Bioreactance: A new tool for cardiac output and thoracic fluid content monitoring during hemodialysis

Outpatient hemodialysis therapy (HD) can be associated with hemodynamic compromise. Bioreactance^® has recently been shown to provide accurate, noninvasive, continuous, measurements of cardiac output (CO) and thoracic impedance (Zo) from which thoracic fluid content (TFC) can be derived assuming TFC=1000/Zo. This study was designed to evaluate the changes in TFC in comparison with the traditional indices of fluid removal (FR) and to understand the trends in CO changes in HD patients. Minute-by-minute changes in TFC and CO were prospectively collected using the bioreactance system (NICOM^®) in HD patients of a single unit. Changes in body weight (ΔW), hematocrit (ΔHct), and amount of FR were also measured. Twenty-five patients (age 77 ± 11 years) were included. The TFC decreased in all patients by an average of 5.4 ± 7.9 kΩ⁻¹, weight decreased by 1.48 ± 0.98 kg, and FR averaged 2.07 ± 1.93 L over a 3- to 4-hour HD session. There were good correlations between ΔTFC and ΔW (R=0.80, P<0.0001) and FR (R=0.85, P<0.0001). ΔHct (4.13 ± 3.42%) was poorly correlated with ΔTFC (R=0.35, P=0.12) and FR (R=0.40, P=0.07). The regression line between FR and TFC yielded FR=1.0024−0.1985TFC; thus, a 1 kΩ⁻¹ change of Zo correlates with an ∼200 mL change in total body water. The change in CO (−0.52 ± 0.49 L/min m²) during HD did not correlate with FR (R=0.15, P=NS). Changes in TFC represented the monitored variable most closely related to FR. CO remained fairly constant in this stable patient cohort. Further studies in high-risk patients are warranted to understand whether TFC and CO monitoring can improve HD session management.