Fluid and electrolyte imbalances in children with chronic renal failure

Alteration of the maximal renal water excretion capacity with kidney function and age in human

PURPOSE

The kidney's capability to concentrate and dilute urine is crucial to maintaining body fluid compartments and plasma osmolality. Advanced age and chronic kidney disease (CKD) result in decreased maximal urine concentration. Less is known regarding urine dilution ability. The primary purpose of this study was to determine the relationship between maximal renal water excretion and renal function, age, and gender in humans.

METHODS

This monocentric retrospective study includes patients referred to the Department of Clinical Physiology in Toulouse University Hospital to measure the glomerular filtration rate (mGFR) between April 2013 and February 2018. mGFR was assessed using inulin renal clearance and required ample hydration. We quantified the effects of age, gender and mGFR have on water excretion ability, which was assessed by minimal urinary osmolality (minUosm) and maximal free water clearance (maxCH2O).

RESULTS

666 patients were included (mean age 51 ± 14 years, 53% female). Mean mGFR was 82 ± 25 mL/min/1.73m2. MinUosm after hydration was higher in patients with renal insufficiency while maxCH2O was markedly lower. Age was also, with a weaker effect, associated with decreased in water excretion, independently of mGFR. MaxCH2O clearance was similar in both genders, whereas minUosm was lower in women, possibly resulting from a lower osmotic load.

DISCUSSION

This study shows a decrease in maximal urinary dilution capacity and free water clearance with CKD and age, without gender difference. These alterations are mild but must be considered when a significant water intake is required or in the case of hyponatremia.

Fluid management in hospitalized pediatric patients

The proper use of intravenous fluids has likely been responsible for saving more lives than any other group of substances. Proper use includes prescribing an appropriate electrolyte and carbohydrate solution, at a calculated rate or volume, for the right child, at the right time. Forming intravenous fluid plans for hospitalized children requires an understanding of water and electrolyte physiology in healthy children and how different pathology deviates from the norm. This review highlights fluid management in several disease types, including liver disease, diabetic ketoacidosis, syndrome of inappropriate antidiuretic hormone, diabetes insipidus, kidney disease, and intestinal failure as well as in those with nonphysiologic fluid losses. For each disease, the review discusses specific considerations, evaluations, and management strategies to consider when customizing intravenous fluid plans. Ultimately, all hospitalized children should receive an individualized fluid plan with recurrent evaluations and fluid modifications to provide optimal care.

Optimizing Enteral Nutrition for Growth in Pediatric Chronic Kidney Disease (CKD)

Growth in pediatric Chronic Kidney Disease is important for long-term outcomes including final adult height and cognitive function. However, there are many barriers for children with chronic kidney disease to achieve adequate nutritional intake to optimize growth. This review highlights these unique concerns, including route of nutrition, dialysis contributions and biochemical indices. Fitting the enteral feeding to the patients' needs involves choosing an appropriate product or products, limiting harmful nutrients in excess, notably aluminum, and altering for electrolyte and micronutrient needs. Unique adjustments to the enteral regimen include accommodating volume needs, optimizing macronutrient ratios, specific electrolyte adjustments, the blending of products together, and adjustments made to consider patient and family psychosocial needs. When a holistic approach to medical nutrition therapy is applied, taking the above factors into consideration, adequate intake for growth of the child with CKD is achievable.

Nutrition in infants and very young children with chronic kidney disease

Provision of adequate nutrition is a cornerstone of the management of infants and very young children with chronic kidney disease (CKD). Very young children with CKD frequently have poor spontaneous nutritional intake. Because growth depends strongly on nutrition during early childhood, growth in very young children with CKD is often suboptimal. In this review we will consider the mechanisms and manifestations of inadequate nutritional status in very young children with CKD, mechanisms mediating inadequate nutritional intake, and the optimal nutritional management of this special population. In addition, we suggest an approach to the assessment of nutritional status, including the use of body mass index in infants. Five major nutritional components are considered: energy, macronutrients, fluids and electrolytes, micronutrients, and calcium/phosphorus/vitamin D. The use of adjunctive therapies, including appetite stimulants, treatment of gastroesophageal reflux and gastric dysmotility, enhanced dialytic clearance, and growth hormone, is also briefly discussed.

Optimal care of the pediatric end-stage renal disease patient on dialysis

This manuscript is an effort on behalf of the American Society of Pediatric Nephrology to provide recommendations designed to optimize the clinical care of pediatric patients with end-stage renal disease (ESRD). Although many of the recommendations are evidenced-based with the supporting data being derived from a variety of sources, including patient registries, others are opinion-based and derived from the combined clinical experience of the authors. In all cases, it is recommended that the decision to initiate dialysis should be made only after an assessment of a combination of biochemical and clinical characteristics. Irrespective of the choice of dialysis modality (hemodialysis v peritoneal dialysis), dialysis efficacy should be measured regularly, and the dialysis prescription should be designed to achieve target clearances. Attention to dialysis adequacy, control of osteodystrophy, nutrition, and correction of anemia is mandatory, because all may influence patient outcome in terms of growth, cognitive development, and school performance. Finally, the availability of a multidisciplinary team of pediatric specialists is desirable to provide all facets of pediatric ESRD care, including renal transplantation, in an optimal manner. Future clinical research efforts intended to address topics such as dialysis adequacy, anemia management, and growth should be encouraged.

Sodium or chloride deficiency lowers muscle intracellular pH in growing rats

Sodium deficiency and chloride deficiency are associated with a contracted extracellular (ECF) volume and impaired growth in young children and growing rats. In cell culture, lowering sodium in the medium reduces growth factor-stimulated Na+/H+ exchange activity, intracellular pH (pHi), and DNA synthesis. We studied the effect of chronic sodium deficiency and chloride deficiency upon growth, extracellular acid base status, and muscle pHi in young rats. We fed growing rats for 21 days either a control diet, or one deficient in sodium (0.005%), chloride (0.005%), or calories. Muscle pHi was measured using 31phosphorus nuclear magnetic resonance spectroscopy. Rats fed either the sodium-deficient or chloride-deficient diet developed ECF volume contraction and hyponatremia; growth in length and weight was impaired. Muscle pHi was decreased (pHi = 7.074 +/- 0.006, 7.078 +/- 0.006 vs. control 7.100 +/- 0.002; P < 0.02). In calorie-restricted rats, growth was impaired but pHi was not affected (pHi 7.103 +/- 0.008). Metabolic alkalosis developed in the chloride-deficient group; acid base status was not affected in the sodium-deficient group. Despite differences in ECF acid base status, both groups had a low muscle pHi. We speculate that the low muscle pHi was a result of the ECF volume contraction and hyponatremia; low muscle pHi may contribute to retarded cell growth.

Plasma renin activity as a marker for growth failure due to sodium deficiency in young rats

We evaluated the effect of feeding diets of varying sodium content on growth and plasma renin activity (PRA) in young rats. In the first study, four groups of rats were offered 10 g/100 g body weight per day of diets containing either 0.005%, 0.015%, 0.03%, or 0.3% sodium; weight gain per day of each rat was followed for 10-14 days and PRA was then measured. A control group was fed a sodium-replete tryptophan-deficient diet which caused protein calorie malnutrition and inhibited growth. Weight gain (g/day) among the rats on the sodium-deficient diets varied directly (r = 0.81, P < 0.001) and PRA inversely (r = -0.82, P < 0.001) with dietary sodium content. PRA varied inversely with weight gain (r = -0.84, P < 0.001). Insulin-like growth factor-1 (IGF-1), which is depressed in calorie-deficient growth failure, was depressed in all the rats on the low-sodium intakes relative to ad libitum-fed controls, but did not vary in relation to dietary sodium or weight gain within those groups. In rats fed the tryptophan-deficient diet, both IGF-1 and weight gain were severely depressed; PRA was normal. In the second study, rats in each of two groups were pair fed, the diet containing either 0.03% or 0.3% sodium matched to rats fed the 0.005% sodium diet; weight gain was followed for 28 days. Both length and weight gain were retarded; PRA again varied inversely with dietary sodium content and with weight gain.(ABSTRACT TRUNCATED AT 250 WORDS)

Growth failure in renal disease

Children with congenital CRF lose height potential mainly during two distinct growth periods; infancy and puberty. The onset of puberty is late, the pubertal growth spurt starts from a very low rate of growth velocity, and peak height velocity is lower than normal although the absolute increment of height velocity is comparable to the increment in normal children. Furthermore, the duration of pubertal growth spurt is reduced in CRF. During infancy and early childhood, malnutrition, electrolyte disturbances and metabolic acidosis are the main contributing factors for reduced growth, whereas hormonal disturbances are responsible for growth impairment during puberty. There is evidence for resistance to growth hormone in CRF, which starts in early childhood and persists until the end of puberty. Growth hormone secretion is normal in CRF, but GH half-life is prolonged. The binding activity of the stable growth hormone binding protein is reduced, which points to a low receptor expression in the liver. Hepatic IGF-I production is diminished. However, the serum concentration of IGF binding proteins (IGFBP) is increased due to reduced renal filtration of low molecular weight subunits of IGFBP. Mainly, the accumulation of IGFBP-3 leads to increased IGF-binding capacity of the uraemic serum. Both, reduced IGF-I production and increased binding of IGF to IGFBP-3 result in decreased IGF bioactivity. During infancy, loss of growth potential can be prevented by adequate nutrition. Later in life, catch-up growth cannot be induced by nutritional intervention or dialysis. Renal transplantation allows catch-up growth in only a small percentage of patients. Treatment with one IU rhGH/kg/week improves growth velocity and growth in all stages of renal disease. The mean increment of height in prepubertal children is +1.5 SDS within two treatment years. The effect of rhGH during puberty as well as the effect on final height remain to be determined.

The effect of sodium repletion on growth and protein turnover in sodium-depleted rats

This study examines the consequences of sodium chloride supplementation to young rats previously made salt deficient by feeding them a sodium-deficient, chloride-replete diet. Salt-deficient rats received the test diet and distilled water for 10 days. As in our previous studies, rats cared for in this manner grew more slowly than rats fed the identical diet but allowed to drink 37 mM sodium chloride. On day 11, half of the salt-depleted animals received 37 mM sodium chloride in their drinking water. Sodium-deficient and supplemented rats were studied 1,2,5-6 and 11-12 days later. Urinary sodium rapidly rose from undetectable of 46 mEq/l urine within 1 day of supplementation and there was no further increase the next day, suggesting that extracellular fluid volumes were rapidly repleted. Food intake increased in the supplemented rats compared with the deficient animals but the difference in food intake equalled only 2.25 g/day for the first 2 days of supplementation. Over the last 12 days of the study, the slopes of both weight and length gains were equal in both the supplemented and the control group and significantly higher than those in the deficient rats. Over the course of the study, full catchup was not obtained in either length or weight. In addition to total weight and length gains, liver and kidney weights increased proportionately and by 5-6 days of supplementation were equivalent to the weights seen in the control group.(ABSTRACT TRUNCATED AT 250 WORDS)

Hyponatremia in the very young chronic peritoneal dialysis patient

Two anuric infants had recurrent hyponatremia during chronic peritoneal dialysis (PD). This occurred because at normal serum sodium concentrations ([Na]), Na losses from ultrafiltration (UF) were greater than the Na ingested from infant formula. Hyponatremia was corrected with increased oral Na intake or with increased dialysis solution [Na]. Anuric infants undergoing PD have hyponatremia because of their high UF requirements/body weight and the low Na content of proprietary infant formulas.

Growth rate in infants with impaired renal function

We report changes in renal function and growth rate in children with reduced renal function who were kept on a low normal phosphorus formula until 18 months of age. The relationship between serum creatinine values and derived creatinine clearance and residual renal function is reviewed regarding the risk of progressive loss of function. Expressing growth as growth velocity standard deviation scores over 6-month intervals gave a more accurate description of growth performance than did change in height standard deviation scores. A relationship between residual clearance and growth velocity was inferred. However, the growth of children with a less severe reduction in function was affected intermittently by intercurrent infections and inadequately treated acidosis and salt wasting. Children with a more severe reduction in function, despite maintenance on the low-phosphorus formula, had elevated serum parathormone levels. We conclude that following growth (as serial growth velocity standard deviation scores) in relation to other variables gives more insight into factors affecting growth in these children; the level of residual function affects growth potential but other complicating factors also have an effect.

Relative density of urine: methods and clinical significance

The physical properties and chemical composition of urine are highly variable and are determined in large measure by the quantity and the type of food consumed. The specific gravity is the ratio of the density to that of water, and it is dependent on the number and weight of solute particles and on the temperature of the sample. The weight of solute particles is constituted mainly of urea (73%), chloride (5.4%), sodium (5.1%), potassium (2.4%), phosphate (2.0%), uric acid (1.7%), and sulfate (1.3%). Nevertheless, urine osmolality depends only on the number of solute particles. The renal production of maximally concentrated urine and formation of dilute urine may be reduced to two basic elements: (1) generation and maintenance of a renal medullary solute concentration hypertonic to plasma and (2) a mechanism for osmotic equilibration between the inner medulla and the collecting duct fluid. The interaction of the renal medullary countercurrent system, circulating levels of antidiuretic hormone, and thirst regulates water metabolism. Renin, aldosterone, prostaglandins, and kinins also play a role. Clinical estimation of the concentrating and diluting capacity can be performed by relatively simple provocative tests. However, urinary specific gravity after taking no fluids for 12 h overnight should be 1.025 or more, so that the second urine in the morning is a useful sample for screening purposes. Many preservation procedures affect specific gravity measurements. The concentration of solids (or water) in urine can be measured by weighing, hydrometer, refractometry, surface tension, osmolality, a reagent strip, or oscillations of a capillary tube. These measurements are interrelated, not identical. Urinary density measurement is useful to assess the disorders of water balance and to discriminate between prerenal azotemia and acute tubular necrosis. The water balance regulates the serum sodium concentration, therefore disorders are revealed by hypo- and hypernatremia. The disturbances are due to renal and nonrenal diseases, mainly liver, cardiovascular, intestinal, endocrine, and iatrogenic. Fluid management is an important topic of intensive care medicine. Moreover, the usefulness of specific gravity measurement of urine lies in interpreting other findings of urinalysis, both chemical and microscopical.

Nutritional management of infants and toddlers with chronic renal failure

Normal renal function is an essential prerequisite for normal nutrition. Renal failure results in malnutrition and growth retardation, which are particularly marked when renal failure has its onset early in life. Conversely, the careful application of nutritional therapy can ameliorate the effects of renal failure and allow improved well being and growth and possibly retard the rate of progression of renal failure. Nutritional therapy includes the provision of an adequate energy intake, appropriate intakes of water, electrolytes, vitamins and minerals and regulation of protein and phosphorus intakes. In this paper the theoretical considerations underlying these objectives are reviewed and practical ways of achieving them with least disruption to the child and his family suggested.