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

BackgroundNumerous 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. MethodsA 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. ResultsFrom 8973 records, 24 eligible studies including 949445 patients were identified. Some 371594 patients (391 per cent) were anaemic. Anaemia was associated with increased mortality (OR 290, 230 to 368; I-2=97 per cent; P<0001), acute kidney injury (OR 375, 295 to 476; I-2=60 per cent; P<0001) and infection (OR 193, 117 to 318; I-2=99 per cent; P=001). Among cardiac surgical patients, anaemia was associated with stroke (OR 128, 106 to 155; I-2=0 per cent; P=0009) but not myocardial infarction (OR 111, 068 to 182; I-2=13 per cent; P=067). Anaemia was associated with an increased incidence of red cell transfusion (OR 504, 412 to 617; I-2=96 per cent; P<0001). Similar findings were observed in the cardiac and non-cardiac subgroups. ConclusionPreoperative 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. Associated with poor outcome