Background: Studies of pre-hospital endotracheal intubation (ETI) from single EMS systems have shown contradictory results, which may represent local differences in paramedic training and experience. An alternative hypothesis is that positive pressure ventilation increases mortality because positive pressure ventilation causes hypotension in severely injured hypovolemic patients.
Methods: A national sample (National Trauma Data Bank, 1994-2002) was used to minimize effects of local paramedic training and experience. All patients with pre-hospital GCS < 8 (most likely to warrant early ETI) and ISS > 16 (most likely to be hypovolemic) were included. Patients intubated in the field (pre-hospital group, n = 871) and in the emergency department (ED group, n = 6581) were compared. To determine whether pre-hospital ETI was an independent predictor of hypotension and mortality, logistic regression was used to control for potential confounders, including age, ISS, body region injured, AIS scores, pre-hospital IV fluids, and other variables. Physiologic variables were not used, as they may be influenced by ETI and positive pressure ventilation, and were therefore considered outcomes, rather than predictors.
Results: Groups were comparable in age, gender, anatomic distribution of injuries, likelihood of at least one severe injury (AIS >3) and other variables, except for head injury (ED 83%, pre-hospital 71%, p < 0.001) and ISS (ED 33 +/- 0.2, pre-hospital 36 +/- 0.6, p < 0.001). Patients intubated in the field were more likely to be hypotensive upon arrival in the ED (SBP < or = 90 mm Hg; ED 33%, pre-hospital 54%, p < 0.001), and had worse survival (ED 45% versus pre-hospital 24%, p < 0.001). Even after controlling for potential confounders, pre-hospital ETI was still an independent predictor of hypotension upon arrival in ED (OR 1.7, 95% CI 1.46 -2.09, p < 0.001) and decreased survival (OR 0.51, 95% C.I. 0.43-0.62, p < 0.001).
Conclusions: Pre-hospital endotracheal intubation in trauma patients is associated with hypotension and decreased survival. This may be mediated by the effect of positive pressure ventilation during hypovolemic states.