Perioperative monitoring of total body water by bio-electrical impedance in children undergoing open heart surgery

Abstract

Knowledge of the changes in total body water (TBW) following cardiacsurgery (OHS) in children would be of value in fluid therapy and inresearching the causes and management of capillary leak. We have validateda bioelectrical impedance technique (BEI) for non-invasive estimation ofTBW in children after OHS. We report the use of this method in alongitudinal study. Twenty patients (mean age 4.7 years +/- 3.5 (SD), meanweight (WT) 16.2 kg +/- 1 kg) undergoing a variety of complex OHSprocedures were studied from 1 day preoperatively to 4 dayspostoperatively. Anaesthetic and basic bypass (CPB) techniques wereuniform. Six patients underwent CPB at less than 20 degrees C, 10 at 20degrees - 25 degrees C and 4 at 26 degrees - 33 degrees C. TBW (BEI), core(ctemp) and peripheral (ptemp) temperatures and fluid balance (TFB) wererecorded at frequent intervals. TBW (by BEI) rose (P less than 0.001)following CPB in all patients from 62% +/- 9% (SD) body weightpreoperatively to 73% +/- 13% in the ICU (an increase of 11% +/- 5%). TBWremained significantly elevated until the 3rd postoperative day.Multivariate analysis (MVA) confirmed that TBW was significantly related toTFB, but not to ctemp or ptemp. MVA also revealed smaller patient size(height and weight), younger age and longer CPB time as incremental riskfactors for the rise in TBW. Conclusions: (1) BEI permits the non-invasivestudy of TBW in children after OHS, when TBW variation may be considerable.(2) The smaller the child and the longer the CPB, the greater the rise inTBW. (3) The technique should be a valuable tool in researching the majorwater fluxes associated with CPB in children.