ArticlesIndications for red blood cell transfusion in cardiac surgery: a systematic review and meta-analysis
Introduction
The aim of perioperative red blood cell transfusion in cardiac surgery is to improve or preserve oxygen delivery in patients with blood loss and anaemia. The decision to transfuse is complicated by several factors; severe anaemia and excessive blood loss are common,1, 2 and patients with cardiovascular disease have different transfusion requirements to other patient groups.3 Transfusion decisions in cardiac surgery are most commonly based on the severity of perioperative anaemia: guidelines recommend (grade C recommendation) highly restrictive transfusion thresholds with haemoglobin concentrations of 60–70 g/L.4, 5 These thresholds are largely based on the results of randomised controlled trials6, 7, 8 of non-cardiac surgery patients that suggest equivalence for restrictive transfusion threshold. They are also informed by evidence from observational studies9, 10, 11 showing strong associations between the reversal of severe anaemia by red blood cell transfusion and adverse clinical outcomes, such as death, acute lung injury, acute kidney injury, stroke, myocardial infarction, sepsis, and surgical site infections.
Red blood cell transfusion has important morbidity. Haemolytic transfusion reactions and transfusion-associated lung injury account for many deaths per year12 but a causal relationship has yet to be established between red blood cell transfusion and the adverse outcomes suggested by observational analyses. Severe anaemia, the main indication for transfusion, is an important predictor of adverse outcomes in patients undergoing cardiac surgery, who are probably already at the limits of their physiological reserve.2, 11 Clinical uncertainty as to the appropriate indications for transfusion is shown by wide variations in the number of transfusions done in cardiac surgery; ranging from 25% to 95% between hospitals according to cross-sectional studies.13
We systematically reviewed and critically assessed the evidence from randomised controlled trials and observational studies that are used to inform transfusion guidelines in cardiac surgery, to provide evidence to support clinical transfusion decisions and to inform the design of studies of appropriate transfusion indicators.
Section snippets
Study design and systematic review
A protocol was developed (appendix pp 21–28) that was restricted to randomised controlled trials and observational studies of transfusion in cardiac surgery, but because transfusion guidelines4, 5 are also based on randomised controlled trials of non-cardiac surgical patients, we subsequently decided to include these in this systematic review. Despite the limitations of comparing different study designs, we chose to compare randomised controlled trials and observational studies because they are
Results
We included six cardiac surgical randomised controlled trials (3352 patients),20, 21, 22, 23, 24, 25 19 non-cardiac surgical randomised controlled trials (8361 patients),3, 6, 7, 8, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40 and 39 cardiac surgical observational studies (232 806 patients; figure 1).9, 10, 11, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76 All cardiac surgical
Discussion
Our meta-analysis has shown that estimated effects of red blood cell transfusion differed greatly between cardiac surgical randomised controlled trials, non-cardiac surgical randomised controlled trials, and observational studies. In randomised controlled trials of adult patients undergoing cardiac surgery, the odds ratio for mortality favoured a liberal red blood cell transfusion strategy rather than a restrictive transfusion strategy, but the difference between strategies was not
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