Factors associated with postoperative acute kidney injury after hip fractures in elderly patients

Objectives: Acute kidney injury (AKI) is a rare but serious complication after hip fractures. The aim of this study was to evaluate the incidence and the risk factors of postoperative AKI after hip fractures. Methods: From January 2011 to December 2016, 550 patients who underwent surgery of hip fractures at our institution were retrospectively reviewed. AKI was defined and classified by AKI Network (AKIN) Classification/Staging System. The incidence, mortality, and risk factors of postoperative AKI were investigated. Receiver operating characteristic curve analysis was conducted to evaluate the ability of markers in predicting AKI. Results: The incidence of postoperative AKI was 4.4% (25 cases). The mean onset of postoperative AKI was 8.0 +/- 5.3 days and recovered after 7.0 +/- 4.2 days after the occurrence of AKI. Of 25 patients with AKI, 6 patients (24.0%) died within 1 year after surgery. The independent risk factors for postoperative AKI are the estimated blood loss (EBL) (odds ratio (OR) 1.64; 95% confidence interval (CI) 1.33-2.58; p < 0.01) and postoperative level of albumin (OR 1.77; 95% CI 1.52-2.74; p < 0.01). The cutoff value of the serum albumin was <2.8 g/dL with a sensitivity of 88.0% and a specificity of 77.1%. The cutoff value of EBL was <766.5 mL with a sensitivity of 84.0% and a specificity of 66.3%. Conclusion: Postoperative AKI after hip fractures had low incidences (4.4%) but high mortality (24.0%). The postoperative AKI was correlated with blood loss and low postoperative albumin levels.