ASSESSMENT OF TOTAL-BODY WATER USING BIOELECTRICAL-IMPEDANCE ANALYSISIN NEONATES RECEIVING INTENSIVE-CARE

Aims - To determine the most suitable anthropometric and impedance mea sures and current frequency for the application of bioelectrical imped ance to neonates receiving intensive care; and to derive predictive mo dels for the estimation of total body water. Methods - Twenty eight ba bies (median gestational age 30.5 weeks, range 24-38; median birthweig ht 1.388 kg, range 0.690-3.510) were each studied once during the firs t week after birth. Total body water was first measured by the method of dilution of isotopic water ((H2O)-O-18). Bioelectrical measurements were made using the tetrapolar surface electrode method from four mai n distal limb positions (right hand-right foot; right hand-left foot; left hand-left foot; left hand-right foot), the left upper arm-left th igh position and the left scapula-right buttock position, and using si x frequencies ((500, 250, 100, 50, 10 and 5 kHz). Regression models, t o predict total body water, which were both independent and dependent of body weight on the day of study, were derived. Results - Resistance readings at 50 kHz obtained from the distal limb positions performed best. There was no difference between the distal limb positions. There was no difference in the goodness of fit of the models when using eac h of three indices of conductor length, foot, spine and sternum. The m odel total body water (litres) (TBW) = 0.016 + 0.674 bodyweight(kg)-0. 038 wt(2) + 3.84 foot length (cm)(2)/resistance (50 kHz in OHMS) perfo rmed best, accounting for 99.5% of the variation in TBW, with a 95% pr ediction interval of 165 ml. The model TBW = 0.144 + 15.518 foot lengt h (cm)(2)/resistance (50 kHz in ohms) accounted for 96.4% of the varia tion and had a 95% prediction interval of 420 ml. Conclusions - Bioele ctrical impedance analysis is a simple, non-invasive method of estimat ing total body water in neonates receiving intensive care. It can be a pplied to both the assessment of changes in body water and body compos ition.