Carotid Doppler Ultrasound for the Measurement of Intravascular Volume Status
Condition: Hypotension; Sepsis
MeSH terms: Hypotension
Study type: Interventional

Summary: 
      Ultrasound represents an attractive non-invasive method to assess hemodynamic status.
      Understanding dynamic changes in hemodynamics in situations such as hypovolemia, sepsis, and
      cardiogenic shock can potentially help improve patient care. However, the inter-rater
      reliability and accuracy of how various ultrasound measurements reflect dynamic changes in
      physiology remains incompletely understood. Overall our aims are to investigate the use of
      ultrasound in a controlled setting, specifically using lower body negative pressure (LBNP),
      which can simulate hypovolemia at varied levels in human volunteers.

      Aim 1: To determine the change in carotid blood flow (measured by velocity time integral,
      VTI) in subjects undergoing simulated hypovolemia at LBNP levels that precede vital sign
      changes.

      Hypothesis: Carotid VTI will demonstrate significant changes that precede vital sign changes
      in simulated hypovolemia.

      Aim 2: To compare transcranial color Doppler indices of cerebral blood flow with carotid
      blood flow, as assessed by VTI of the common carotid artery.

      Hypothesis: Changes in transcranial color Doppler indices of cerebral blood flow will be
      mirrored by changes in carotid blood flow, indicating carotid VTI is an adequate surrogate
      for measuring cerebral blood flow in variable states of central hypovolemia. However, if
      cerebral blood flow remains more constant than carotid blood flow throughout varying levels
      of hypovolemia, our assumption is that cerebral autoregulation alters the relationship
      between carotid and cerebral blood flow. The more complex procedure of Transcranial Doppler
      ultrasound (TCD) must be performed to obtain valid assessments of cerebral blood flow.
    

Detailed description: 
      Study Design: This is a prospective laboratory study using human volunteers.

      Study Setting and Subjects: The study will take place in The John B. Pierce Laboratory where
      volunteers will be subjected to lower body negative pressure using the on-site LBNP chamber.

      Protocol: Study subjects will be instructed to refrain from caffeine, alcohol, or cigarettes
      within 12 hours of the protocol, but will otherwise be allowed their routine oral intake
      prior to enrollment. The chamber is constructed of a sealed wood and acrylic box that is
      connected to a vacuum. Subjects will be placed into the chamber, which is sealed to the level
      of their pelvis by a neoprene skirt. Chamber pressure is transduced to an electronic digital
      manometer. The pressure in the chamber will reduced rapidly and held for 15-minute intervals
      at -5, -10, -15, and -20 mm Hg. If the subject becomes lightheaded, nauseated, or does not
      tolerate the test run in any way; negative pressure will be stopped.

      Subjects will be monitored with continuous electrocardiogram monitoring, a standard automated
      blood pressure cuff, and a noninvasive beat-to-beat hemodynamic monitor (Finometer, Finapres
      Medical Systems, Amsterdam, The Netherlands). All carotid ultrasound measurements will be
      performed by specifically trained emergency physicians, using a Philips ultrasound machine
      (Philips Medical Systems, Andover, MA) equipped with phased and linear array probes
      programmed with Doppler capability. For transcranial Doppler imaging, we will use a 5- to
      1-MHz sector array transducer and an Iu-22 ultrasound system (Philips Healthcare, Best, the
      Netherlands). Duplex sonography will be performed at the lower end of the frequency range
      (1-2 MHz) for better sound wave penetration of selected bone windows. For both the common
      carotid artery and transcranial portion of this study, we will obtain spectral Doppler
      waveform tracings and record measurements of corresponding vessel diameters. We will use data
      generated from software analysis of these spectral tracings to calculate hemodynamic
      parameters of interest to our study. Calculations are based on Bernoulli's principles of
      fluid dynamics.
    

Intervention name(s): Point of Care Ultrasound
Intervention type(s): Other
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Diagnostic
Keywords: hemodynamics; ultrasonography