161 ASSESSMENT OF TOTAL BODY WATER AND WEIGHT IN NEONATES USING BIOELECTRICAL IMPEDANCE ANALYSIS

Abstract

Top of pageAbstract Bioelectrical impedance analysis (BIA) is a non-invasive technique that has been used to measure total body water (TBW). In view of the close relationship between TBW and weight in newborn babies, we hypothesised that it might also be possible to derive an estimate of weight from BIA. Twenty eight babies (median gestational age 30.5 weeks (range 24 - 38); median birth weight 1.388 kg (range 0.690 - 3.510)) were studied once during the first week after birth. TBW was assessed by dilution of isotopic water (H218O). Bioelectrical measurements were made using the tetrapolar surface electrode method. The model, TBW = 0.135 + 0.516 wt + 4.074 L2/R accounted for 99.4% of the variation in TBW and log TBW = −0.188 + 0.895 log wt, 98.8% of this variance. The former model improved prediction of TBW in larger babies but there was no difference in prediction between the two models in smaller babies. The model, body weight = 0.018 + 0.809 birthweight + 3.49 L2/R accounted for 99.6% of the variation in body weight (TBW, litres; wt, body weight on study day in kg; L, foot length in cm; R, resistance at 50 kHz in ohms.) In the most immature babies, the prediction of TBW from BIA, offers no improvement over prediction from body weight alone. It does improve prediction in larger babies. BIA may have a clinical role in the longitudinal assessment of body weight if, as is often the case, a baby is loo unwell to be weighed formally.