Bioelectrical impedance vector values in a Spanish healthy newborn population for nutritional assessment.

INTRODUCTION: Vector bioimpedance analysis (BIVA) can be very useful for the evaluation of body composition, hydration, and nutritional status in infants and newborns. The objective of this study was to determine the impedance vector distribution for a group of healthy newborn Spanish children.

METHODS: This was a cross-sectional, descriptive study conducted with 154 healthy, Spanish newborns (gestational age: 37-41 weeks) aged 24 to 72 hours (79 males, 75 females). Weight, height, and cephalic-circumference were determined. Resistance and reactance were measured with a single-frequency impedance analyzer at 50 kHz (tetrapolar analysis). The newborns' specific 95% confidence intervals of the mean vectors and the 95%, 75%, and 50% tolerance intervals for the individual vector measurements were plotted using R and Xc components standardized by the subjects' lengths. The mean impedance vectors were compared with Hotelling's-T2 test for vector analysis (significance level: P < .05).

RESULTS: The newborns exhibited gender-related differences in the mean impedance vector (mean [SD] R/H: 833.6 [97.5] Ohm/m in males vs 918.2 [107.7] Ohm/m in females; mean [SD] Xc/H: 91.3 [34.7] Ohm/m in males vs 95.6 [23.2] Ohm/m in females). No statistically significant differences in the mean impedance vectors were observed according to days of life. Lower values of resistance and slightly higher reactance values were observed in the healthy Spanish newborns compared to Italian newborns.

CONCLUSIONS: New tolerance ellipses were constructed for healthy Spanish newborns. These data allow detecting alterations in the hydration status and cell mass in term newborns in the first 3 days of life.