Wearable and noninvasive monitoring of fluid shifts: A pilot study assessing a novel bioimpedance sensor during lower body negative pressure

Fluid extravasation is a prominent feature of several disease processes in acute and critical illness. Bioimpedance at frequencies representing extracellular and total resistance offers an opportunity to monitor fluid shifts. The aim of the present study was to explore if a novel wearable bioimpedance device could monitor fluid shifts during lower body negative pressure (LBNP). Eleven subjects underwent 40 min of LBNP at 30 mmHg. Bioimpedance was measured on the leg, upper back, and thoracic midaxillary line. Changes in resistance were compared using mixed linear regression. Further, hemoglobin and albumin concentrations were measured. Ten subjects completed the protocol. Compared to baseline, both extracellular and total resistance changed to the end of the LBNP exposure at all measurement sites. The mean extracellular resistance changed as follows: leg -6.6% (SD 3.1; p < 0.001), upper back 4.1% (SD 3.5; p < 0.001), and midaxillary line 6.3% (SD 2.8; p < 0.001). The wearable bioimpedance sensor detected the expected extracellular fluid shifts occurring with LBNP. Further clinical studies to explore if fluid extravasation in common pathologic conditions can be measured are warranted.