Background and Goal of Study: Acute kidney injury (AKI) is commonly seen in the perioperative period and is associated with high morbimortality. It has been correlated with perioperative anaemia possibly due to less oxygen transport capacity. The aim of this study was to examine the association between postoperative anaemia and AKI in major orthopedic surgery.

Materials and methods: Medical records from patients submitted to elective orthopedic surgery from May to December 2012 were retrospectively reviewed, using a database from a previous study, with Local Ethics Committee approval. Exclusion criteria: minor surgery, chronic kidney disease (CKD) under haemodialysis, serum creatinine (SCr) > 1.6 mg/dL for men and > 1.4 mg/dL for women (without CKD), intraoperative mean arterial pressure (MAP) < 55 mmHg and incomplete records. Patient's characteristics, comorbidities, albumin [Alb] and perioperative data were collected. AKI was defined as an increment of SCr baseline of ≥ 0.3 mg/dL or ≥ 50% within 48h (AKI Network). Anaemia was considered for haemoglobin (Hb) levels < 10.0 g/dl. Descriptive and statistical analysis was performed using SPSS® 21.0 (χ2, Fisher Exact and Mann-Whitney U tests) with 95% confidence interval. A simple binary logistic regression was performed to identify independent risk factors for AKI.

Results and discussion: 196 from 307 were excluded and 111 were included (Anaemia Group [An]= 46; Non-anaemia Group [NAn]= 65). Hb levels 48h after surgery were 9.04 ± 0.83 and 12.06 ± 1.49 g/dL in An and NAn, respectively. Groups also differed on age (An: 65.57 ± 16,28 vs NAn: 57.69 ± 17,82, p= 0.019), previous CKD (An: 10.9% vs NAn: 0%, p= 0.011) and Alb (An: 3.03 ± 0.50 vs NAn: 3.41 ± 0.46, p= < 0.001). The mean SCr levels before surgery were 0.87 ± 0.38 and 0.85 ± 0.19 mg/dL in the An and NAn, respectively. 5.4% developed AKI. The AKI incidence was higher in the anemia group (An: 8.7% vs NAn: 3.1%), but without statistical significance (p= 0.23). Univariate analysis identified age (OR 1.11, 95% CI 1.00 to 1.23, p= 0.04) as an independent predictor of AKI.

Conclusions: A statistically significant association between postoperative anaemia and AKI was not established, despite the higher incidence in the anaemia group. Increasing age was independently associated with an increased likelihood of exhibiting AKI. It would be necessary to develop a large and controlled prospective study in order to clarify this tendencies.

Postoperative anaemia and acute kidney injury: a retrospective study in major orthopedic surgery