A review of trauma patients taken to hospital by air ambulance

Introduction Doctors are being introduced on air ambulance services in the UK. Meaningful assessment of air ambulance services is difficult owing to inter-service variation. County air ambulance (CAA) (rebranded as Midland's Air Ambulance after this article was written) progressively introduced doctors into their service from 2006 providing an opportunity to gather data and quantify the sample size that will be required to assess their impact on patient survival. Method CAA trauma alerts to Selly Oak Hospital (the main receiving hospital for the service) between 1 January 2006-30 June 2007 were reviewed. Crew composition, mission data and patient notes were examined and the abbreviated injury score 98 and injury severity score were used to calculate the probability of survival. Survival outcome was ascertained at 90 days. Data analysis included survival analysis; Cox regression; logistic regression; tests for association (CI 95%, P<0.05). Post-hoc power calculations were undertaken. Results 299 cases were identified, 186 met the inclusion criteria. The probability of survival ranged between 5.56-99.48%. There was no statistically significant association found between crew composition and survival (P=0.355) and post-hoc power calculations showed 54 258 events would be required to assess this. If accepting 80% power and assuming our proportion of 14% mortality ± 5%, 800 events would be required in each arm of future studies. Conclusions Our post-hoc power calculations revealed that a national or multi-centre study is needed to assess this aspect of aircrew composition in order to prove or discount associations between crew composition and survival at 90 days. Now that a power estimate is available, designing adequately powerful studies will be possible; enabling monitoring the increasing deployment of this expensive resource and examining the effect of doctors on air ambulances. This is of increasing importance to assess as medically-led air ambulance missions increase.