Prehospital hypocapnia and poor outcome after severe traumatic brain injury.

Background: The Brain Trauma Foundation (BTF) Guidelines for prehospital management of traumatic brain injury (TBI) recommend a goal end-tidal carbon dioxide of 30 mm Hg to 35 mm Hg in patients without signs of herniation.

Methods: We examined prehospital concordance with BTF Guidelines, selected demographic and physiologic variables and outcomes for 100 consecutive admissions to a well-established Level I regional trauma center. All patients had blunt TBI with Glasgow Coma Score < or = 8 without signs of herniation. All were transported by helicopter by flight paramedics experienced with BTF Guidelines and the continuous wave form capnometer. Patients resumed spontaneous ventilation after intubation.

Results: Concordance (prehospital end-tidal carbon dioxide > 29 mm Hg) was achieved in 65 of 100 cases. Mortality was 29% (19 of 65) among those in whom guideline levels were achieved prehospital and 46% (16 of 35) in those in whom guideline levels were not achieved prehospital (odds ratio, 0.49; p = 0.10). The "achieved" group was younger (p = 0.02), with higher calculated probability of survival (p = 0.01). Intracranial pressure was maintained under intensive care within acceptable limits in the hospital in both groups but was significantly higher in the "not achieved" group (p = 0.05).

Conclusions: Our data, though not statistically significant, suggest that patients who are harder to keep within the guidelines in the field are more likely to die, because of more severe TBI or complication by other factors such as age or injury severity. Whether increased awareness of this phenomenon can improve outcomes is unknown but suggests an approach to future education and research.