Dynamic Skinfold Thickness Measurements: a Noninvasive Estimate of Neonatal Extracellular Water Content

摘要

Summary: Application of a Harpenden caliper to a neonate's skinfold results in an exponential decline of the skinfold thickness, stabilizing within 50–60 sec. In order to elucidate the meaning of this decline, simultaneous measurements of skinfold thickness (SFT, by Harpenden caliper connected to a chart recorder), corrected bromide space (CBS, in ml/kg), plasma volume (ml/kg, by T-1824 dilution) and interstitial water (IW, ml/kg = CBS-plasma volume) were obtained in 18 term and 18 preterm neonates. Skinfold thickness was measured at the midtricipital (MT) and subscapular (SS) sites. The magnitude of SFT decline was estimated as the difference between 0–60 sec readings expressed in % of 0 second reading (%ΔSFT). The rate of SFT decline was estimated as the slope of the semilogarithmic plot from 4–20 sec after caliper application (SΔSFT).The 36 neonates whose birthweights ranged from 620–3700 g and whose gestational ages ranged from 27–41 wk were studied within 12 h of birth. Mean CBS, IW, %ΔMT, %ΔSS, SΔMT and SΔSS were higher in preterm than in term neonates (P P = 0.009), but the difference disappeared after exclusion of six polycythemic term neonates from the calculations. The magnitude of SFT decline correlated well with both CBS (%ΔMT versus CBS: r = 0.71 and %ΔSS versus CBS: r = 0.71) and IW (%ΔMT versus IW: r = 0.71 and %ΔSS versus IW: r = 0.70). The rate of decline correlated moderately but highly significantly with both CBS (SΔMT versus CBS: r = 0.50 and SΔSS versus CBS: r = 0.42) and IW (SΔMT versus IW: r = 0.51 and SΔSS versus IW: r = 0.43). Exculsion of five neonates less than 30 wk in gestation improved the correlations with both %ΔSFT and SΔSFT.These data suggest that the decline in SFT measurements after caliper application results from the expression of subcutaneous IW from the skinfold and that both the amount of water expressed and the rate of its expression increase linearly with the amount of extracellular and IW in the body.Speculation: Both the magnitude and the rate of skinfold thickness compressibility or expressibility appear to be intimately related to extracellular and interstitial water contents of the neonatal body. Dynamic skinfold thickness measurements may therefore be noninvasive estimates that are representative of body hydration and that may be used in research on neonatal body composition as well as clinically to evaluate hydration status of sick neonates.