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Urinary urea nitrogen (UUN) excretion in critically ill children correlates linearly with body surface area (BSA). This finding allows for accurate comparisons across diverse patient groups, aiding in nutritional assessment and protein catabolism monitoring.
Area of Science:
- Pediatric critical care medicine
- Clinical biochemistry
- Nutritional science
Background:
- Urinary urea nitrogen (UUN) excretion is a key indicator of protein metabolism and nitrogen balance.
- Accurate assessment of UUN is crucial for nutritional management in critically ill children.
- Variability in age and clinical status in pediatric intensive care units (PICUs) can complicate UUN interpretation.
Purpose of the Study:
- To evaluate urinary urea nitrogen (UUN) excretion as a marker of protein catabolism in critically ill children.
- To establish a reliable method for comparing UUN excretion across a wide range of pediatric patients.
- To investigate the relationship between UUN excretion and body surface area (BSA) in this population.
Main Methods:
- Assayed daily UUN excretion in 32 children (2 months to 15 years) over 1-10 days in an intensive care unit.
- Utilized linear regression analysis to correlate UUN excretion (mg/kg/day) with body surface area (BSA).
- Compared UUN excretion data between mechanically ventilated and spontaneously breathing children, and across diagnostic subgroups.
Main Results:
- Daily UUN excretion averaged 4.38 ± 2.22 gm/sq m (171 ± 89 mg/kg) across 121 patient days.
- A strong linear relationship was found between average daily UUN excretion and BSA (mg UUN = 4,421.5 x BSA; r² = .903).
- UUN excretion was evenly distributed around the BSA regression line, irrespective of mechanical ventilation status or diagnostic subgroup, indicating individual variability.
Conclusions:
- Urinary urea nitrogen (UUN) excretion is reliably predicted by body surface area (BSA) in critically ill children.
- The established linear relationship facilitates valid comparisons of UUN excretion among pediatric patients of varying ages and diagnoses.
- Individual variability in UUN excretion is significant and independent of diagnostic or therapeutic subgroups, highlighting the need for personalized assessment.
Abstract:
Urinary urea nitrogen (UUN) excretion as an index of both total nitrogen excretion and protein catabolism was assayed in 32 children (aged 2 months to 15 years, median 6 years) (50% mechanically ventilated) during an intensive care unit course of one to ten days (median three days). The daily UUN excretion was 4.38 +/- 2.22 gm/sq m (171 +/- 89 mg/kg) (N = 121 patient days). The average daily UUN excretion (N = 32 children) was well described by a linear regression equation for square meters of body surface area (BSA) (milligrams of UUN = 4,421.5 x BSA; r2 = .903). This linear relationship permitted the valid comparison of both individuals and subgroups despite wide age differences. Excretion data in the mechanically ventilated vs the spontaneously breathing children, and in four diagnostic subgroups (Reye syndrome, seven; sepsis, six; elective surgery, seven; and miscellaneous, 12) were evenly distributed about the regression line for body surface area. Variability in average daily UUN excretion was on individual basis, and was independent of diagnostic or therapeutic subgroup.