In our study, the cut-off for the definition of an ‘older’ individual was 70 years of age. All incident patients aged 70 or older who started on PD between 1 January 2009 and 31 December 2018 at Renji Hospital, Shanghai Jiao Tong University School of Medicine, China, were screened for eligibility. Patients had history of maintenance HD/transplantation, withdrew from PD within 3 months or with incomplete data were excluded from the study. All enrolled patients were dialyzed using lactate-buffered glucose-based PD solutions (Dianeal®, Baxter) with twin-bag system. Patients and their caregivers had received standard training after catheterization by PD dedicated nurses 16. The study was approved by the Human Research Ethics Committee of Renji Hospital, Shanghai Jiao Tong University School of Medicine. All individual information was securely protected and was made available to only the investigators.
Demographic and laboratory data
The demographic characteristics collected at baseline included age, gender, height, weight, underlying cause of ESRD and comorbid condition status such as diabetes mellitus (DM) and cardiovascular disease (CVD). Hypertension and diabetes were defined either as a comorbid disease or as the etiology of ESRD. CVD was defined as a previous history of any following condition: acute coronary syndrome, heart failure, cerebral infarction or hemorrhage, coronary artery atherosclerosis confirmed by percutaneous coronary intervention (PCI) or coronary artery bypass grafting (CABG) therapy. The Charlson comorbidity index was adopted to reflect the burden of comorbid conditions. Body mass index (BMI) was calculated as the weight (kg) divided by the square of height in meters (BMI =weight [kg]/ height [m2]).
Baseline laboratory parameters included hemoglobin, serum albumin, creatinine, urea nitrogen, uric acid, sodium, potassium, corrected calcium, phosphate, intact parathyroid hormone (iPTH), total cholesterol, total triglycerides, high-sensitivity C reaction protein (hs-CRP), estimated glomerular filtration rate (eGFR) (mL/min/m2) and fasting blood glucose were collected. The corrected calcium (mmo1/L) = total calcium (mmol/L) + (40- albumin) × 0.025 (mmol/L).
Small solute clearance and peritoneal transport characteristics
All patients were evaluated small solute clearance and performed a standard peritoneal equilibration test (PET) 1-3 months after PD initiation. Small solute clearance was assessed by 24-h dialysate and urine collection, with the calculation of total weekly Kt/V and weekly CrCl normalized to 1.73m2 body surface area 17. Residual renal function (RRF) was calculated as an average of 24-h urine urea and creatinine clearance 18. Normalized protein catabolic rate (nPCR) was calculated by the methods described by Randerson, Chapman, and Farrell and normalized to standard body weight (total body water/0.58) 19.
Patient follow up
The enrolled patients were divided into assisted PD group (PD exchanges performed by a family member or a domestic helper) and self-care PD group according to the independence of bag exchange, and prospectively followed up until death, transfer to permanent hemodialysis, recovery of renal function, transfer to other centers, lost to follow-up or to the end of study (December 31st, 2019). All deaths, switches to HD and peritonitis episodes during the study period were carefully tracked and recorded. Detailed causes of death, switches to HD and outcome of peritonitis during PD were also collected. Causes of death were grouped in broad categories as follows: cardiovascular, including cardiac, cerebrovascular, peripheral vascular and sudden death; infection, including peritonitis and non-peritonitis infections; cancer; gastrointestinal hemorrhage; other and unknown causes. Causes of switch to HD were grouped into peritonitis; catheter complications; inadequate dialysis and other causes. Peritonitis was diagnosed and managed in accordance with guidelines of the International Society for Peritoneal Dialysis 20, and peritonitis rate was calculated as number of peritonitis episodes per patient-year at risk.
Outcome measures in our study included patient survival, peritonitis-free survival and technique survival. In patient and peritonitis-free survival analysis, the endpoint was death and first episode of peritonitis, respectively. In technique survival analysis, the endpoint was permanent transfer from PD to HD. For both patient and peritonitis-free survival analysis, the censored events were transfer to permanent hemodialysis, recovery of renal function, loss to follow-up, transfer to other dialysis centers, or to the end of study (December 31st, 2019). In technique survival analysis, the endpoint was permanent transfer from PD to HD, and death was regarded as censored event.
The Kolmogorov–Smirnov test was used to measure data normality. Parametric data were presented as mean ± standard deviation. Nonparametric data were described by the median value (first and third quartile). Categorical variables were presented by frequencies and percentages and were compared using chi-square tests. Normally distributed continuous variables and abnormally distributed continuous variables were compared using the independent sample t-tests and Mann-Whitney test, respectively. Kaplan-Meier and log-rank test methods were used to estimate and compare survival curves for each event of interest (death, peritonitis and transfer to HD) by comparing assisted PD group with self-care PD group. Considering the presence of competing events in this study, for multivariate analysis, risk factors for all-cause mortality, peritonitis and technique failure were evaluated by both cause-specific hazards and subdistribution hazards models 21. When the event of interest was peritonitis, transfer to HD, renal transplantation, death and transfer to other centers were coded as competing events only when occurring before the first peritoneal infection. When the event of interest was death, the competing events included transfer to HD, renal transplantation and transfer to other centers. When the event of interest was technique failure, the competing events included death, renal transplantation and transfer to other centers.
Data analysis was carried out using the SPSS software package (version 22.0: SPSS, Chicago, IL, USA) and R 3.6.1 (R Foundation for Statistical Computing, Vienna, Austria; the ‘cmprsk’ library was used to fit the Fine and Gray regression models). All probabilities were two-tailed, and a p< 0.05 was considered statistically significant.