Relationship between dialysis adequacy addressed by Kt/V urea values and nutritional status in its effect on components of quality of life in incident peritoneal dialysis patients

Background: It is well known that the quality of life of patients with chronic kidney disease can be improved when dialysis is initiated. However, previous studies were conducted in retrospective designs and adhered to a standard target according to clinical guidelines. The study was a prospective design to investigate a longitudinal association between adequacy and nutritional indices and quality of life domains in a cohort of incident PD patients. Study design: A prospective 6-month observational study. Setting & Participants: Eighty incident PD participants who were treated in a hospital-facilitated PD center were enrolled. The period of enrollment was January 2009-June 2010; follow-up until December 2010. Predictors: PD adequacy indices; Kt/V urea, weekly Ccr (WCcr); nutritional index; nPCR, measured at one and 6 months after PD initiation. Outcomes & Measurements: SF-36 health survey questionnaires were used to measure quality of life. Outcomes measured the changes in the domains of SF-36 at 6month PD therapy. Results: Seventy-seven incident patients who initiated PD for 6 months completed the study. The mean age was 47.3 years old, and the male-to-female ratio was 38 : 39. A cutoff level of baseline peritoneal Kt/V urea of 1.2 was found to have the most influence on SF-36 domains. Patients with baseline peritoneal Kt/V urea < 1.2 had improvement in components of physical functioning and role limitation of physical functioning after a 6-month PD initiation. In contrast, patients with baseline peritoneal Kt/V urea ≥ 1.2 had remarkable improvement in components of general health, physical functioning, role limitation caused by physical problems and bodily pain. However, the trend of improvement disappeared in patients with baseline nPCR < 1.2. Baseline renal WCcr did not influence improvement in the SF-36 domains. Limitations: A small cohort in a short observation period. Conclusions: The levels of baseline peritoneal Kt/V urea had different influences on the components of quality of life after PD initiation. In addition, adequate nutrition played a definite role in the maintenance of quality of life in incident PD patients. Index words: peritoneal dialysis, quality of life, SF-36 Introduction The concept of health-related quality of life (HRQOL) in patients with chronic kidney disease (CKD), including end-stage renal disease (ESRD), has evolved since the inception of renal replacement therapy from simple survival to achieving a sense of well-being [1]. Patients with CKD usually tend to show a reduction in their quality of life (QoL) because of the several restrictions resulting from CKD treatment. Multiple factors, such as the presence of co-morbidities, can be related to the reduction of QoL. Interventions enhancing the clinical conditions and QoL of those patients are paramount, since the latter is directly associated with mortality in that population. The association between the reduction of QoL and preventable and controllable factors including diabetes [2], old age [3], inadequacy of dialysis, inflammation and poor nutrition is still uncertainly demonstrated in previous studies. In addition, studies have shown dialysis initiation improving QoL in ESRD patients [4-8]. However, the association between dialysis adequacy indices or nutritional parameters and QoL assessment is inconsistent. These results may be due to the small samples of patients, non-ESRD-specific assessments, inadequate observation periods, etc. There are several validated disease-specific HRQoL questionnaires that can be used for the dialysis cohort, such as the World Health Organization Quality of Life Survey (WHOQOL), Short Form Health Survey (SF-36), the Kidney Disease Quality of Life (kDQOL), and the Choices Health Experiences Questionnaire (CHEQ). Peritoneal dialysis (PD) patients who had Kt/V urea above 2.0 have been demonstrated to have higher total SF-36 scores [6], although some argue there is a poor correlation between Kt/V urea and SF-36 scores [8]. There are only two validated native language editions of questionnaires in Taiwan: the WHOQOL and the SF-36. In Taiwan, SF-36 questionnaires have been reported to be a validated tool in a multi-center study comparing the QoL between PD and hemodialysis patients [9]. In this study, we used the SF-36 to assess QoL in an incident cohort of PD patients. The purpose of the study was to investigate which components of the SF-36 could be improved after PD initiation. In addition, the influences of adequacy indices of PD and nutritional status upon the components of SF-36 were explored. Materials and Methods Incident ESRD patients who consulted the PD institution at a medical center in southern Taiwan between January 2009 and June 2010 were enrolled into this prospective study. The inclusion criteria for the incident PD patients included: having received regular PD therapy for at least three months, aged more than 17 years, able to express themselves and having no history of psychiatric disease, and clinically stable with no evidence of chronic or acute infections, inflammatory disorders, malignancy, or anti-inflammatory drug use three months prior to enrollment. The exclusion criteria were as follows: (1) less than 17 years of age; (2) unable to complete the questionnaires by themselves; (3) major clinical events requiring admission; and (4) discontinuation of PD for the following reasons: kidney transplantation, technique failure, death, transfer to hemodialysis, and loss to followup. According to the study protocol, all patients completed at least six months of consecutive PD therapy; A total of 77 of 80 clinically stable patients (38 male and 39 female) were finally eligible. The mean age was 47.3 years. All patients were dialyzed using commercially available dialysate (pH 5.2; Dianeal PD solution; Baxter, Singapore) containing 40mmol/L lactate. Forty-five patients received CAPD, four exchanges every day. Thirty-two patients received automated peritoneal dialysis (APD) therapy. QoL was measured using the Chinese-language version of the 36-item Short Form Health Survey Questionnaire (SF-36, Taiwan Standard Version 1.0), a generic selfreport QoL instrument. The SF-36 consists of 36 items, which are assigned to 8 domains, including general health, physical functioning, role limitation due to physical problems, bodily pain, mental health, social functioning, role limitation due to emotional problems, and vitality. The first four domains constitute the physical component scale, and the second four, the mental component scale. Higher scores suggest better QoL. All patients were asked to complete the SF-36 questionnaire at baseline and six months after PD initiation. Standard P.E.T. was performed in the first month and the 6 th month after PD initiation. The clinical characteristics of all patients, including demographic and biochemical data, the PD adequacy indices (renal and peritoneal Kt/V urea, Ccr), and nutritional indices [serum albumin, normalized protein catabolic rate (nPCR)] were collected at baseline and at the 6 th month for statistical analysis. The protocol for the present study was approved by the Committee on Human Research at Kaohsiung Chang Gung Memorial Hospital (CMRPG880091) and conducted in accordance with the Declaration of Helsinki. All participants signed an informed consent form to obtain approval to take part in the study. Statistical analysis Using the general linear model, we tried out and determined an applicable Kt/V value to investigate the effect of Kt/V on QoL (Table 1). Based on the selected Kt/V value, demographic data including age and gender, clinical data including peritoneal urea Kt/V, residual renal urea Kt/V, total Kt/V, peritoneal weekly Ccr, residual renal weekly Ccr, total weekly Ccr, hs-CRP, albumin, GPT, Hb, and nPCR, and the eight multi-item domains of the SF36 were all recorded and grouped, and compared with the Mann-Whitney test, Chi-Square test or likelihood ratio test. Thus, age, peritoneal Kt/V, residual renal WCcr and nPCR were regarded as independent variables to explore the differences in the influence of the SF-36 scores between one month and six months after PD therapy initiation. Statistical analyses were performed using the IBM SPSS Statistics 19 (SPSS Inc. Chicago, IL) program.