Nutrition of Critically Ill Children With Acute Renal Failure

Objectives

This chapter will:

1.
Describe the importance of providing adequate nutrition in critically ill children with acute kidney injury (AKI).
2.
Provide an approach to assessment and monitoring of nutritional status in children with AKI and those treated with renal replacement therapy (RRT).
3.
Outline energy, protein, and other nutritional requirements in patients with AKI and those treated with RRT.

Malnutrition and protein energy wasting (PEW; muscle wasting and loss of fat) are common in children in the intensive care unit (ICU) because of many factors: hypercatabolism, stress-response substrate requirement; baseline nutrition status; ongoing growth needs (including brain growth in infants). Young children are at highest risk for PEW. AKI enhances the risk of PEW. Children with AKI tend to be among the most critically ill ICU patients. AKI and associated acidosis/uremia alters lipid, carbohydrate, and protein metabolism, promoting catabolism. With renal replacement therapy (RRT), nutritional losses worsen preexisting deficiencies. Finally, fluid overload often occurs in AKI, posing challenges to providing nutrition. Underfeeding is common in ICU children and even more prevalent in children with AKI, especially those receiving RRT. In AKI, the high risk of PEW must be appreciated. The goal should be to provide and enhance nutrition, rather than restrict. Although there are no nutrition trials in pediatric AKI, observational data demonstrate malnutrition is more common in AKI and contributes to poor outcome. An ongoing multinational pediatric ICU (PICU) study showed that ICUs with dedicated programs aimed at enteral nutrition advancement had lower infection rates, and adequate protein intake was related inversely to 60-day mortality. Thus, in recent years, the importance of adequate nutrition in children with AKI is appreciated increasingly as a basic principle of AKI management and a consideration for RRT initiation. For a detailed description of basic concepts of nutrition metabolism in AKI, the reader is referred to Section 14. This chapter presents issues regarding assessment, approach, and considerations specific to nutrition in children with AKI.

Assessment and Monitoring of Nutritional Status

Defining the nutritional status in critically ill children is an ongoing process. An international consensus group is working on defining and evaluating effects of malnutrition in children in the ICU. It is ideal to assess the nutritional status at admission, to elicit evidence of chronic malnutrition, and to anticipate critical illness nutritional issues. History may reveal past growth problems or nutrition deficits. Physical exam (hair, eyes, skin, mouth, extremities) may reveal specific signs of malnutrition or vitamin/mineral deficiencies. Height and weight (with minimal clothing; head circumference in children < 2 years old) should be measured in all patients. This may be challenging because of difficulties in moving patients (if bed scales are not available) or fluid overload (difficult to know patient's true weight).

When admission weight is uncertain, ideal body weight can be used for nutritional calculations. An effort should be made to calculate body mass index (BMI) at admission, which may reveal nutritional problems. These measures should be expressed as corrected age percentiles and z-scores. The 2006 World Health Organization (WHO) growth-for-age charts have been recommended in children younger than 2 years old and the Centers for Disease Control (CDC) charts in older children. Height, weight, and BMI z-score < 2 standard deviations from the mean are reasonable ways to screen for abnormal growth. Others have suggested height-for-age or weight-for-height < 10th percentile as a proxy for poor baseline nutritional status. Several nutrition scores have been published and may be considered. Measuring triceps skinfold thickness and mid upper arm circumference may be useful (expressed as z-scores). Weight (or triceps skinfold thickness and mid upper arm circumference) should be followed during admission, with the caveat in mind that edema may lead to underestimating weight loss. Biochemical parameters (e.g., albumin, prealbumin, visceral proteins) traditionally used to assess nutrition status often are altered by fluid shifts and should be interpreted cautiously. If there is suspicion for baseline chronic malnutrition, measuring trace elements or vitamin levels may be helpful to guide initial supplementation plans.

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