Nutritional Management of Children Undergoing Peritoneal Dialysis

Nutritional management is a key component of the care of children treated with peritoneal dialysis (PD). This includes regular assessment of nutritional status as well as development and implementation of a dietary prescription. Optimal nutritional management requires collaboration among the child, the caregivers, a renal dietitian, and other members of the multidisciplinary pediatric nephrology team. The goals are to achieve normal growth, development, and body composition and to avoid the complications associated with malnutrition and electrolyte disturbances. Although growth failure is recognized as one of the distinctive features of children with chronic kidney disease (CKD), it is not inevitable. Adequate growth is achievable and is a good indication of adequate nutrition over the long term. Because height has an important impact on self-esteem and perceived quality of life, normal final adult height should be the goal for all children.

It is useful to consider both the patterns and drivers of growth in healthy children when approaching children treated to PD. The infancy phase of growth is dominated by nutrition, the childhood phase by growth hormone, and the pubertal phase by sex hormones. Children with CKD may have disturbances in all of these factors, including a delay in the transition from the infancy phase to the childhood phase (which results in a slower than normal growth velocity). In infancy, poor caloric intake caused by anorexia is the main contributor to growth impairment, but energy intakes for older children with CKD are usually normal relative to size. A much larger proportion of the daily energy requirement is devoted to growth in infants than in older children. Poor appetite may result from a combination of factors, including a thirst for water rather than food, administration of unpleasant medications, disordered gastric motility, and dysregulation of appetite-regulating cytokines and hormones.

It is important to note that not all abnormalities in growth and body composition in children treated with PD are related to inadequate nutrition. Other factors may also play a role in the wasting—or “cachexia”—that may occur in CKD, including systemic inflammation, endocrine perturbations, and abnormal neuropeptide signaling.

Assessment of Growth and Nutritional Status

Growth Parameters

As for healthy children, the recommended frequency for assessment of growth and nutritional status in CKD depends on the age of the child ( Table 76.1 ) and should be individualized according to clinical status. On average, growth assessment should be done four times as often in children treated with PD compared with healthy children. Basic measurements include weight for age, stature for age (recumbent length in children younger than 24 months, standing height for those older), and head circumference (in children 3 years and younger). It is recommended that the World Health Organization (WHO) growth charts be used as a reference from birth to 2 years because these standards represent ideal growth (which should be the goal for children with CKD). After age 2 years, there is minimal difference between the U.S. Centers for Disease Control and Prevention (CDC) reference curves and WHO growth standards. Calculation of body mass index (BMI) is useful to see if the child's weight for height places them in an at-risk category (underweight, overweight, or obese). When plotting BMI relative to age in a child with growth or maturational delay, this may result in inappropriate underestimation of their BMI compared with peers of similar height and developmental age. This problem can be avoided by expressing BMI relative to height age rather than chronologic age in children with CKD. Height age is the age at which the child's height would be at the 50th percentile. Although the primary focus of nutritional assessment in children on PD has typically been to identify undernutrition, it is important to note that obesity is increasing in frequency.

Table 76.1

Recommended Nutritional Assessment for Children with Stages 2 to 5D Chronic Kidney Disease

Measure	Minimum Frequency, by Age
Measure	0 to < 1 Year	1–3 Years	> 3 Years
Height or length for age percentile/SDS	Every 2 weeks to 1 month	Every 1 month	Every 1–3 months
Height or length velocity for age percentile/SDS	Every 2 weeks to 1 month	Every 1–2 months	Every 6 months
Estimated dry weight and weight for age percentile/SDS	Every 1 week to 1 month	Every 2 weeks to 1 month	Every 1–3 months
BMI for height age percentile/SDS	Every 2 weeks to 1 month	Every 1 month	Every 1–3 months
Head circumference for age percentile/SDS	Every 2 weeks to 1 month	Every 1–2 months	Every 1–3 months
Dietary intake	Every 2 weeks to 2 months	Every 1–3 months	Every 3–4 months

BMI , Body mass index; SDS , standard deviation score.

Weight assessment can be challenging in children on PD because of changing volume status. “Dry weight” (i.e., euvolemic weight) should be estimated based on blood pressure, presence of edema, response to ultrafiltration, and serum albumin. The volume of the daytime dialysate dwell must be subtracted from the measured weight.

Dietary Intake

Information about dietary intake provides useful indices of nutrient quantity and quality. It is important to estimate total daily intake of calories, macronutrients (carbohydrate, protein, and fat), vitamins, and minerals. The most clinically feasible methods of determining usual dietary intake are the prospective 3-day dietary diary and the retrospective 24-hour recall (done three times, 1 weekend day + 2 weekdays). The retrospective 24-hour recall, although limited by its inability to capture the day-to-day variability in intake, may be more suitable for adolescents, in whom underreporting is common with 3-day dietary histories.

A skilled dietitian will also consider a number of other factors in a comprehensive dietary history, including any dietary or fluid restrictions and compliance with these restrictions, appetite changes affecting intake, feeding history, and relevant clinical information. Feeding history includes information on who is involved with preparation and offering of food (supervised or unsupervised child vs. primarily from caregivers), how the food is prepared and delivered (e.g., enteral feeding devices, oral), frequency and timing of feeds (daytime or nighttime), and any oral aversions, swallowing difficulties, reflux, or vomiting.

Other important clinical information includes urinary output, usual body weight (and trends), food security (capacity of family to afford feeds consistently), level of physical activity, and current dialysis prescription (may impact nutritional requirements based on glucose concentration of dialysis fluids and intake, e.g., early satiety because of daytime dwell volumes).

Physical Examination

A thorough physical examination is an important part of the nutritional assessment. The hydration status, presence or absence of edema, and blood pressure can provide useful guides as to the true dry weight. Signs of nutritional deficiency should be noted. The skin may be dry with excess flaking and uneven pigmentation, and the hair may be brittle, dry, and easily shed. Angular cheilosis and stomatitis, hepatomegaly, and certain neurologic abnormalities may each point to vitamin deficiencies. Genu deformities of the limbs, thickened wrists, costochondral beading (the rachitic rosary), and thickening of the wrists may point to vitamin D–deficient rickets.

Adequacy of Dialysis

It is important to remember that inadequate dialysis may result in poor appetite, nausea, deranged biochemical indices, hypertension, and edema. Dialysate clearances of urea normalized to total body water (Kt/V _urea ) and the creatinine (CCr) normalized to body surface are measures of dialysis adequacy. Target Kt/V is at least 2.1 to 2.2 per week. Studies in children treated with hemodialysis (HD) showed that catch-up growth was achievable when higher than standard doses of HD were used (Kt/V > 2.0 per treatment). It is not known whether enhanced PD clearance would also result in better growth; achieving clearances much higher than recommended would be very difficult with PD because of limitations in feasible hours of treatment and fill volumes.

Dietary Prescription

The international Pediatric Renal Nutrition Task Force recently coined the novel term “Suggested Dietary Intake” (SDI). The SDI recognizes that different countries and organizations around the world recommend slightly different nutritional intakes for healthy children and that none of these is clearly superior to any other. Therefore, the SDI includes a range of values.

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