The Impedance Threshold Device, Why is it so Important to Use? -

The Impedance Threshold Device, Why is it so Important to Use?

Since the dawn of time, mankind has been tirelessly trying to find ways to prolong their earthly lives. Fables and legends, such as the Fountain of Youth, have been concocted to represent this longing. Modern medicine reflects that drive, today. Common maladies that would have leveled villages in centuries past are easily curable, if not completely avoidable through prophylactic inoculations. People who were, for all intents and purposes, dead have been and are still being brought back to life. Cardiac arrest survival is perhaps one of the topics receiving the most attention now. As a paramedic in a largely urban setting, I can attest to the obsession our community has to improve out-of-hospital cardiac arrest saves. So how do we improve already improved care? Several devices have been introduced to the realm of the resuscitation in recent years. Perhaps one of the most intriguing is the impedance threshold device (ITD).

So why is this device so important? Allow me to digress and briefly explain the “nuts and bolts” of the ITD. During the normal inspiratory pattern of a healthy person, the thorax expands causing a negative pressure to “suck in”, if you will, oxygen to the lungs and blood back to the heart. When a person deviates from their normal inspiratory pattern, the body requires ventilatory support continue its homeostatic rhythm. Whether it is a bag-valve mask, CPAP or BiPap machine, mouth to mouth, or a pocket-mask providing the ventilation, positive pressure is given to help the lungs expand. Whiles sometimes a necessary evil, positive pressure can have devastating effects on the heart. Overly aggressive positive pressure ventilation (PPV), simulates the effects of a figurative cardiac tamponade; the pressure “squeezes” heart and limits the amount of the blood that is allowed to enter or exit the heart. There are several negative effects that can happen as a result of this. Primarily, the heart is not oxygenated. It feels counterintuitive, but the less blood that is allowed to enter the heart, the less blood is able to enter to lungs where it becomes oxygenated, causing the body to become hypoxic. Secondly, when the heart is inhibited in its circulating ability, the brain is not properly perfused. Without the control center of the body being properly oxygenated, there is little to no chance for a patient to survive cardiac arrest with no long-term neurological deficits. The ITD claims to have solved this problem. According to the developers of the ResQPod, one of the most common ITDs in circulation, its main function is to reduce excessive positive pressure in the thorax while assisting ventilation. (2013) With more negative pressure in place, theoretically, there is significantly more oxygen flow to the lungs and blood flow to the heart and brain.

According to an article in the Journal of Emergency Medical Services (JEMS), the American Heart Association (AHA) has been endorsing the use of ITDs since 2005. (Elder, 2014) Despite the claim that the ResQPod had solved the problem of PPV, there were still quite a few skeptics, though. The ROC PRIMED study was conducted between 2007-2009; the findings of the study were disturbing to many. Despite the use of ITDs in witnessed cardiac arrest, there seemed to be no improvement in overall patient survival. (NIH, 2013) The authors of the ROC PRIMED study based their “success” criteria on a patient being discharged from a hospital following a witnessed out-of-hospital cardiac arrest with no long-term neurological deficit. The theory of the ITD was brilliant, so why did it fail? Critics of the study found several flaws in the manner in which ROC PRIMED was conducted. Breaking down every component of the arrest management, the critics found that those who did not survive received notably lower quality CPR from bystanders as well as pre-hospital emergency responders. (Elder, 2014) Secondly, providers were found to take lengthy or multiple attempts at placing advanced airways and overzealous bag-valve mask ventilations. (NIH, 2013) The lesson of the story, the use of ITDs in conjunction with early high quality chest compressions, defibrillation, and proper ventilation offers the best chance for survival in the witnessed cardiac arrest.

The ITD is a highly useful invention, and despite flawed studies, has been proven to be useful in cardiac arrest management. In addition to new technology, out-of-hospital staff is being encouraged to maintain standards of excellence while providing chest compressions, and not taking copious amounts of time off of the chest to simply place an advanced airway. While the ITD is not “necessary”, it is certainly beneficial in the art of pre-hospital resuscitation efforts.



Elder, J. (2015). CPR Quality and Impedance Threshold Device Effectiveness. Journal of Emergency Medical Services, 40(2). Retrieved from

Questions and Answers: ROC PRIMED. (2010). National Heart, Lung, and Blood Institute. Retrieved from