Prehospital Intubation in Severe Head Injury

A very interesting study appeared in the December issue of Prehospital and Disaster Medicine that challenges conventional wisdom concerning prehospital intubation of TBI patients, and appears to support the position of those who oppose prehospital intubation.

Researchers from the Division of Acute Care Surgery at UCLA retrospectively analyzed the charts of 1,105 patient who were admitted with isolated severe TBI (AIS +/>3, and/or GCS +<8) during an 8-year study period. 847 of those patients met all inclusion criteria, one of which was having an arterial blood gas sample drawn upon ED arrival. Rigorous propensity matching resulted in a cohort of 55 patients who were intubated in the field compared to a well-matched control group of 165 who were not. The primary outcome was mortality and secondary outcomes included admission blood gas profile, morbidity, and ICU and hospital lengths of stay.

The primary outcome result was not particularly surprising, though disappointing: patients intubated in the field had a significantly greater chance of dying than those who were not intubated in the field (69.1% vs 55.2%). More interesting, though, were two of the secondary outcomes: admission blood gases between the two groups were the same, with the exception a slightly lower Pa02 in the intubated patients vs. the non-intubated ones (187 mmHg vs. 213 mmHg). The incidence of pneumonia was exactly the same between the two groups: 5.5%. Intubated patients had higher rates of septic shock (14.5% vs. 4.2%).

This study convincingly calls into question the very rationale upon which prehospital intubation of head injured patients is based: the need to secure the airway and the need to control ventilation. With identical rates of pneumonia, aspiration was apparently not a problem in the non-intubated patients, and with the same BE, pH, and C02 levels and higher oxygen tensions in the non-intubated patients, ventilation and oxygenation was apparently not a problem in the non-intubated patients.

This is far from the first study to show worse outcomes in patients who are intubated in the field, and a common hypothesis has been that patients who are intubated are hyperventilated during transport (I have read of studies that found very low PaC02's on ED arrival in prehospitally-intubated patients, but I cannot find a reference right now). This study, however, shows that C02 tension does not necessarily tell the whole story.

The Brain Trauma Foundation has long taught that even brief episodes of hypotension or hypoxemia will dramatically increase mortality in TBI patients. In my experience, hypotension and hypoxemia are not at all uncommon during prehospital RSI's, and while these insults are usually transient, they are often severe. The BTF's evidence table addresses the importance of this. Poor control of hemodynamics and prevention of hypoxemia during and immediately after field intubation seems a likely explanation for the worsened outcomes in those patient.

One significant challenge to interpreting this type of research is that protocols, staffing models, initial and continuing paramedic training requirements, and QA/QI processes vary dramatically from EMS system to EMS system. With that in mind, it is unfortunate that there was no discussion by the authors as to what types of intubation protocols were used in the field. Presumably, most of these patients were intubated using RSI. Why weren't the non-intubated patients intubated? Did the non-intubated ones have unsuccessful attempts performed? Were the non-intubated patients not intubated because they were transported by EMT-B's, whereas the intubated ones were transported by EMT-P's? Did the intubated patients present to EMS with a lower GCS, whereas the non-intubated ones deteriorated during transport? What do the regional airway and RSI protocols look like? Such information may be useful to those who wish to consider these findings.

Dr. Minh Le Cong discussed this study in his excellent podcast.

1. Efstathios Karamanos, MD; Peep Talving, MD, PhD; Dimitra Skiada, MD; Melanie Osby, MD;Kenji Inaba, MD; Lydia Lam, MD, et al. Is Prehospital Intubation Associated With Improved Outcomes In Isolated Severe Head Injury? A Matched Cohort Analysis. Prehospital And Disaster Medicine. 2013 Dec 13:1-5
2. The Brain Trauma Foundation - Prehospital Severe TBI Guidelines