MedWire News: Many studies advocating use of a 1:1 ratio of fresh frozen plasma (FFP) to erythrocytes in trauma patients needing massive transfusion are prone to survivor bias, report researchers.

"On the other hand, the bias cannot be used to dismiss all of the available data to date," say Anthony Ho (Prince of Wales Hospital, Hong Kong) and colleagues. "Doing so is cherry-picking and spoils the debate."

Survivor bias in observational studies of transfusions in trauma patients comes about from the fact that, under current transfusion protocols, patients who survive for longer are able to receive more FFP and are thus categorized as having received a high ratio of FFP to erythrocytes, whereas those who die early receive less FFP.

But limiting analyses to patients who survive the first few hours excludes many who die of exsanguination (fatal blood loss) and could potentially have benefited from increased amounts of FFP, possibly creating a survivor bias against a high FFP-to-erythrocytes ratio.

When Ho et al analyzed studies of blood ratios in trauma patients they found no randomized controlled trials and 26 observational studies including 6655 patients. Four studies were conducted in military personnel and 21 studies found in favor of a high FFP-to-erythrocytes ratio.

Of these, 11 studies showed survivor bias in favor of a high FFP-to-erythrocytes ratio, whereas 10 studies, all conducted in civilians, were judged to lack survivor bias or to have survivor bias against a high FFP-to-erythrocytes ratio.

Five studies, all in civilians, lacked survivor bias or had survivor bias against a high FFP-to-erythrocytes ratio and found no benefit for a high FFP-to-erythrocytes ratio. The researchers note that no study found a high FFP-to-erythrocytes ratio to be associated with decreased survival.

In a related editorial, Richard Weiskopf (University of California, San Francisco, USA) observes that the Prospective Randomized Optimum Platelet and Plasma Ratios (PROPPR) trial will address the issue in a multicenter, randomized trial in civilian trauma patients.

But he adds: "Whatever the results of the PROPPR trial, it will not be the end of the line. The logical question that should arise is that if a ratio of transfused red cells to plasma of 1:1 is beneficial, then why not transfuse whole blood, thus reducing substantially recipient exposures to donors?"

Weiskopf says that only a few very small studies have assessed whole blood transfusion, partly because of the lack of available whole blood. He concludes: "The blood banking community is likely to get on board only if they are convinced by data, surgeons, anesthesiologists, intensivists, and other clinicians caring for trauma patients."

MedWire (www.medwire-news.md) is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2012

Free abstract