Monday 31 July 2017

Every minute counts: Time to delivery of initial massive transfusion cooler and its impact on mortality. A misleading observational study.

This study was a planned subanalysis of the PROPPR trial. If you can remember, this was an RCT looking at a blood products transfusion ratio of 1:1:1 vs. 1:1:2 (platelets, plasma, PRBC’s) in trauma patients with exsanguinating haemorrhage. There was no difference in the primary outcome.

But the PROPPR trial also collected observational data on time to massive transfusion (MT) activation and time to blood product cooler arrival. Could mortality and other outcomes be predicted by these times? Time for some subanalysis…

I’ll start with the conclusion of this observational study;

“…every minute from time of massive transfusion protocol activation to time of initial cooler arrival increases odds of mortality by 5%.”

You will very likely hear this quoted in the future. Unfortunately, it is not only misleading but likely wrong.

First, it is not absolute mortality but rather “odds.” This concept of “odds” is challenging to comprehend and relies on relative numbers.

In addition, there was very likely residual confounding that was responsible for the differences in mortality. The timing of MT activation and cooler arrival was not randomized.

The authors did make attempts at a few adjusted analyses for some identified confounders such as injury severity, physiology etc. and this was a bit hit and miss. There were some statistical differences and some trends. But nothing very clear. Of course, these adjustments are always difficult and are based on many assumptions.

The authors then go on to discuss how their results may be analogous to STEMI teams, door-to-balloon time, stroke teams etc. All of this is a bit silly.

I don’t have an issue with recognizing the need for massive transfusion quickly and getting blood products to the bedside as fast as possible when needed. But this is based on common sense and not this study.

So, when you hear “it is proven that there is a 5% increase in the odds of mortality for each minute delay…” you can shake your head in either a 1:1:1 or 1:1:2 fashion.


No comments:

Post a Comment