Small solute clearance measured by Kt/V urea is known to be one of the major determinants of dialysis adequacy. A growing body of evidence has suggested that a strong link exists between Kt/V urea values and mortality rates in dialysis populations . Therefore, to reduce the risk of mortality and improve dialysis adequacy, the total (renal + peritoneal) Kt/V urea value should not be less than 1.7 for small solute removal, according to the guidelines of the Kidney Disease Outcomes Quality Initiative (KDOQI) and the International Society for Peritoneal Dialysis (ISPD) [11, 12]. To reach this target, however, patients might experience adverse effects, including hernias (from the increased intra-abdominal pressure due to large volumes of dialysis solution), weight gain, and other metabolic consequences due to increased exposure to glucose. Furthermore, the increased amount of time needed to perform the exchanges is less acceptable to patients. These factors might not only adversely affect the willingness of the patients to continue PD therapy but also affect the QoL in incident PD patients. However, one study reported that a lower Kt/V urea target was associated with a similar survival rate , leading us to consider what the impact of a lower Kt/V urea target would be on QoL. In our study, we carefully stratified our patients on the basis of peritoneal Kt/V urea values into 2 groups. Peritoneal Kt/V urea is the major component of total weekly Kt/V urea and is the critical component targeted in dialysis regimens. We found that patients with a peritoneal Kt/V urea value of >1.2 experienced significant improvement in the QoL, especially in the domains of general health, physical function, and role limitation due to physical problems, at 6 months after the initiation of PD. Our results suggest that PD on its own is highly beneficial in improving the QoL in patients whose peritoneal Kt/V urea value is above 1.2. This result implies that some domains of the QoL could be improved after 6 months of PD therapy with a lower peritoneal Kt/V urea target. However, the influence of a lower peritoneal Kt/V urea value on long-term QoL and patient survival needs to be further investigated. Our study also suggests that it might not be necessary to pursue a higher adequacy target at the expense of QoL in the early phase of PD initiation. By not pursuing a higher adequacy target, the early discontinuation of incident PD patients observed occasionally can be avoided.
The nPCR value, also called protein equivalent of nitrogen appearance (PNA), can be used to assess dietary protein intake in patients who are in a steady state. It has also been adopted as a reference value to adjust dialysis prescription. When poor nutrition (e.g., nPCR < 0.8 g·kg-1·day-1) or inadequate dialysis (e.g., Kt/V urea < 1.2) is apparent, the dialysis prescription has to be adjusted to meet the clinical situation. Moreover, to ascertain whether a significant change has occurred may require several months of nPCR and Kt/V urea level monitoring. A previous study has demonstrated that mortality rates increased in dialysis patients with nPCR values of less than 0.8 g·kg-1·day-1 or greater than 1.4 g·kg-1·day-1. Among patients with nPCR levels between 0.8 g·kg-1·day-1 and 1.2 g·kg-1·day-1, an increase or decrease in protein intake during the first 6 months was associated with an increase or decrease in the survival rate over the subsequent 18 months, respectively. Thus, reduced survival is associated with an initially low nPCR and decreased protein intake over time. In the present study, patients with baseline nPCR values of >1.2 g·kg-1·day-1 had higher renal Kt/V urea values and higher weekly Ccr values than those with nPCR values of <1.2 g·kg-1·day-1. Patients with nPCR values greater than 1.2 g·kg-1·day-1 showed improvement in SF-36 domain scores after 6 months of PD therapy. In contrast, patients with nPCR values of <1.2 g·kg-1·day-1 showed a decrease in SF-36 domain scores after 6 months of PD therapy. The exact mechanism by which residual renal function improves the QoL in subjects with nPCR values of >1.2 g·kg-1·day-1 needs to be further investigated. However, this finding implicates nutritional status as key factor in QoL improvement with PD initiation. Therefore, it is essential to devise a strategy to increase the nutritional status primarily in the early phase of PD commencement.
In the past few years, some investigators have focused on the reasons for the early discontinuation PD therapy by patients. The NECOSAD study demonstrated that the psychosocial effect of PD therapy was a one of the major reasons why patients discontinued therapy in the first 3 months . Another study from a single PD center also showed that psychosocial effects were a major cause of early discontinuation of therapy in the first 6 months of PD therapy . However, one study has shown that the measures of social relationships and physical health of PD patients did not significantly change during the early and late phases of treatment . Furthermore, it has been found in one study that emotional defensiveness affects the physical and mental components of HRQoL in patients undergoing dialysis . In that study, the incident PD patients needed an adjustment period to adapt to their uncertain psychological status; the complex, time-consuming PD exchange procedure affected their response to PD therapy. This finding suggests that psychological effects must not be ignored in the management of patients undergoing dialysis. Our study clearly showed that PD could improve the QoL, as measured by the SF-36 instrument, after 6 months of therapy. However, we found that a lower peritoneal Kt/V urea value further contributed to a remarkable improvement in the QoL. We assume that a more satisfactory PD prescription might reduce the psychosocial burden on incident PD patients, even though it would attain a lower adequacy index. This approach did not sacrifice the QoL in incident PD patients, as per our results.