Intravenous Fluid Challenge Decreases Intracellular Volume: A Bioimpedance Spectroscopy-Based Crossover Study in Healthy Volunteers

Abstract

The effects of intravenous fluid therapy on fluid compartments and hemodynamics of the human body remain enigmatic. We therefore tested the efficacy of bioimpedance spectroscopy in a crossover study, where 15 males received 0.5 ml/kg/min ELO-MEL-isoton (osmolarity = 302 mosmol/l) during 60 minutes, or nothing at all. In group "Fluid", fluid load increased from -0.2 ± 1.0 l extracellular volume at baseline to its maximum of 1.0 ± 0.9 l in minute 70, and remained continuously elevated throughout minute 300. In group "Zero", fluid load decreased from 0.5 ± 1.1 l at baseline to its minimum of -1.1 ± 1.1 l in minute 300. In group "Fluid", intracellular volume decreased from 26.8 ± 3.9 l at baseline to its minimum of 26.0 ± 3.9 l in minute 70, and remained continuously decreased throughout minute 300. In group "Zero", intracellular volume increased from 26.5 ± 3.8 l at baseline to its maximum of 27.1 ± 3.9 l in minute 120, and decreased thereafter. In group "Fluid" compared to "Zero", systolic blood pressure was significantly higher, from minute 50-90. In conclusion, intravenous fluid therapy caused a clinically meaningful, sustained increase in fluid load, and a decrease in intracellular volume. These data raise interest in studying fluid administration by the gastrointestinal route, perhaps even when managing critical illness.

Figure 1

Study flow chart. ^#Values are reported as median (1^st quartile; 3^rd quartile). N = number of participants.

Figure 2

Volume status, hemodynamics, urine output and body weight during the fluid intervention (“Fluid”) and thirsting (“Zero”). Time course of fluid load (a), intracellular volume (b), extracellular volume (c), total body volume (d), relative fluid load (e), hemodynamics (f), urinary excretion (g) and body weight (h). Values are depicted as means ± standard errors of the means. Significant differences were determined by Student’s t-test and are marked (black stars) at the 0.05 probability level. U marks time point of urinating in an upright position.