Salvation or Salesmanship? A closer look at Impedance Threshold
Devices.
By Alan Perry
January 30, 2015
Cardiac arrest science and
outcomes have been changing at a rapid pace. New procedures and equipment have
radically changed the way we approach these cases and have significantly
improved the outcomes for victims in some locales. Techniques and equipment
that are proven to be effective require training for the pre-hospital provider
to apply them correctly and consistently. The Impedance Threshold Device (ITD)
is one such tool. Although the device is deceptively simple to use, its basic
function and correct application are not well understood by providers who have
simply been instructed when and where to use it. ITD’s are not universally
accepted as being effective or safe. Questions have been raised by independent
researchers and the Federal Government about the validity of the claims of the
manufactures supported research, implying that errors in study design, data
collection or bias may be involved. It would seem that the ancient caveat of
“buyer beware” still applies.
The basic selling point for these
devices is that in the setting of cardiac arrest, the use of the ITD improves
the return of blood the heart, thereby improving preload and stoke volume
induced by effective CPR while reducing ICP. The mechanics of this are fairly simple; once the ITD
is in place passive inspiration ceases due to the effective occlusion of the
airway by the ITD, When the chest is compressed effectively the pressure expels
blood from the heart and air from the lungs, when the chest recoils air cannot
return to the lungs, this produces negative pressure within the chest wall
which can assist blood in returning to the heart. In effect it sacrifices
respiration for circulation. This would seem to be quite effective in a
previously well oxygenated patient since the circulating blood presumably would
still be carrying enough oxygen to postpone permanent damage to organs.
Questions about the research on,
and use of ITD’s, are mounting and have merit. The Food and Drug Administration
(FDA), in a draft document published May 6, 2014 to its Circulatory System
Devices Advisory Panel posed questions about the research data, safety and
effectiveness of the device. Among these questions some fundamental problems
with the research were cited with the statement that the research does not
support the assertion of improved survival if used alone with standard
Cardiopulmonary resuscitation (CPR). The FDA’s Data Safety Monitoring Board
(DSMB) found that the studies were not effectively blinded, that they excluded
non-cardiac etiologies, and Emergency Medical Services (EMS) providers were not
blinded at all. Additionally, the document asserted that the development of
pulmonary edema was 30% more likely with ITD use, and that the manufactures
should consider labeling to further define which patients are appropriate
candidates.
Before we jump to any conclusions
about ITD’s, whether they are effective, or just the latest gadget we have been
sucked into buying, I think we should examine and consider what we know now. If
you think it through, considering the evidence, what we know about the
pathophysiology of cardiac arrest and the various co-morbidities, I think it
can still be an effective tool if we consider the totality of our patient’s
presentation and history and become more selective in the application of this
tool. In the setting of a witnessed cardiac arrest, presumably a myocardial infarction
or arrhythmia, the selection of the ITD to improve the effectiveness of CPR
would seem to be beneficial, provided effective compressions and airway
management are also present. Conversely, it would seem that a victim of cardiac
arrest secondary to some other event such as a drug overdose or pulmonary edema
which was primarily respiratory in nature would more likely benefit from
aggressive ventilation with effective CPR to correct the hypoxia that
precipitated the event.
Unfortunately, the ITD is not
currently marketed or deployed with these considerations. I believe manufactures
must be more diligent in conducting/supporting research that promotes patient
safety over sales. The government regulators must be more diligent in reviewing
the research and outcomes. Those responsible for applying new technology,
devices, practices, protocol and training within the local jurisdiction must do
their own research on them as well. We are taught from an early age to hear
both sides of an argument before reaching a decision, to beware of products
that sound to “too good to be true”. A thorough evaluation process that
involves the providers who will be using these devices as well as a training
program that imparts an appropriate level of understanding of the
pathophysiology and mechanics of the devices is a must.
A more refined set of
indications, contra-indications, and a better understanding of the
pathophysiology involved by providers, as well as better refined protocols
should led to more successes when using these devices and fewer complications
for patients. I offer this example for consideration:
To bring it home, we have to ask
ourselves about new things that are presented to us, evaluate them carefully
and validate any claims made by any manufacturer or salesman. Be aware that
shrewd companies may suppress negative information about their products or
services on the internet, so information from this source may be unreliable or
downright misleading.
Be safe and do your research,
Alan
References:
Food and Drug administration, Data Safety Monitoring Board website:
A trial of an impedance threshold device
http://com-emergency.sites.medinfo.ufl.edu/files/2013/02/A-Trial-of-an-Impedance-Threshold-Device.pdf
American Heart Association
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