Abstract
There is a sense that, during the 1990s, this topic was relatively neglected in the dialysis literature. Emphasis was on achievement of “adequate” dialysis as judged by measures of small solute clearance. Efforts to raise Kt/V and studies to prove its importance dominated dialysis meetings and publications and tended to draw attention away from other areas, such as volume management.
Now, in the aftermath of the ADEMEX and HEMO studies and their largely negative results, the pendulum has taken a welcome swing in the opposite direction. New studies on “adequacy” are increasingly uncommon, while attention to volume-related issues has greatly increased. All this is surely appropriate given the high rates of hypertension and cardiac disease in ESRD patients.
In peritoneal dialysis (PD), the renewed interest in volume management has been particularly striking and has been driven by a number of additional factors. First, the widespread rise in the popularity of cyclers over the past 10 – 15 years has appeared to increase the potential for fluid removal. Second, the increased availability of icodextrin has improved treatment options and has added a commercial impetus for studies on volume status. Third, the observation that patients with high peritoneal transport status had more fluid overload problems and worse outcomes on PD suggested this might all be very important. Finally, growth in interest in daily hemodialysis and its apparent advantages in volume management has challenged the PD community to look at how volume status can be better controlled in patients on PD.
The present era of interest in volume status in PD can be dated back to the publication of a Peritoneal Dialysis International (PDI) supplement, about a decade ago, dedicated to ISPD guidelines on volume management (1). The subsequent appearance of randomized controlled trials indicating that icodextrin could improve not only ultrafiltration but also volume status and echocardiographic indices added an encouraging positive note to the discussion. The importance of volume was further emphasized when a study from Turkey, and subsequently the multicenter EAPOS, showed an interesting correlation between net fluid removal and subsequent patient survival. Now there is a plethora of studies appearing that address volume-related issues in PD, and this trend is apparent from recent issues of PDI.
The present issue features a paper by Bavbek et al., from Turkey, examining the role of serum levels of natriuretic peptides in interpreting differences between volume control in CAPD and APD. Struijk, from Amsterdam, takes the opportunity to write an incisive commentary on the influence of PD modality on volume status, while another Dutch group, van den Kerkhof et al., looks carefully at the whole area of natriuretic peptides and dissects out their relative limitations as a useful clinical tool in dialysis patients. In the previous issue of PDI, Boudville and colleagues looked at the prevalence of hypertension in a contemporary PD population and its relationship with volume status and salt removal. An accompanying commentary by Davies put the observations into perspective. In that same issue, Woodrow et al. addressed the utility of bioimpedance measurements in assessing volume.
Despite all the studies, the topic of volume management remains full of controversies. The subject is perhaps more complex than that of adequacy and clearances and there has been little resolution of the major issues. It is worth highlighting some of the volume-related controversies that need to be worked out and that are being addressed in PDI:
What is the meaning of the association between greater fluid removal and better outcome? Does it imply that those who have more fluid removed have better volume control, or does it just mean they consume more salt and water? Is the associated better outcome a consequence of less volume overload, or is it just that greater fluid intake is a marker of better health?
Is there a real clinical problem with salt removal on APD compared to CAPD, and does it result in higher blood pressure and inferior outcomes for cycler patients? Are cyclers being overused, with volume control being sacrificed for convenience and lifestyle?
Icodextrin may raise ultrafiltration and decrease extracellular fluid volume, but does it improve control of blood pressure and reduce cardiac morbidity, and does it prolong life? Given its widespread utilization in clinical practice, will randomized studies large enough to answer such questions ever be done? Can the disadvantage of high transport status be ameliorated by the use of icodextrin?
How do we establish a given patient's optimal volume status? Is it still just trial and error, or can newer tests such as bioimpedance or measurement of natriuretic peptide levels or inferior vena cava diameters be useful adjuncts in clinical practices? More fundamentally, is it an advantage to reduce extracellular fluid volume and blood pressure to “normal” if, as a consequence, the patient loses residual renal function, the value of which has been emphasized so much. Similarly, is there a trade-off between optimizing volume status and limiting exposure to the toxicities of hypertonic glucose?
Is dietary salt restriction in PD important? Do diuretics have a role? What about low sodium PD solutions?
PDI will continue to contribute to these important debates. Contributions on these topics will be welcomed and, in general, research in this area is greatly needed.
Hiroshima, November 2007
This November, the Asian Chapter of the ISPD has its third meeting, which will take place in the city of Hiroshima in the south of Japan. The first two meetings of the Asian Chapter, in Hong Kong and Hyderabad respectively, were each a great success, even though the latter had to deal with the fallout of the great South Asian tsunami of 2004. As the site of the first atomic bomb used in warfare, Hiroshima has huge and poignant historical significance. In Japanese PD, it is the home of Dr. Hideki Kawanishi, who has contributed greatly to the understanding of encapsulating peritoneal sclerosis, particularly to its surgical management. PDI expects the meeting to be a great success and encourages its readers to attend.