Anthropometric Prediction of Total Body Water in Children Who Are on Pediatric Peritoneal Dialysis

Abstract

Accurate estimation of total body water (TBW) is a critical component of dialysis prescription in peritoneal dialysis (PD).Gold-standard isotope dilution techniques are laborious and costly; therefore, anthropometric prediction equations that are based on height and weight are commonly used to estimate TBW. Equations have been established in healthy populations, but their validity is unclear in children who undergo PD, in whom altered states of hydration and other confounding alterations in normal physiology, particularly retarded growth and pubertal delay, may exist. TBW was measured by heavy water (H 2 O T he accurate determination of total body water (TBW) is a critical component of the dialysis prescription and measurement of the delivered dialysis dose. Urea kinetic modeling is a key underpinning to dialysis prescription. An estimate of the urea distribution space (V) is required to calculate normalized urea clearance, i.e., Kt/V (1) for patients who are on peritoneal dialysis (PD) using these models. The urea distribution space, V, is assumed to be the same as TBW. Accurate measurement of TBW requires sophisticated measurement techniques, such as isotope dilution measurements (2), which are costly and time-consuming and, hence, not suitable for routine clinical practice. TBW therefore usually is estimated from anthropometric measurements.The Kidney Disease Outcomes Quality Initiative PD adequacy guidelines recommend the use of the formulas of Mellits and Cheek (1) to estimate V in children who are on PD. These formulas are based on heavy water dilution studies that were performed in healthy children and estimate TBW using a child's height, weight, and gender (3). Recently, isotope dilution-derived TBW data that were obtained in healthy neonates and infants were added to the original data set of Mellits and Cheek, and a new set of anthropometric prediction equations were proposed (4). In these equations, a new anthropometric parameter height times weight (HtWt) that correlates linearly with TBW when both values are log-transformed was introduced (4). Estimates from the newer formulas are somewhat more accurate for infants but are still based on data that were obtained in healthy children.In the PD population, disorders of growth and body composition are common and superimposed on large variations of fluid status. Because direct measures of TBW in children who are on PD using the "gold standard" assays involving heavy water have not been reported in large cohorts of children (5,6), it is unknown whether the anthropometric prediction equations that have been established in healthy children hold true in this population. Hence, the objectives of this study were to (1) measure TBW in children incident to maintenance PD using heavy water, (2) develop and validate population-specific (i.e., children on PD) formulas to estimate TBW on the basis of

Is body composition important for paediatricians?: Figure 1

“…For calculation of dialysis dosages, anthropometric predictive equations developed in healthy children overestimate body water in dialysis patients, and new equations derived from patients receiving chronic peritoneal dialysis have been derived 49. However, these equations still have a standard error of 2.2 litres, and in a study of 14 paediatric dialysis patients, measurements of lean mass by DXA allowed estimation of body water with a substantially smaller error of 1 litre 47.…”

No difference in meeting hemoglobin and albumin targets for dialyzed children with urologic disorders

“…For PD patients, total Kt/V was calculated as the sum of renal Kt/V and dialysis Kt/V −total (renal+dialysis)kt/V) [14]. Total body water (V) was calculated using the sex-specific formulas created by Morgenstern et al specifically for patients who are on peritoneal dialysis [15]. …”

Serum cystatin C for estimation of residual renal function in children on peritoneal dialysis

“…The C cr and C urea were adjusted to a standardized body surface area of 1.73 m 2 . The urea generation and its distribution volume were assessed using traditional urea kinetic modeling [24,25]. All parameters were calculated with the program available at www.pedpd.org, the website of the International Pediatric PD Network (IPPN).…”