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Background
Iron deficiency (ID) is the leading cause of anemia worldwide. The prevalence of preoperative ID ranges from 23 to 33%. Preoperative anemia is associated with worse outcomes, making it important to diagnose and treat ID before elective surgery. Several studies indicated the effectiveness of intravenous iron supplementation in iron deficiency with or without anemia (ID(A)). However, it remains challenging to establish reliable evidence due to heterogeneity in utilized study outcomes. The development of a core outcome set (COS) can help to reduce this heterogeneity by proposing a minimal set of meaningful and standardized outcomes. The aim of our systematic review was to identify and assess outcomes reported in randomized controlled trials (RCTs) and observational studies investigating iron supplementation in iron-deficient patients with or without anemia.
Methods
We searched MEDLINE, CENTRAL, and ClinicalTrials.gov systematically from 2000 to April 1, 2022. RCTs and observational studies investigating iron supplementation in patients with a preoperative diagnosis of ID(A), were included. Study characteristics and reported outcomes were extracted. Outcomes were categorized according to an established outcome taxonomy. Quality of outcome reporting was assessed with a pre-specified tool. Reported clinically relevant differences for sample size calculation were extracted.
Results
Out of 2898 records, 346 underwent full-text screening and 13 studies (five RCTs, eight observational studies) with sufficient diagnostic inclusion criteria for iron deficiency with or without anemia (ID(A)) were eligible. It is noteworthy to mention that 49 studies were excluded due to no confirmed diagnosis of ID(A). Overall, 111 outcomes were structured into five core areas including nine domains. Most studies (92%) reported outcomes within the ‘blood and lymphatic system’ domain, followed by “adverse event” (77%) and “need for further resources” (77%). All of the latter reported on the need for blood transfusion. Reported outcomes were heterogeneous in measures and timing. Merely, two (33%) of six prospective studies were registered prospectively of which one (17%) showed no signs of selective outcome reporting.
Conclusion
This systematic review comprehensively depicts the heterogeneity of reported outcomes in studies investigating iron supplementation in ID(A) patients regarding exact definitions and timing. Our analysis provides a systematic base for consenting to a minimal COS.
Systematic review registration
PROSPERO CRD42020214247
Anaemia is a risk factor for several adverse postoperative outcomes. Detailed data about the prevalence of anaemia are not available over a long time-period in Germany. In this retrospective, observational, multicentre study, patients undergoing surgery in March in 2007, 2012, 2015, 2017 and 2019 were studied. The primary objective was the prevalence of anaemia at hospital admission. The secondary objectives were the association between anaemia and the number of units of red blood cells transfused, length of hospital stay and in-hospital mortality. A total of 23,836 patients were included from eight centres. The prevalence of pre-operative anaemia in patients aged ≥ 18 years decreased slightly from 37% in 2007 to 32.5% in 2019 (p = 0.01) and increased in patients aged ≤ 18 years from 18.8% in 2007 to 26.4% in 2019 (p > 0.001). The total amount of blood administered per 1000 patients decreased from 671.2 units in 2007 to 289.0 units in 2019. Transfusion rates in anaemic patients declined from 33.8% in 2007 to 19.1% in 2019 (p < 0.001) and in non-anaemic patients from 8.4% in 2007 to 3.4% in 2019 (p < 0.001). Overall, the mortality rate remained constant over the years: 2.9% in 2007, 2.1% in 2012, 2.5% in 2015, 1.9% in 2017 and 2.5% in 2019. In the presence of anaemia, mortality was significantly increased compared with patients without anaemia (OR 5.27 (95%CI 4.13–6.77); p < 0.001). Red blood cell transfusion was associated with an increased risk of mortality (OR 14.98 (95%CI 11.83–19.03); p < 0.001). Using multivariable linear regression analysis with fixed effects, we found that pre-operative anaemia (OR 2.08 (95%CI 1.42–3.05); p < 0.001) and red blood cell transfusion (OR 4.29 (95%CI 3.09–5.94); p < 0.001) were predictors of mortality but not length of stay (0.99 (95%CI 0.98–1.00) days; p = 0.12) and analysed years (2007 vs. 2019: OR 1.49 (95%CI 0.86–2.69); p = 0.07). Pre-operative anaemia affects more than 30% of surgical patients in Germany and multidisciplinary action is urgently required to reduce adverse outcomes.