Statistical Analysis

Outcomes following dialysis-requiring AKI were compared between the periods; 2005–2006, 2007–2008, 2009–2010, and 2011–2012. Trends in patient characteristics were compared using the Cochrane-Armitage test. Durations of dialysis-requirement and hospital stay amongst patients surviving beyond hospital discharge were calculated in whole days in renal survivors. Statistical significance was defined as a two sided p-value <0.05. Analyses were performed using SAS software (versions 9.4, SAS Institute), and R version 2.15.2 (R Development Core Team). Summary results were reported with 95% confidence intervals (CI), means with standard deviations (SD), and medians with interquartile range (IQR). Odds ratios for one-year mortality and ESRD were calculated in multiple logistic regression analyses with adjustment for known risk factors associated with prognosis. As such, the models were adjusted for patient age, gender, dialysis modality, comorbidity, surgery, sepsis, mechanical ventilation, and circulatory support. Comorbidities included in the model were; non-insulin dependent and insulin-dependent diabetes, congestive heart failure, ischemic heart disease, cardiac arrhythmia, valvular heart disease, peripheral vascular disease, stroke, chronic obstructive pulmonary disease, solid and non-solid cancer, and chronic kidney disease. Preceding surgeries included in the model were any major cardiothoracic, gastric or orthopedic procedures.

Furthermore, odds ratios for one-year mortality and ESRD were also computed in various selected subpopulations. These included; gender-specific strata, age-specific strata, modality-specific strata, non-surgery-related and surgery-related strata, non-intensive care requiring and intensive care requiring strata, and Charlson Index Score stratified (<3, 3–6, and >6). In additional analyses, odds ratios were calculated for 90-day mortality and 90-day renal survival using multiple logistic regression analyses analogous to the principal analyses. As incidence of dialysis-requiring AKI in the general population was lowest in 2005, sensitivity analyses with exclusion of patients from the aforementioned year were performed to confirm the principal results; no differences were discernable. Finally, residual renal function was assessed in renal survivors by comparing the proportionate number of patients with significant (>20%) decrease in eGFR 90–365 days following index. Retrospective register based studies do not need ethical approval in Denmark; however, the Danish Data Protection Agency has approved use of data (ref. 2007-58-015 / I-suite nr 00916 GEH-2010-001).