Friday, January 30, 2015

Salvation or Salesmanship?

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

American Heart Association

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