ASA class is independently associated with 30-day mortality after mild traumatic brain injury with intracranial injury: a national retrospective cohort study

INTRODUCTION: Outcome assessment after mild traumatic brain injury (mTBI) has largely focused on acute injury severity, while the role of pre-injury health has received comparatively less attention. The American Society of Anesthesiologists (ASA) physical status classification provides a simple measure of pre-existing health and comorbidity that may be relevant to early outcomes after trauma. This study examined whether pre-injury ASA class is independently associated with short-term mortality after mTBI and compared these associations with those observed in trauma patients without brain injury (NTBI). METHODS: We conducted a nationwide retrospective study using the Swedish Trauma Registry (2018-2023). Adults (≥ 18 years) with Glasgow Coma Scale (GCS) > 12 were included and classified as mTBI (ICD-10 S06.0-S06.9) or NTBI (no S06 diagnosis, AIS head = 0, age-matched). The primary outcome was 30-day all-cause mortality. Associations between clinical variables and mortality were examined using univariable and multivariable logistic regression, with models specified a priori to separate age-ASA effects from injury-related adjustment. RESULTS: A total of 8,670 patients were included in the mTBI cohort and 26,001 in the age-matched cohort. The mTBI cohort had poorer health (ASA ≥ 3: 27% vs 24%), and more often injured by low-energy falls (28% vs 20%). Mortality was higher in mTBI (5% vs 2.8%), and outcomes poorer (Glasgow Outcome Scale 1-3: 23% vs 17%). Within the mTBI cohort, mortality was strongly associated with increasing age, higher ASA category, and greater intracranial injury severity. After adjustment for age and injury-related variables, ASA class remained independently associated with 30-day mortality. Specifically, compared to ASA 1 patients, those with ASA 2 had 2.8 times higher odds of 30-day mortality, ASA 3 patients had 4.3 times higher odds, and ASA 4 patients had 21 times higher odds. A graded association between ASA class and mortality was also observed in the NTBI cohort, although the pattern of injury-related covariates differed. CONCLUSIONS: Pre-injury health status, measured by the ASA class, was independently associated with 30-day mortality in patients with mild traumatic brain injury. Comparable associations in non-TBI trauma suggest that comorbidity and baseline health contribute substantially to early post-trauma mortality among awake trauma patients. ASA class may provide complementary information to traditional injury-based assessments, particularly in older patients, although further studies are needed to evaluate how such information can best inform clinical decision-making.