Leave the Blood at Home?

In severely injured multi-system trauma patients, the gold standard for volume replacement is blood – in a relatively balanced ratio between PRBCs, plasma, and platelets. Match this need for blood with the conceptual “golden hour” for acute resuscitation, and it is reasonable to hypothesize there might be added benefit to providing blood products as early as feasible – including during emergency transport. Many of the most critically injured patients with time delays to a trauma center require aeromedical evacuation, so blood products on the helicopter may be ideal.

Sounds good, but the outcomes here are unfortunately not.

This is an observational report from nine trauma systems utilizing aeromedical transport, five of whose helicopters carried blood products and four whose carried only crystalloid. There were 25,118 patients during the study period, 2,341 of whom were transported by helicopter, and 1,058 of whom met “high risk” criteria. Approximately half of these were transported with blood products available, and 142 (24%) of those received transfusion.

Unfortunately, there were vast differences and great heterogeneity between the groups with and without blood products available, including GCS, ISS, and “prehospital lifesaving interventions”. There were similarly profound differences between those receiving blood and those not. The unadjusted mortality outcomes generally followed lower GCS and worse ISS, as one would expect. The authors then attempted a propensity-match analysis to dredge some signal from their data, but only 10% of their cohort could be parsed by their matching algorithm. Owing to only this small sample and the statistical techniques, no reliable difference in outcomes can be demonstrated.

The authors ultimately suggest a multicenter randomized trial will be required to adequately test whether the availability of blood has any mortality benefit. This is clearly the best strategy to improve our answer to this question, although it is prudent to recall non-obvious effect sizes in observational data potentially suggest only a very small magnitude of beneficial effect, if any. This must then be weighed against the important wastage of limited transfusion resources, which would require a non-trivial improvement in outcomes.

“Multicenter Observational Prehospital Resuscitation on Helicopter Study (PROHS)”