Salt and Water in PD: The Turkish Contribution

Abstract

It is now well accepted that fluid and salt balance play a critical role in the success of peritoneal dialysis (PD) therapy. The combination of fluid overload and hypertension can be a major factor in the development of cardiovascular disease, the leading cause of death in PD patients. Inadequate removal of fluid and sodium in PD is associated with increased mortality. There is growing evidence that PD patients are often volume expanded and have high blood pressure associated with left ventricular hypertrophy (LVH) and dysfunction. Improvement in fluid status may be achieved by rigorous salt restriction and optimization of peritoneal ultrafiltration. In this article and in light of relevant Turkish studies, evidence on the importance of fluid and sodium balance is summarized, and potential strategies for a better control of that balance in PD patients is outlined. IS THERE A NEED TO CHANGE THE INDICES OF PD ADEQUACY? Mortality in patients with end-stage renal disease is clearly higher than that in the general age-matched population, cardiovascular disease being the most frequent cause of death (1,2). The clinical outcome of PD patients is affected by many factors, including age, comorbid conditions such as cardiovascular disease and diabetes mellitus, nutritional status, inflammation, peritoneal membrane permeability, and dialysis adequacy. Adequacy of PD is traditionally assessed by small solute clearances, such as Kt/V urea or creatinine clearance. Although several studies have shown that insufficient small solute clearance in PD is associated with increased mortality and morbidity, the predictive power of both Kt/V urea and creatinine clearance on prognosis largely depends upon residual renal function (RRF), and not on the dialytic component of clearance (3‐6). Furthermore, no study has shown that a prospective increase in peritoneal clearance leads to improved outcomes. In the ADEMEX study, a large, prospective, randomized, controlled trial, increasing peritoneal solute clearance showed no beneficial effect on survival in PD patients, as a whole or in a subgroup of anuric patients (5). Although these findings should not lead to the assumption that the dose of PD is unimportant, they do indicate that we need to shift the focus of adequacy from only calculating small solute clearances to including other aspects of the care of PD patients, in particular fluid and sodium balance. There is no doubt that dialysis treatment should provide adequate solute and fluid removal in order to achieve good clinical outcome; however, until recently, the importance of fluid and sodium balance as a marker of adequate dialysis has largely been neglected. Also, in view of the finding in many studies that cardiovascular disease is the most common cause of death, accounting for nearly 50% of mortality (1,2), it is difficult to explain the influence of small solute clearance on cardiovascular disease. A possible explanation for this association may be the relationship of small solute clearance to fluid and sodium balance, which could have a direct effect on cardiovascular events. The constituents of small solute clearance provide clues for the main target for assessment of PD adequacy. The peritoneal clearance of small solutes is a product of their dialysate-to-plasma (D/P) ratio and drained dialysate volume. Since urea is nearly completely equilibrated between dialysate and plasma, its peritoneal clearance is determined mainly by drained dialysate volume. We examined the relationship between the constituents of Kt/V urea and mortality in 106 incident PD patients that were followed for 4 years. In the Cox model not containing RRF, peritoneal Kt/V urea was an independent predictor of mortality, following adjustments for age, comorbidity index, serum albumin, prealbumin, C-reactive protein, D/P creatinine, hypertensive status, and normalized protein nitrogen appearance. When the constituents of peritoneal Kt/V urea (D/P urea, drained di