Bioimpedance Spectroscopy in Humans During Acute Fluid Volume Expansion With Different Crystalloid Solutions

The resistance of the human body to the flow of alternating current is thought to be related to the volume of fluid within the body. The acute change in fluid status of the human body alters the body resistance. This change can be measured accurately with bioelectrical impedance and previous experiments confirmed this observation. However, previous experiments using a piglet model and subsequently humans, suggested that the changes observed is a result of changes in salt instead of body water.

An experiment has shown that bioimpedance analysis (BIA) was able to detect changes in total body resistance when different electrolyte solutions were infused. The changes in resistance were related to changes in osmolarity and electro-ionic state, not to volume of water infused. Therefore, BIA measures principally the electro-ionic state. Thus a measurement of fluid volume can be indirectly obtained from BIA. However, in the non-steady state such as acute fluid volume expansion, the measurement of water volume cannot be performed accurately.

In this study, we will be administering sodium bromide in oder to measure extracellular water via the bromide solution technique. Despite the interesting observations, the human study described above was underpowered. Therefore, we aim to validate the observations that have been previously made through carrying out an appropriately powered study with an adequate sample size to validate the observations noted.