which patients with mild-to-moderate TBI (MM-TBI), even after intensive care unit (ICU) admission, will experience poor outcome at 6 months. Standard computed tomography (CT) imaging scans provide information that can be used to estimate specific gravity (eSG). We have previously demonstrated that higher eSG measurements in the standard CT reading were associated with poor outcomes after severe TBI. The aim of this study was to determine whether eSG of the intracranial content predicts 6-month outcome in MM-TBI.

METHODS: We analyzed admission clinical and CT scan data (including eSG) of 66 patients with MM-TBI subsequently admitted to our neurosurgical ICU. Primary outcome was defined as a Glasgow Outcome Scale score of 1 to 3 after 6 months. Discriminating power (area under the receiver operating characteristic curve [ROC-AUC], 95% confidence interval) of eSG to predict 6-month poor outcome was calculated. The correlation of eSG with the main ICU characteristics was then compared.

RESULTS: Univariate and stepwise multivariate analyses showed an independent association between eSG and 6-month poor outcome (P = 0.001). ROC-AUC of eSG for the prediction of 6-month outcomes was 0.87 (confidence interval: 0.77-0.96). Admission eSG values were correlated with the main ICU characteristics, specifically 14-day mortality (P = 0.004), length of mechanical ventilation (P = 0.01), length of ICU stay (P = 0.045), and ICU procedures such as intracranial pressure monitoring (P < 0.001).

CONCLUSIONS: In this MM-TBI cohort admitted to the ICU, eSG of routine CT scans was correlated with mortality, ICU severity, and predicted 6-month poor outcome. An external validation with studies that include the spectrum of TBI severities is warranted to confirm our results.