Profiling of peritoneal ultrafiltration.

The historical course of peritoneal dialysis can be charOVERVIEW OF ULTRAFILTRATION acterized by successive phases of development: the first PHYSIOLOGY phase after the introduction of continuous ambulatory It is important at the outset to review the balance of peritoneal dialysis (CAPD) was focused on establishing opposing forces governing peritoneal ultrafiltration in the therapy, addressing pressing technological needs in PD. These can be readily illustrated from the early work connectology and introduction of automation [1–8]. The of Mactier et al [17] represented in Figure 1. They evalusecond phase tackled controversial issues and ultimately ated ultrafiltration (UF) kinetics observed with the use led to the resolution of two contentious aspects: the vindiof 2.5% dextrose solution in CAPD patients with normal and high peritoneal transport patterns. The changes in cation of peritoneal dialysis as a long-term therapy with intraperitoneal volume are characterized by a biphasic patient outcomes equivalent to those of hemodialysis behavior: in the initial phase this is dominated by trans[9–12], and the proper determination of the relative imcapillary ultrafiltration, which is driven principally by the portance of small solute clearance by a definitive rancrystalloid osmotic gradient generated by glucose but is domized controlled trial [13] and cumulative observagoverned also by the relatively constant hydrostatic and tional explorations [reviewed in 13]. The present third oncotic pressure gradients (the so-called ‘Starling forces’) phase of the history of the therapy can be defined as [18]. As transcapillary ultrafiltration rate exceeds lymthat of focus on fluid balance and cardiovascular outphatic and tissue absorption, intraperitoneal volume incomes. This phase was heralded by the landmark work creases [17]. The decline in glucose concentration, howof the International Society of Peritoneal Dialysis ad hoc ever, occurs precipitously resulting in a decrease in the Committee of Ultrafiltration Management in Peritoneal transcapillary ultrafiltration rate. As long as transcapilDialysis [14, 15], which corrected the critical absence lary ultrafiltration exceeds lymphatic absorption, the of fluid management issues from dialysis management peritoneum is operating under a fluid transport disequiguidelines issued by various committees [16]. The work librium favoring positive net ultrafiltration. When the of the committee highlighted not only the importance transcapillary ultrafiltration rate declines to a value equal of the issue of fluid management, but also the limitations to the lymphatic flow rate, a state of equilibrium in fluid inherent in diagnostic evaluations of peritoneal ultrafiltransport obtains and no increase in intraperitoneal voltration [15]. One of the critical recommendations of the ume occurs. This is the point at which peak intraperitocommittee was the adoption of a variant of the peritoneal neal volume is reached. Peak UF volume is observed equilibration test (PET) utilizing a higher glucose conbefore osmotic equilibrium between serum and dialysate centration (4.25% dextrose/3.86% glucose) for the evaluis reached and occurs when the rate of net transcapillary ation of ultrafiltration failure [15]. This was based on the UF slows to equal that of lymphatic reabsorption [17]. recognition of the inadequacy of the standard 2.5/2.27% Thereafter, the rate of lymphatic reabsorption exceeds test to discriminate between true ultrafiltration failure that for net transcapillary UF, resulting in reduced intraand normal inter-individual variations. The aim of the peritoneal volume. present article is to pursue further the evaluation of The difference between the declining transcapillary the value of the standard PET in profiling peritoneal ultrafiltration rate and the constant lymphatic tissue absorption eventually leads to a new state of fluid transport ultrafiltration, and to offer a profiling model based on disequilibrium dominated by net fluid absorption and more extensive clinical data and mathematical modeling. negative net ultrafiltration. This characterizes the second and final phase of changes in intraperitoneal volume: a linear and steady decline [17, 18].