Modern trauma care has essentially, based on several articles published in the Journal of Trauma, migrated to 1:1 ratios of FFP to PRBC in massive transfusion. This was motivated in part by the outcomes observed in battlefield trauma associated with the use of whole blood. However, multiple individuals feel the true answer might lay somewhere in between – and that the observed association between equivalent transfusion ratios and survival is related to “survival bias”. In essence, trauma patients arriving the ED receive blood first – and the FFP only arrives if they survive long enough to receive it. Therefore, on retrospective analysis, the data is automatically skewed in favor of the folks who receive FFP, simply because they survived long enough to do so.
This is another retrospective review, but one that attempts to control for time-dependent exposure in the transfusion ratio. These authors generate hour-by-hour transfusion ratios throughout the first 48 hours of a patient’s hospital stay – and use these sort of time-dependent ratios to make their associations with outcomes. Using the “conventional” model – as other studies have done – there is a 2.50-fold (1.54 – 4.05) risk of death among patients with a low FFP:RBC ratio. With their “time-dependent” model, the adjusted hazard rate is only 1.25-fold (0.78 – 2.00).
There are, of course, a few problems with methods. Emergency transfusions where RBCs were in the Emergency Department had time imputed from retrospective analysis, rather than from blood bank issue time. In the 10 randomly selected patients the authors performed chart review to validate their analysis, they saw a median difference of 0.14 hours between issue time and transfusion time – but with an interquartile range of 0.0 – 2.5 hours. This means some of their analysis is based off extraordinarily imprecise data. Then, the reviewing anesthesiologist performing the outcome review was not consistently blinded to the transfusion ratio of the patient – which potentially biases the results in whatever manner suits the authors.
In the end, it’s another inconclusive data point in the massive transfusion literature. Luckily, there is a prospective trial already in progress.
“Effect of Plasma-to-RBC Ratios in Trauma Patients: A Cohort Study With Time-Dependent Data”
http://www.ncbi.nlm.nih.gov/pubmed/23782963