Interactive Effect between On-Scene Hypoxia and Hypotension on Hospital Mortality and Disability in Severe Trauma.

BACKGROUND: It is unclear whether effect size of the hypoxia is different on in-hospital mortality and disability according to hypotension status in the field.

METHODS: Adult severe trauma (ST) patients during 2012-13 who were treated by emergency medical services (EMS) and had abnormal revised trauma scores in the field or who had positive trauma triage criteria were analyzed. Exposure was hypoxia (<94%) measured by EMS. End points were hospital mortality and disability defined as a Glasgow Outcome Scale that decreased by 2 points or more. Multivariable logistic regression with interaction model between hypoxia and hypotension was used for outcomes to calculate the adjusted odds ratios (AOR) with 95% confidence intervals (95% CIs) after adjusting for potential confounders.

RESULTS: A total of 17,406 EMS-ST patients were analyzed. Of those, 2,598 (14.9%) died, and 3,292 (21.5%) were considered disabled at discharge. The total hypoxia group showed higher mortality and disability indices (35.7 and 51.2%) than the non-hypoxia group (10.7 and 15.9%) (each p-value < 0.0001). The AOR of hypoxia was 2.15 (1.92-2.40) for mortality and was 1.97 (1.75-2.21) for disability. In the interaction model, AORs for mortality by hypoxia in the hypotensive and non-hypotensive groups were 2.66 (2.32-3.04) and 1.74 (1.61-1.87), respectively (P < 0.0001 for interaction). The AORs for disability in the hypotensive and non-hypotensive groups were 2.17 (1.87-2.53) and 1.55 (1.42-1.69), respectively (P < 0.0001 for interaction).

CONCLUSIONS: The effect of hypoxia was much greater in the hypotensive group than in the non-hypotensive group both in terms of mortality and disability.