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Body water measurements in premature and older infants using H218O isotopic determinations
Insights
Accurate total body water measurements are achievable using small urine or plasma samples with H218O stable isotope dilution. This method provides reliable hydration status assessments in premature infants and recovering malnourished children.
Area of Science:
- Biomedical Science
- Pediatric Research
- Nutritional Science
Background:
- Accurate assessment of total body water (TBW) is crucial for clinical management, especially in vulnerable populations like premature infants and recovering malnourished children.
- Traditional methods for TBW measurement can be invasive or require larger sample volumes, posing challenges in pediatric studies.
Purpose of the Study:
- To evaluate the efficacy of H218O stable isotope dilution for measuring total body water in premature infants and recovering malnourished Peruvian children.
- To determine the optimal timing for sample collection (plasma and urine) to ensure accurate and reliable TBW estimates.
Main Methods:
- H218O stable isotope dilution was employed to measure total body water in two groups: premature infants and Peruvian children aged 6-36 months recovering from malnutrition.
- Gas-isotope-ratio mass spectrometry with an automated purification inlet system was used for analyzing small sample volumes (50 microliters) of urine and plasma.
Main Results:
- Reliable total body water estimates were obtained using minimal sample volumes.
- Isotope equilibration in plasma was substantially complete by 2-4 hours post-dose, with estimates closely matching 6-hour values.
- Urine samples collected 5-7 hours post-dose showed high correlation (r=0.96-0.99) with plasma-based TBW values, indicating accurate hydration status assessment.
Conclusions:
- H218O stable isotope dilution is a reliable and sensitive method for determining total body water in infants and young children.
- Minimal plasma or urine sample volumes are sufficient for accurate TBW assessment, facilitating clinical application.
- Optimized urine collection times (5-7 hours post-dose) provide highly correlated results with plasma-based measurements.
Abstract:
Total body water was measured by H218O stable isotope dilution in two groups: in premature infants without complications, who were studied from 8 d of age until discharge; and in Peruvian subjects aged 6-36 mo, who were in the long-term convalescent stage of recovery from malnutrition. Results indicated that reliable total body water estimates can be obtained from sample volumes as small as 50 microliters of urine or plasma using a gas-isotope-ratio mass spectrometer equipped with an automated purification inlet system. Results from 21 studies in 10 Peruvian infants indicated substantially completed isotope equilibration in plasma by 2 h after the dose; total body water estimates from the 2-h samples averaged 98.7% (+/- 4.1) of 6-h values. Samples obtained at 4-h postdose gave total body water estimates that averaged 99.0% (+/- 2.9) of the 6-h value, showing essentially complete equilibration and reduced variability. Total body water estimates from urine samples collected 3-5 h postdose were closely correlated with 6-h, plasma-based total body water values in both premature and older infants; however, some reduction in variability was observed when urine collection was extended to 5-7 h, at which time urine-based estimates averaged 98.8% (+/- 2.0) and 100.7% (+/- 3.1) of plasma-based values for prematures and older Peruvian infants, respectively. The correlation between 5-7 h urine-based estimates of total body water with plasma-based values was r = 0.96 for 30 studies in prematures and r = 0.99 for 57 studies in older Peruvian infants.(ABSTRACT TRUNCATED AT 250 WORDS)