Monitoring intracellular, interstitial, and intravascular volume changes during fluid management procedures

Abstract

The bioimpedance spectroscopic (BIS) analytical algorithm described in this report allows for the non-invasive measurement of intravascular, interstitial, and intracellular volume changes during various fluid management procedures. The purpose of this study was to test clinical use feasibility and to demonstrate the validity of the BIS algorithm in computing compartmental volume shifts in human subjects undergoing fluid management treatment. Validation was performed using volume changes recorded from 20 end stage renal disease (ESRD) patients. The validation procedure involved mathematically deriving post hoc hematocrit profiles from the BIS data-generated fluid redistribution time profiles. These derived hematocrit profiles were then compared to serial hematocrit values measured simultaneously by a CritLine® monitor during 60 routine hemodialysis (HD) sessions. Regression and Bland Altman analyses confirm that the BIS algorithm can be used to reliably derive the continuous and real time rates of change of the compartmental fluid volumes. Regression results yielded a R2 > 0.99 between the two measures of hematocrit at different times during dialysis. The slopes of the regression equations at the different times were nearly identical, demonstrating an almost one to one correspondence between the BIS and CritLine® hematocrits. Bland Altman analyses show that the BIS algorithm can be used interchangeably with the CritLine® monitor for the measurement of hematocrit. The present study demonstrates for the first time that BIS can provide real-time continuous measurements of compartmental intravascular, interstitial and intracellular fluid volume changes during fluid management procedures when used in conjunction with this new algorithm.

The source of net ultrafiltration during hemodialysis is mostly the extracellular space regardless of hydration status

“…Recently, Montgomery et al. demonstrated that a new bioimpedance spectroscopic (BIS) algorithm can be used to provide real‐time continuous measurements of IC, interstitial, and intravascular fluid volume changes during fluid management procedures . In addition, Van der Sande et al.…”

A system to monitor segmental intracellular, interstitial, and intravascular volume and circulatory changes during acute hemodialysis

“…Regression and Bland Altman analyses were used to compare the BIS data and CritLine ® hematocrits at sequential times during the 60 chronic HD sessions with the patients in a horizontal position. The statistical and graphical evidence obtained [31] confirmed that the BIS system reliably monitors the continuous and real time rates of change of the fluid volumes of the three compartments in the chronic treatment setting.…”

“…Details of the analytical algorithm used to derive individual fluid compartment volumes from the impedance spectroscopic recordings are given in previous articles [30][31][32]. We hypothesize that this new instrument will be able to quantify changes in the three fluid compartments as fluid volume is removed during hemodialysis.…”

Changes in serum osmotic pressure following haemodialysis treatments lead to changes in bioimpedance spectroscopy estimates of lean and adipose tissue

“…Conversely when sOP decreased post dialysis, then LTM and BCM increased, and ATM fell. Previous bioimpedance studies have variously reported a fall in fat free mass and increase in fat mass, or an increase in ICW and BCM [8]. Over estimation of fat free mass has been ascribed to increased ECW pre-dialysis, as muscle contains more water than fat.…”

“…However, the model is based on the concept of normally hydrated tissue, and tissue hydration will vary between haemodialysis patients due to hydration status, but also electrolyte balance and retention of uraemic solutes. During dialysis not only are there changes in hydration status but also electrolyte fluxes and removal of uraemic solutes, leading to differences in estimation of ECW and ICW during dialysis [8,9]. As such this will lead to changes in intra-cellular osmolality and cell hydration, which will vary between patients, leading to differences in tissue hydration status compared to the bioimpedance estimated normo-hydrated state [10].…”