In some circles, ‘wuntwuntwun’ is in danger of becoming the new dogma of trauma fluid replacement (ie. 1 unit of plasma and 1 unit of platelets for every unit of red cells). Since it takes longer to thaw some plasma than it does to throw in some O negative packed red cells, some really sick patients may be dead before they get the plasma, biasing comparisons that show a reduced mortality in patients who were still alive to receive plasma. This ‘survivor bias’ has been suggested as a reason that high plasma:red cell ratios are associated with mortality reduction, although this has been challenged.
The survivor bias explanation receives some new support by the following (small) study from Journal of Trauma:
BACKGROUND: In light of recent data, controversy surrounds the apparent 30-day survival benefit of patients achieving a fresh frozen plasma (FFP) to packed red blood cell (PRBC) ratio of at least 1:2 in the face of massive transfusions (MT) (≥10 units of PRBC within 24 hours of admission). We hypothesized that initial studies suffer from survival bias because they do not consider early deaths secondary to uncontrolled exsanguinating hemorrhage. To help resolve this controversy, we evaluated the temporal relationship between blood product administration and mortality in civilian trauma patients receiving MT.
METHODS: Patients requiring MT over a 22-month period were identified from the resuscitation registry of a Level I trauma center. Shock severity at admission and timing of shock-trauma admission, blood product administration, and death were determined. Patients were divided into high- and low-ratio groups (≥1:2 and<1:2 FFP:PRBC, respectively) and compared. Kaplan-Meier analysis and log-rank test was used to examine 24-hour survival.
RESULTS: One hundred three patients (63% blunt) were identified (66 high-ratio and 37 low-ratio). Those patients who achieved a high-ratio in 24 hours had improved survival. However, severity of shock was less in the high-group (base excess: -8.0 vs. -11.2, p=0.028; lactate: 6.3 vs. 8.4, p=0.03). Seventy-five patients received MT within 6 hours. Of these, 29 received a high-ratio in 6 hours. Again, severity of shock was less in the high-ratio group (base excess: -7.6 vs. -12.7, p=0.008; lactate: 6.7 vs. 9.4, p=0.02). For these patients, 6-hour mortality was less in the high-group (10% vs. 48%, p<0.002). After accounting for early deaths, groups were similar from 6 hours to 24 hours.
CONCLUSIONS: Improved survival was observed in patients receiving a higher plasma ratio over the first 24 hours. However, temporal analysis of mortality using shorter time periods revealed those who achieve early high-ratio are in less shock and less likely to die early from uncontrolled hemorrhage compared with those who never achieve a high-ratio. Thus, the proposed survival advantage of a high-ratio may be because of selection of those not likely to die in the first place; that is, patients die with a low-ratio not because of a low-ratio.
The authors state “The current study underscores the need for well-designed prospective studies to address the important question of which ratio results in improved survival and stresses the importance of timing of blood product administration as this may impact survival.“
Improved survival after hemostatic resuscitation: does the emperor have no clothes?
J Trauma. 2011 Jan;70(1):97-102