Meta‐analysis of the association between preoperative anaemia and mortality after surgery

Background Numerous published studies have explored associations between anaemia and adverse outcomes after surgery. However, there are no evidence syntheses describing the impact of preoperative anaemia on postoperative outcomes. Methods A systematic review and meta‐analysis of observational studies exploring associations between preoperative anaemia and postoperative outcomes was performed. Studies investigating trauma, burns, transplant, paediatric and obstetric populations were excluded. The primary outcome was 30‐day or in‐hospital mortality. Secondary outcomes were acute kidney injury, stroke and myocardial infarction. Predefined analyses were performed for the cardiac and non‐cardiac surgery subgroups. A post hoc analysis was undertaken to evaluate the relationship between anaemia and infection. Data are presented as odds ratios ( ORs ) with 95 per cent c.i. Results From 8973 records, 24 eligible studies including 949 445 patients were identified. Some 371 594 patients (39·1 per cent) were anaemic. Anaemia was associated with increased mortality ( OR 2·90, 2·30 to 3·68; I 2  = 97 per cent; P  < 0·001), acute kidney injury ( OR 3·75, 2·95 to 4·76; I 2  = 60 per cent; P  < 0·001) and infection ( OR 1·93, 1·17 to 3·18; I 2  = 99 per cent; P  = 0·01). Among cardiac surgical patients, anaemia was associated with stroke ( OR 1·28, 1·06 to 1·55; I 2  = 0 per cent; P  = 0·009) but not myocardial infarction ( OR 1·11, 0·68 to 1·82; I 2  = 13 per cent; P  = 0·67). Anaemia was associated with an increased incidence of red cell transfusion ( OR 5·04, 4·12 to 6·17; I 2  = 96 per cent; P  < 0·001). Similar findings were observed in the cardiac and non‐cardiac subgroups. Conclusion Preoperative anaemia is associated with poor outcomes after surgery, although heterogeneity between studies was significant. It remains unclear whether anaemia is an independent risk factor for poor outcome or simply a marker of underlying chronic disease. However, red cell transfusion is much more frequent amongst anaemic patients.