BACKGROUND
Survival is significantly reduced by either hypotension or hypoxia during the prehospital management of major traumatic brain injury (TBI). However, only a handful of small studies have investigated the influence of the combination of both hypotension and hypoxia occurring together. Objective: In patients with major TBI, we evaluated the associations between mortality and prehospital hypotension and hypoxia, both separately and in combination.
METHODS
All moderate/severe TBI cases in the pre-implementation cohort of the Excellence in Prehospital Injury Care (EPIC) Study (a statewide, before/after, controlled study of the impact of implementing the prehospital TBI treatment guidelines) from 1/1/07–3/31/14 were evaluated [exclusions: age<10 years; prehospital oxygen saturation ≤10%; prehospital systolic blood pressure (SBP) <40 or >200mmHg]. The relationship between mortality and hypotension (SBP <90mmHg) and/or hypoxia (saturation <90%) was assessed using multivariable logistic regression, controlling for Injury Severity Score, head region severity, injury type (blunt versus penetrating), age, sex, race, ethnicity, payer, inter-hospital transfer, and trauma center.
RESULTS
Among the 13,151 cases that met inclusion criteria [Median age: 45; Male: 68.6%], 11,545 (87.8%) had neither hypotension nor hypoxia, 604 (4.6%) had hypotension only, 790 (6.0%) had hypoxia only, and 212 (1.6%) had both hypotension and hypoxia. Mortality for the four study cohorts was 5.6%, 20.7%, 28.1%, and 43.9%, respectively. The crude and adjusted odds ratios (cOR/aOR) for death within the cohorts, utilizing the patients with neither hypotension nor hypoxia as the reference, were 4.4/2.5, 6.6/3.0, and 13.2/6.1, respectively. Evaluation for an interaction between hypotension and hypoxia revealed that the effects are additive on the log odds of death.
CONCLUSION
In this statewide analysis of major TBI, combined prehospital hypotension/hypoxia were associated with dramatically increased mortality. This effect on survival persisted even after controlling for multiple potential confounders. In fact, the adjusted odds of death in patients with both hypotension and hypoxia was more than two times greater than those with either hypotension or hypoxia alone. These findings seem supportive of the emphasis on aggressive prevention and treatment of hypotension and hypoxia reflected in the current EMS TBI treatment guidelines but clearly reveal the need for further study to determine their impact on outcome.