Original Research

Anemia Versus Transfusion: Does Blood Conservation Increase the Risk of Complications?

Am J Orthop. 2015 January;44(1):E11-E16

References

1. Leal-Noval SR, Rincón-Ferrari MD, García-Curiel A, et al. Transfusion of blood components and postoperative infection in patients undergoing cardiac surgery. Chest. 2001;119(5):1461-1468.

2. Hébert PC, Wells G, Blajchman MA, et al. A multicenter, randomized, controlled clinical trial of transfusion requirements in critical care. Transfusion Requirements in Critical Care Investigators, Canadian Critical Care Trials Group. N Engl J Med. 1999;340(6):409-417.

3. Carson JL, Altman DG, Duff A, et al. Risk of bacterial infection associated with allogeneic blood transfusion among patients undergoing hip fracture repair. Transfusion. 1999;39(7):694-700.

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5. Hill GE, Frawley WH, Griffith KE, Forestner JE, Minei JP. Allogeneic blood transfusion increases the risk of postoperative bacterial infection: a meta-analysis. J Trauma. 2003;54(5):908-914.

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Our study was designed to evaluate a conservative transfusion strategy used in orthopedic trauma patients. We hypothesized that the risk of anemia in these asymptomatic patients would be lower than the risk of transfusing asymptomatic patients in the perioperative period. In addition, we thought the level of anemia would play a less significant role in the postoperative complication rate relative to transfusion itself. Our results suggest that a more conservative transfusion strategy of allowing asymptomatic patients to become and remain anemic even to a Hgb level of 5 g/dL may be as safe as a more liberal transfusion strategy of keeping patients at a Hgb level higher than 7 g/dL. In general, the complication rate was 66% for transfused patients and 40% for nontransfused patients. These results remain significant after correcting for possible confounding factors, including age, sex, ISS, and number of surgeries.

The results of this study do not suggest that there may not be complications associated with anemia; a 40% complication rate even in the nontransfused group is high. One might expect that patients who had isolated injuries and never developed anemia with an Hgb level under 9 g/dL might have an even lower complication rate. In the group used for inclusion in this study, however, there was not a significant increased risk for patients who tolerated a lower anemia (Hgb, <7 g/dL), whereas transfusion to keep the Hgb level above 7 g/dL appeared to correlate with a significant risk of complication and appeared to be dose-dependent. It should be noted that the complications in both the transfusion and anemia groups are not necessarily related to transfusion or anemia, as many factors in a retrospective study cannot be controlled. These findings simply suggest that it might be as safe to use a conservative transfusion strategy as a liberal transfusion strategy in this patient population.

Although our study is retrospective, prospective randomized studies in the elderly and in the critical care population have shown conservative transfusion guidelines are at least as safe as liberal transfusion strategies.^2,11 One study randomized intensive care unit patients with Hgb levels under 9.0 g/dL to 2 groups, one with liberal and the other with restrictive protocols for pRBC unit transfusion.² The liberal group maintained Hgb levels between 10.0 and 12.0 g/dL, and the restricted group kept Hgb levels between 7.0 and 9.0 g/dL. Thirty-day mortality was significantly lower in less acutely ill patients and younger patients (<55 years old) in the restrictive group than in the liberal group. It was concluded that a restrictive strategy of RBC transfusion is at least as effective as, and possibly superior to, a liberal transfusion strategy in the critically ill when considering short- and long-term outcomes. Another prospective study randomized elderly patients (N = 2016) with hip fractures and cardiovascular risk factors to a liberal transfusion strategy (if Hgb level fell under 10 g/dL) or a restrictive transfusion strategy (if Hgb level fell under 8 g/dL). The study found no difference between the 2 groups.¹¹

The deleterious effect of allogeneic blood transfusion on the immune system is complex and has been linked to the down-regulation of cellular immunity, including decreased function of natural killer cells, decreased function of macrophages and monocytes, and increased numbers of suppressor T cells.^12,13 This minimized immune response has been associated with a multitude of infectious morbidities in various patient populations.⁷ A meta-analysis of 20 studies reviewing outcomes of the effects of transfusion on postoperative bacterial infection found strong evidence supporting a correlation.⁵ Their analysis found an OR of 5.3 (range, 5.0-5.4) for infectious complication after allogeneic transfusion in the trauma population, and an OR of 3.5 (range, 1.4-15.2) considering all patient populations.

Similar results showing increased risk of infectious morbidities associated with transfusion were found in other studies involving the critically ill, patients after hip arthroplasty, and cardiothoracic surgery and general trauma populations.^1,3,4,14,15 Furthermore, these results were seen in a dose-dependent response leading to increased incidence of complication with each unit of blood transfused.

Our study did not focus only on infection but included other complications (eg, cardiac, renal, and brain ischemia) that might be associated with anemia or transfusion. It is intuitive that anemia can cause ischemic events but less intuitive that allogeneic transfusion can also cause ischemic events because of the poor deformability of the cells due to storage, which can lead to “sludging” in capillaries throughout the body.¹⁶ This has been shown to be important in animal models, but it is unclear what poses more risk in humans—anemia without transfusion or the initial insult from transfusion, before the body clears the “waste” from stored cells and the remaining viable cells gain oxygen-carrying capacity.