Measurement of extracellular fluid volume in the neonate using multiple frequency bio-impedance analysis

Bioelectrical impedance analysis may be useful for cot-side monitoring of f luid balance in the neonatal intensive care unit (NICU). However the presen ce of cardio-respiratory monitoring equipment, non-ideal electrode placemen t and inability to obtain accurate crown-heel measurements may interfere wi th the ability to obtain reliable impedance data in this setting. This stud y aimed to investigate the effects of these factors on impedance analysis a nd to develop a prediction equation for extracellular fluid volume in the n eonate. The study found that cardiorespiratory monitoring had no significan t effect on multi-frequency impedance measurements. Placement of current de livering electrodes on the ventral rather than dorsal surfaces improved sep aration of current and voltage electrodes but did not alter impedance resul ts. Contralateral measurements were not significantly different to ipsilate ral measurements. In 24 infants, extracellular fluid volume was measured us ing corrected bromide space (CBS) and simultaneous impedance analysis was p erformed. There was good correlation between CBS and the impedance quotient F-2/R-0 where F is foot length and R-0 is resistance at zero frequency. Th e study concludes that despite many potential difficulties associated with impedance analysis in the NICU, reliable measurements of impedance can be o btained and further work to validate prediction equations for ECF is warran ted.