Acute and chronic kidney disease in elderly patients with hip fracture: prevalence, risk factors and outcome with development and validation of a risk prediction model for acute kidney injury

Abstract

Background: Hip fracture is a common injury in older people with a high rate of postoperative morbidity and mortality. This patient group is also at high risk of acute kidney injury (AKI) and chronic kidney disease (CKD), but little is known of the impact of kidney disease on outcome following hip fracture.

Methods: An observational cohort of consecutive patients with hip fracture in a large UK secondary care hospital. Predictive modelling of outcomes using development and validation datasets. Inclusion: all patients admitted with hip fracture with sufficient serum creatinine measurements to define acute kidney injury. Main outcome measures - development of acute kidney injury during admission; mortality (in hospital, 30-365 day and to follow-up); length of hospital stay.

Results: Data were available for 2848 / 2959 consecutive admissions from 2007-2011; 776 (27.2%) male. Acute kidney injury occurs in 24%; development of acute kidney injury is independently associated with male sex (OR 1.48 (1.21 to 1.80), premorbid chronic kidney disease stage 3B or worse (OR 1.52 (1.19 to 1.93)), age (OR 3.4 (2.29 to 5.2) for >85 years) and greater than one major co-morbidities (OR 1.61 (1.34 to 1.93)). Acute kidney injury of any stage is associated with an increased hazard of death, and increased length of stay (Acute kidney injury: 19.1 (IQR 13 to 31) days; no acute kidney injury 15 (11 to 23) days). A simplified predictive model containing Age, CKD stage (3B-5), two or more comorbidities, and male sex had an area under the ROC curve of 0.63 (0.60 to 0.67).

Conclusions: Acute kidney injury following hip fracture is common and associated with worse outcome and greater hospital length of stay. With the number of people experiencing hip fracture predicted to rise, recognition of risk factors and optimal perioperative management of acute kidney injury will become even more important.

Keywords: Acute kidney injury (AKI); Hip fracture; Hospital length of stay; KDIGO creatinine criteria; Kidney function; Mortality; Postoperative AKI; Surgery; Surgical complication.

Fig. 1

Multivariate odds ratios of developing AKI following admission with hip fracture

Fig. 2

Kaplan Meier plot of cumulative probability of mortality day adjusted for age and gender and stratified for AKI severity

Fig. 3

Kaplan Meier plot of cumulative probability of mortality day adjusted for age and gender and stratified for CKD severity

Fig. 4

Multivariate odds ratios of 30-day mortality following admission with hip fracture

Fig. 5

Calibration plot for model 1. Data for the full dataset are shown in grey, for the training set in green and the testing set in blue. The area of the points is proportional to the number of cases in each group. The line represents the line of equality, where observed and predicted outcomes are equal

Fig. 6

Calibration plot for the Nottingham Hip Fracture – Risk Score for Kidney Injury (NH-RISK). Data for the full dataset are shown in grey, for the training set in green and the testing set in blue. The area of the points is proportional to the number of cases in each group. The line represents the line of equality, where observed and predicted outcomes are equal