title: Dynamic Limb Bioimpedance and Inferior Vena Cava Ultrasound in Patients Undergoing Hemodialysis.
abstract: Assessment of volume status in critically ill patients poses a challenge to clinicians. Measuring changes in the inferior vena cava (IVC) diameter using ultrasound is becoming a standard tool to assess volume status. Ultrasound requires physicians with significant training and specialized expensive equipment. It would be of significant value to be able to obtain this measurement continuously without physician presence. We hypothesize that dynamic changes in limb's bioimpedance in response to respiration could be used to predict changes in IVC. Forty-six subjects were tested a hemodialysis session. Impedance was measured via electrodes placed on the arm. Simultaneously, the IVC diameter was assessed by ultrasound. Subjects were asked to breathe spontaneously and perform respiratory maneuvers using a respiratory training device. Impedance (dz) was determined and compared with change in IVC diameter (dIVC; r = 0.76, p < 0.0001). There was significant relationship between dz and dIVC (p< 0.0001). Receiver-operator curves for dz at thresholds of dIVC (20% to70%) demonstrated high predictive power with areas under the curves (0.87-0.99, p < 0.0001). This evaluation suggests that real-time dynamic changes in limb impedance are capable of tracking a wide range of dynamic dIVC. This technique might be a suitable surrogate for monitoring real-time changes in dIVC to assess intravascular volume status.
authors.affiliation: From the *Department of Emergency Medicine, †Department of Biomedical Engineering, ‡Division of Nephrology, Department of Internal Medicine, §Department of Mechanical Engineering, and ¶Michigan Center for Integrative Research in Critical Care (MCIRCC), University of Michigan, Ann Arbor, Michigan.
authors.forename: Mohamad H
authors.initials: MH
authors.lastname: Tiba
authors.forename: Barry
authors.initials: B
authors.lastname: Belmont
authors.forename: Michael
authors.initials: M
authors.lastname: Heung
authors.forename: Nik
authors.initials: N
authors.lastname: Theyyunni
authors.forename: Robert D
authors.initials: RD
authors.lastname: Huang
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Fung
authors.forename: Amanda J
authors.initials: AJ
authors.lastname: Pennington
authors.forename: Brandon C
authors.initials: BC
authors.lastname: Cummings
authors.forename: Gerard T
authors.initials: GT
authors.lastname: Draucker
authors.forename: Albert J
authors.initials: AJ
authors.lastname: Shih
authors.forename: Kevin R
authors.initials: KR
authors.lastname: Ward
mesh_terms: D000328:Adult; D000368:Aged; D001132:Arm / Q000503:physiopathology; D017097:Electric Impedance; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010865:Pilot Projects; D006435:Renal Dialysis; D014463:Ultrasonography; D014682:Vena Cava, Inferior / Q000000981:diagnostic imaging*