Clinical Trial Details
— Status: Completed
Administrative data
| NCT number |
NCT02366507 |
| Other study ID # |
BPD-02 |
| Secondary ID |
|
| Status |
Completed |
| Phase |
|
| First received |
|
| Last updated |
|
| Start date |
July 2014 |
Study information
| Verified date |
February 2016 |
| Source |
Wake Forest University Health Sciences |
| Contact |
n/a |
| Is FDA regulated |
No |
| Health authority |
|
| Study type |
Observational
|
Clinical Trial Summary
Traditional devices to measure blood pressure include automatic sphygmomanometer (pressure)
cuff systems or manual blood pressures obtained by auscultation (listening with a
stethoscope). Both these techniques fail to provide accurate and consistent blood pressure in
the hypotensive (low blood pressure) state, which is often encountered in emergency
departments and intensive care units. Alternately, invasive arterial pressure measurement is
time-intensive, painful, expensive, and risks include bleeding, infection, and neurovascular
injury.
In clinical practice, the Doppler velocimetry system is occasionally used in hypotensive,
critically-ill patients when an immediate systolic blood pressure measurement is vital for
clinical and therapeutic management. With a technique similar to that used to obtain a manual
blood pressure, the Doppler velocimetry system can be used in place of the auscultation of
the brachial pulse to accurately determine the systolic blood pressure. It is currently
unknown whether additional information can be obtained by evaluation of the Doppler waveform
in healthy vs. critically-ill patients. The goal is this project is to digitally record
Doppler waveforms of critically-ill patients in the Emergency Department (ED) via a standard
8MHz (fetal) Doppler probe, correlate the Doppler readings with current blood pressure and
heart rate, and determine if waveform shapes and parameters are predictive of hemodynamic
compromise.
Description:
Background/Significance:
Hypotension is common and predicts worse outcomes. Arterial hypotension, defined as an
arterial systolic blood pressure (BP) less than 90 mmHg in adults, represents the hallmark of
critical illness. Accurate arterial BP measurement is essential to deliver effective
treatment, to guide resuscitation, and to assess interventions. Non-traumatic hypotension has
been documented in as many as 19% of Emergency Department (ED) patients and those patients
with hypotension have a 10-fold increased risk of sudden, unexpected in-hospital death.(1)
Early hypotension is associated with increased mortality in survivors of cardiac arrest,
stroke, and STEMI,(2-4) stressing the need for a tool to rapidly and accurately identify BP
trends in order to effectively direct resuscitative measures. Additionally, Doppler waveforms
may provide additional clues of impending hemodynamic deterioration before overt hypotension
or shock ensues.
Disadvantages of the current system - The current initial standard for BP measurements in
most hospitals is via an automated non-invasive BP device that uses oscillometric technology.
This method has numerous limitations including non-continuous monitoring, missing or delays
in identifying hypotensive episodes, inaccuracy or inability to measure BP due to various
reasons including inaccurate cuff size or severity of hypotension. In one study, 34% of
patients had a BP discrepancy of ≥ 20 mmHg with the oscillometric device compared to
intra-arterial BP monitoring due to incorrect cuff size.(5) Oscillometric devices are
sufficient for use in many clinical situations; however, notable exceptions include patients
that are severely hypertensive, hypotensive, with arrhythmias, after trauma, and other
critical clinical scenarios, whereby manual auscultatory BP measurement is preferred.(6) Even
in non-critically ill patients, validation data of oscillometric measurements has been called
into question.(7) The alternative to oscillometric devices is an intra-arterial catheter.
Although accurate, intra-arterial catheters are invasive, technically difficult to insert,
expensive, time-intensive, painful, and with risks including bleeding, infection, and
neurovascular injury. Current guidelines for management of critically ill patients suggest
intra-arterial BP measurement is preferred over automatic oscillometric non-invasive BP
measurement. Despite this, in a recent survey of intensivists, 73% used non-invasive BP
measuring devices in hypotensive patients.(8) For the above reasons, researchers have been
investigating newer technology to replace the oscillometric technology; examples include
Doppler and photoplethysmographic devices.(9;10) Newer technology- The research and
application of Doppler technology for measuring BP is in its infancy and has yet to be fully
realized. The benefits of such a device would include an accurate, non-invasive means to
measure BP in critically-ill patients. Due the high-risk of missing hypotension, the
possibility exists to commercialize the prototype for broader clinical use in non-critically
ill patients as well. The accuracy of Doppler velocimetry is one important advantage. In an
animal study comparing three indirect BP measuring instruments- a Doppler ultrasonic
flowmeter, an oscillometric device, and a photoplethysmograph- to direct arterial pressure in
cats, the Doppler and photoplethysmographic devices had the highest overall accuracy. (10) In
clinical practice, when the initial automatic oscillometric BP device is unable to obtain a
measurement due to hypotension, the manual Doppler technique is a common practice due to its
reliability and referenced in one study as the "gold standard".(11) However, accurate
systolic BP measurement is only one parameter of the device. The Doppler signal received from
the arterial flow through the vessel has incredible potential to identify strength of pulse
and other auditory queues. This has been well established in peripheral arterial disease,
with descriptive terms used such as monophasic, biphasic, or triphasic pulses identified by
Doppler. The novel device has the potential to identify a "sick" pulse as determined by
changes in the Doppler waveform prior to hypotension ensues, as often, hypotension is very
late in the course of the disease process. To date, there is no automatic
sphygmomanometer/Doppler apparatus available.
This project will provide data to further the development of a novel blood pressure
monitoring device that will enable non-invasive and near-continuous blood pressure monitoring
and other hemodynamic information on critically-ill patients. Data from healthy volunteers
using a standard 8MHz (fetal) Doppler probe have already been collected in a companion
protocol in place at the University of North Carolina at Charlotte (UNCC).
Research Strategy:
1. Significance Identification of shock states before overt clinical evidence of shock
(i.e., hypotension) is challenging. Determining whether Doppler-measured arterial
waveforms can serve as a useful marker to identify hemodynamic compromise before shock
ensues is unknown.
2. Approach Hypothesis: Doppler waveform patterns in critically-ill hypotensive patients
have a unique and identifiable pattern.
Objectives:
1. Doppler waveforms will be collected from the brachial arteries of critically-ill
patients that present to the ED with overt evidence of shock.
This pilot study will allow us to obtain Doppler measurements in critically-ill patients
for comparison to non-critically-ill patients collected previously in an IRB-approved
study conducted at UNCC by the Co-PI.
Doppler signal measurements will be obtained from 20 critically-ill patients with
evidence of shock (i.e., hypotension with SBP < 90) in Emergency Department at Carolinas
Medical Center. Eligible patients will be identified from the Code Sepsis clinical
protocol alert by PCL currently utilized for other departmental studies or by direct
report from the PI while working in the ED. Patients or a legally authorized
representative will be approached for informed consent. The 8MHz Doppler probe, (fetal
ultrasound probe), will be applied to the brachial artery, and the position adjusted
until an adequate signal has been obtained. Doppler wave form data will be collected
over the course of a few minutes. It is anticipated that the patients will experience
minimal to no discomfort throughout this process.
Expected technical difficulties and how we will overcome them: The technical
difficulties will include ensuring consistent measurements, as the data will be
collected by the investigators and clinical research staff.
2. Develop a computer algorithm that will distinguish "healthy" from "sick" Doppler
waveforms.
Waveform characteristics from the ED patients will be compared to previously collected
waveforms from normal volunteers. A computer algorithm will then be developed to identify
distinguishing features between these waveforms (independent of blood pressure). We will use
a similar power analysis as done by Holt et al.(11)
1. Algorithm Development: We will use MATLAB (The MathWorks, Inc) to analyze the Doppler
signals obtained from the hypotensive/shock patients and compare them to prior obtained
healthy patient data in order to identify unique wave characteristics of patients in
shock.
2. Filtering: Optimum filtering software will be designed and perfected by the PIs, as
required by the quantified audio piezo-electric signal, to determine most reliable and
accurate Doppler waveform.
Sample Size Calculation Previous studies have used a power analysis that determined 18
observation sets (a set being one intra-arterial BP measurement and one Doppler BP
measurement) to detect a difference of 10% (deemed clinically significant by investigators)
between intra-arterial and Doppler BP with a SD for difference of 7.8 mmHg and an alpha of
0.05 using a two-sided one-sample t-test.
A power analysis was not performed for this pilot study. A sample size of twenty adult
subjects (with Doppler recording during of < or = 5 minutes) was chosen to ensure sufficient
observations. Further statistical techniques to improve association will be implemented as
described in the initial prototype description.
