Estimation of total body water in very-low-birth-weight infants by using anthropometry with and without bioelectrical impedance and H2[(18)O].

The usefulness of bioelectrical impedance (BI) with anthropometry to measure total body water (TBW) was evaluated in very-low-birth-weight (VLBW) infants. A specific regression equation to measure TBW in a VLBW population was developed by simultaneously using the H2[(18)O] dilution method and BI in 12 infants with a gestational age of 24-30 wk and weighing <1200 g at birth. After an oral dose of H2[(18)O], the tracer dilution was measured in expired carbon dioxide. BI measurements were made with a model BIA-101 apparatus (RJL Systems, Detroit). Electrodes were placed in the standard position as well as proximally on the leg and the forearm. The best correlation was observed between body weight and TBW (r = 0.989). For BI, the best correlation was obtained when gestational age was used as a covariable along with body weight and crown-heel length (r = 0.985). The correlation was comparable with proximal electrode placement (r = 0.985). The new correlation was evaluated in 6 infants weighing < 1008 g. A significant correlation between BI and H2[(18)O]-measured TBW was observed (r = 0.988). Published regression equations for infants consistently gave higher estimates of TBW in another group of 14 infants weighing <1200 g than did the new correlations. TBW represented 84-95% of body weight in these VLBW infants. TBW could be computed simply from body weight alone. Use of BI and length as covariables did not add significantly to the estimate of TBW in VLBW infants.