Improved survival associated with acetate-free haemodialysis in elderly: a registry-based study

Acetate-free dialysis (AFD) improves haemodynamic stability during dialysis, compared with standard haemodialysis (HD) with a small amount of acetic acid. Using the national REIN registry, we classified 15 160 incident patients who started HD from 2008 to 2010 into three exposure categories according to the type of dialysate used in their dialysis unit: standard dialysate only (reference), both standard and AFD (mixed unit) or HCl dialysate only (100% HCl unit). Cox survival analysis was adjusted for 15 baseline comorbidities, laboratory data and haemodiafiltration (HDF). We took patient clustering within units into account, used age as the time scale and treated patient exposure to AFD and to HDF as time-dependent variables. Median age (interquartile range) was 70.5 years (58.1-78.8). Over a median follow-up of 1.8 years (1.2-2.6), 658 patients were dialysed in a 100% HCl unit, 3021 in a mixed unit and 11 481 were never exposed to AFD. The relation between AFD and mortality was not constant with age (Schoenfeld residuals test P = 0.01 for mixed group and P = 0.03 for 100%HCl group). Patients older than 70 years had a significantly lower mortality risk associated with AFD [hazard ratio (HR) = 0.79, 95% confidence interval (CI) = 0.67 to 0.94 for patients exposed in a 100% HCl unit; HR = 0.83, 95% CI = 0.74 to 0.94 for patients exposed in a mixed unit], but no association was found in younger patients. AFD was associated with improved survival independent of comorbidities and HDF in patients aged 70 years and older but not in patient younger than 70 years.