Urine Sodium Concentration as a Marker of Poor Growth in Children with Intestinal Failure

BACKGROUND: Children who have had a significant small bowel resection often have difficulty growing adequately due to fluid and electrolyte losses in their stool. Specifically, growth is impaired when total body sodium depletion occurs. Urinary sodium concentration (UNa) is a more sensitive marker than serum sodium (less than or equal to 30 mmol/L considered low), and is used to monitor total body sodium status. The objective of this study was to determine the frequency of low UNa in children after significant bowel resection, and determine if it is associated with poor growth. METHODS: After IRB approval (Protocol #032016-015), a retrospective chart review of children (<19 years) who underwent small bowel resection (requiring parenteral nutrition for > 6 weeks post-operatively) cared for at Children's Health from 2010 to 2016 was performed. Patient characteristics, reason for small bowel resection, intestinal anatomy, nutritional intake, anthropometric measurements, and urine and serum electrolytes were collected. Z-scores were calculated from WHO and CDC standard growth charts. Anthropometric values were compared between children with a UNa less than or equal to 30 mmol/L and > 30 mmol/L. Statistical analysis was completed using Mann-Whitney and Pearson's correlation coefficient, providing both 95% confidence intervals and p-values. Analysis was performed with SAS 9.4 (Cary, NC). RESULTS: Thirty-eight children with significant bowel resection were included in the study. Patients had a median small bowel length of 50 cm (5-315 cm) and median % expected small bowel remaining of 27% (2-91%). The median UNa was 44 mmol/L, and 10 patients (26%) had a UNa less than or equal to, to 30 mmol/L. Only 1 patient demonstrated hyponatremia (serum Na = 130 meq/L). There was a positive correlation between UNa and both sodium intake (0.32, 95% CI [0.01, 0.57], p=.04), and body mass index (0.35, 95% CI [0.05, 0.60], p=.03), but no significant correlation with small bowel length. Children with UNa less than or equal to 30mmol/L had significantly lower Z-scores for weight (median -2.5 vs. -0.44, p=.0252) compared to those with UNa > 30mmol/L. CONCLUSION: Children with malabsorption after significant small bowel resection are at increased risk for sodium depletion and impaired growth. Patients with UNa less than or equal to 30 mmol/L should receive additional sodium supplementation to maximize growth.