U-Curve Association between Timing of Renal Replacement Therapy Initiation and In-Hospital Mortality in Postoperative Acute Kidney Injury

BACKGROUND Postoperative acute kidney injury (AKI) is associated with poor outcomes in surgical patients. This study aims to evaluate whether the timing of renal replacement therapy (RRT) initiation affects the in-hospital mortality of patients with postoperative AKI. METHODOLOGY This multicenter retrospective observational study, which was conducted in the intensive care units (ICUs) in a tertiary hospital (National Taiwan University Hospital) and its branch hospitals in Taiwan between January, 2002, and April, 2009, included adult patients with postoperative AKI who underwent RRT for predefined indications. The demographic data, comorbid diseases, types of surgery and RRT, and the indications for RRT were documented. Patients were categorized according to the period of time between the ICU admission and RRT initiation as the early (EG, ≦1 day), intermediate (IG, 2-3 days), and late (LG, ≧4 days) groups. The in-hospital mortality rate censored at 180 day was defined as the endpoint. RESULTS Six hundred forty-eight patients (418 men, mean age 63.0±15.9 years) were enrolled, and 379 patients (58.5%) died during the hospitalization. Both the estimated probability of death and the in-hospital mortality rates of the three groups represented U-curves. According to the Cox proportional hazard method, LG (hazard ratio, 1.527; 95% confidence interval, 1.152-2.024; P = 0.003, compared with IG group), age (1.014; 1.006-1.021), diabetes (1.279; 1.022-1.601; P = 0.031), cirrhosis (2.147; 1.421-3.242), extracorporeal membrane oxygenation support (1.811; 1.391-2.359), initial neurological dysfunction (1.448; 1.107-1.894; P = 0.007), pre-RRT mean arterial pressure (0.988; 0.981-0.995), inotropic equivalent (1.006; 1.001-1.012; P = 0.013), APACHE II scores (1.055; 1.037-1.073), and sepsis (1.939; 1.536-2.449) were independent predictors of the in-hospital mortality (All P<0.001 except otherwise stated). CONCLUSIONS The current study found a U-curve association between the timing of the RRT initiation after the ICU admission and patients' in-hospital mortalities, and alerts physicians of certain factors affecting the outcome after the RRT initiation.