Cardiac & Resuscitation, Patient Care

CPR Quality and Impedance Threshold Device Effectiveness

Issue 2 and Volume 40.

High-quality CPR is one of the hottest topics in resuscitation. But like many therapies or approaches in prehospital care, it’s hardly the only thing impacting survival. It’s important for us to take a systems-based approach to addressing cardiac arrest, with a focus on improving not only CPR quality, but also perfusion during CPR. Such an approach features the seamless interaction of several elements, including:

>> Minimizing peri-shock pauses;1
>> Compressing at the right rate and depth;
>> Conducting robust quality assurance reviews;
>> Evaluating the use of therapeutic hypothermia in prehospital therapy;2 and
>> Use of perfusion enhancing devices.

Recently, the role of the impedance threshold device (ITD) in EMS systems has also entered the debate. Now, emerging data and experience from our EMS systems indicates the ITD does improve survival.3,4

The key: It must be implemented as part of a system of care that includes high-quality CPR. This approach is essential to moving from high-quality to high-perfusion CPR.

High-Quality CPR

Research has shown high-quality CPR improves outcomes. Most recently, an analysis of the Resuscitation Outcomes Consortium (ROC) database showed a direct correlation between chest compression rates and survival.3 Based on these and other data, the American Heart Association (AHA) recently issued a consensus statement outlining the metrics of optimal CPR performance.5 These include:

>> Compressing the chest at a rate of 100 to 120 compressions per minute;
>> Minimizing interruptions in chest compressions with a targeted chest compression fraction of > 80%;
>> Achieving a chest compression depth of ≥ 50 mm (for adults);
>> Allowing full recoil of the chest wall with no residual leaning; and
>> Avoiding excessive ventilation (rate < 12 breaths per minute with minimal chest rise).

It’s critical for EMS agencies and communities to begin to measure and report their success in meeting these criteria, because they are the basis of a robust cardiac arrest quality assurance program.

Using ITDs to Improve Perfusion

The ITD has been recommended in the AHA Guidelines since 2005 and there’s substantial data to support its use to enhance perfusion during CPR.6

At least 25 human and animal studies have shown improvements in hemodynamics (e.g., increased vital organ blood flow, lowered intracranial pressure, improved coronary and cerebral pressures) and improved survival from cardiac arrest when an ITD is used.

However, the ITD’s role in resuscitation has been the topic of debate since the ROC PRIMED Study. This large, prospective, randomized trial of more than 8,000 subjects compared the use of an active (functional) and sham (non-functioning) ITD and showed no improvement in functional survival.7

The neutral results from this trial were puzzling given the body of evidence that had preceded it. Now, a new analysis of this data is helping us understand how to use the ITD effectively to improve outcomes.

Data has emerged to help us better understand the impact CPR quality has on the ITD’s efficacy. Cheskes and colleagues published data from the ROC PRIMED Study indicating there was a wide range of adherence to CPR quality.1 A legitimate question then is: What effect did poor CPR quality have on the effectiveness analysis of the ITD in the ROC PRIMED Study?

Yannopoulos and colleagues hypothesized that CPR quality would directly impact outcomes with the ITD, so they analyzed data on patients who received high-quality CPR (defined as compression rate of 80–120/min, depth of 4–6 cm, chest compression fraction of > 50%) that was consistent with AHA Guidelines at the time of the study. A total of 848 patients in the active ITD group and 827 patients in the sham ITD group received documented CPR according to these parameters.

The recently published analysis shows that when high-quality CPR was delivered, the active ITD improved survival to hospital discharge with good neurologic function by 75%.4 Figure 1,seen above, depicts functional survival to hospital discharge in patients receiving an active or sham ITD with various CPR quality indicators.

Because of how the ITD works, CPR quality (e.g., rate, depth, pauses) appears to have an almost dose-related effect on hemodynamics and survival. The ITD can be likened to a mechanical drug that is powered by chest wall recoil. It’s designed to enhance the negative intrathoracic pressure (vacuum) that’s responsible for filling the heart during the decompression phase and increasing preload. Thus, the ITD’s “dosing” is essentially the quality of CPR being performed during its use. If the chest isn’t allowed to recoil, device performance is hampered. If the rescuer hyperventilates the patient, excessive positive pressures will negate its effect. Finally, chest compressions that are too fast often result in inadequate depth and shortened or inadequate filling times. The recent sub-analysis of the ROC PRIMED Study showed that administering the ITD at the proper “dose” (i.e. with high-quality CPR) dramatically improves its effectiveness.

An impedance threshold device (ITD) is used to enhance perfusion during CPR. Photo Julianne Goulding Macie


Using a Systems-Based Approach to Improve Survival

Data from the ROC PRIMED Study makes the challenge for EMS systems clear: The performance of high-quality CPR is critical for improving survival, especially when an ITD is used. New data also confirms that when EMS systems perform high-quality CPR, adding an ITD can help improve perfusion and survival. The ITD, however, isn’t a silver bullet, just as a single drug is typically not the cure for most types of cancer. Many agencies have adopted systems-based approaches to out-of-hospital cardiac arrest (OHCA) and are showing impressive survival rates.

Our systems use similar approaches to achieving high-perfusion CPR:

1. Adjuncts and methods to improve CPR quality, including:

>> A “pit crew” approach, which has been widely implemented by EMS systems to better choreograph resuscitations and limit rescuer fatigue;
>> Use of metronomes and feedback devices to achieve the correct compression rate, depth and fraction; and
>> Transition to an automated CPR device when possible, and preferred if transporting patients with ongoing CPR.

2. Use of an ITD to enhance perfusion, including:

>> Ensuring appropriate compression rates; and
>> Activation of the timing lights to guide ventilations.

3. Other elements of a systems-based approach, including:

>> Less emphasis on endotracheal intubation during initial resuscitation;
>> Focus on community awareness, bystander CPR education and AED placement;
>> Implementation of strategies to reduce response times;
>> Dispatcher-assisted CPR and performance review;
>> Transport to hospitals that offer specialized care (e.g. therapeutic hypothermia) and 24/7 interventional cardiology for resuscitated patients; and
>> Monitoring and tracking data for continuous quality improvement.

This approach has been successful for our systems. Self-reported data from the 2013 Cardiac Arrest Registry to Enhance Survival (CARES) shows the average overall survival to hospital discharge rate for all rhythms in our three EMS systems is 14.6% (range 9.7–18.8%), and for patients who meet the Utstein criteria survival is 50.6% (range 44–55.6%)—far above the reported 10.6% and 38%, respectively, of high-performing EMS systems reporting CARES data.8 But we’re not unique in our recipe for success. Studies by Aufderheide, Hinchey and other colleagues have shown that use of similar systems-based approaches produce increases in survival to hospital discharge.9–11

Putting It All Together

Our results show we can move the needle on survival from OHCA. Our focus on high-quality CPR and enhancing perfusion through adoption of a systems-based approach has demonstrated increased survival rates. Emerging data and practical experience from additional EMS systems are helping us to understand factors that make a difference. This prescriptive approach to enhancing multiple factors in cardiac arrest management and providing feedback demonstrates that it’s within our power to ensure that more sudden cardiac arrest patients leave the hospital alive.


1.  Cheskes S, Schmicker RH, Verbeek PR, et al. The impact of peri-shock pause on survival from out-of-hospital shockable cardiac arrest during the Resuscitation Outcomes Consortium PRIMED trial. Resuscitation. 2014;85(3):336–342.
2.  Nielsen N, Hovdenes J, Nilsson F, et al. Outcome, timing and adverse events in therapeutic hypothermia after out-of-hospital cardiac arrest. Acta Anaesthesiol Scand. 2009;53(7):926–934.
3.  Idris AH, Guffey D, Aufderheide TP, et al. Relationship between chest compression rates and outcomes from cardiac arrest. Circulation. 2012;125(24):3004–3012.
4.  Yannopoulos et al. The effect of CPR quality: a potential confounder of CPR clinical trials. Circulation. 2014.
5.  Meaney PA, Bobrow BJ, Mancini ME, et al. Cardiopulmonary resuscitation quality: improving cardiac resuscitation outcomes both inside and outside the hospital: a consensus statement from the American Heart Association. Circulation. 2013;128(4):417–435.
6.  Cave DM, Gazmuri RJ, Otto CW, et al. Part 7: CPR techniques and devices: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2010;122(18 Suppl 3):S722.
7.  Aufderheide TP, Nichol G, Rea TD, et al. A trial of an impedance threshold device in out-of-hospital cardiac arrest. N Engl J Med. 2011;365(9):798–806.
8.  Cardiac Arrest Registry to Enhance Survival (CARES);
9.  Aufderheide TP, Yannopoulos D, Lick CJ, et al. Implementing the 2005 American Heart Association Guidelines improves outcomes after out-of-hospital cardiac arrest. Heart Rhythm. 2010;7(10):1357–1362.
10. Hinchey PR, Myers JB, Lewis R, et al. Improved out-of-hospital cardiac arrest survival after the sequential implementation of the 2005 AHA guidelines for compressions, ventilations and induced hypothermia: the Wake County experience. Ann Emerg Med. 2010;56(4):348–357.
11. Lick CJ, Aufderheide TP, Niskanen RA, et al. Take Heart America: A comprehensive, community-wide, systems-based approach to the treatment of cardiac arrest. Crit Care Med. 2011;39(1):26–33.
12. Matsuura T, McKnite S, Metzger A, et al. An impedance threshold device combined with an automated active compression decompression CPR device (LUCAS) improves the chances for survival in pigs in cardiac arrest. Circulation. 2008;118:S1449–1450.
13. Yannopoulos D, Matsuura T, Wayne M, et al. Evaluation of the hemodynamic synergy between an impedance threshold device and the LUCAS 2 automated CPR device in a pig model of cardiac arrest. Prehosp Emerg Care. 2014;18(1):131.
14. Saussy JM, Elder JE, Flores CA, et al. Abstract 256: Optimization of cardiopulmonary resuscitation with an impedance threshold device, automated compression cardiopulmonary resuscitation and post-resuscitation in-the-field hypothermia improves short-term outcomes following cardiac arrest. Circulation. 2010;122(21_MeetingAbstracts):A256.
15. Escott MEA, Jenks SP, Traynor KM, et al. External cardiac bypass? A case series: hemodynamics of LUCAS Device plus an ITD in cardiac arrest. Prehosp Emerg Care. 2014;18(1):156.
16. Satterlee PA, Boland LL, Johnson PJ, et al. Implementation of a mechanical chest compression device as standard equipment in a large metropolitan ambulance service. J Emerg Med. 2013;45(4):562–569.


Wayne Schneider and the team that performed life-saving CPR. Photo courtesy Advanced Circulatory

Sidebar – Case Presentation: One of Our Greatest Success Stories

Wayne Schneider was 56 years old and a seemingly healthy veteran paramedic for Hennepin County EMS in Minneapolis. In December 2012 he was on a call, taking care of a patient who had overdosed. After loading the patient in the ambulance, Wayne’s partner found him in the front seat of the ambulance, slumped over in cardiac arrest. Manual CPR was started and Wayne’s partner radioed for help. When the second ambulance and crew arrived, they began automated CPR using the LUCAS 2.

Despite being in v fib, perfusion was so good they had difficulty intubating, with Wayne thrashing his arms about during CPR. After drug therapy and numerous shocks, however, Wayne remained in refractory v fib throughout transport to Hennepin County Medical Center, a Level 1 trauma center that also offers therapeutic hypothermia and a 24/7 cardiac catheterization lab.

Upon arrival at the ED, providers used rapid sequence intubation to secure Wayne’s airway and placed a ResQPOD ITD. Additional medications and defibrillations were administered, and high-quality automated CPR was continued for a total of 68 minutes until ROSC was finally achieved.

Wayne was brought immediately to the cath lab where a “widow-maker” occlusion in his left anterior descending coronary artery was opened. He was placed on an intra-aortic balloon pump, then into a medically induced coma for therapeutic cooling. Two days later Wayne awoke and was extubated. He made a full neurologic recovery and returned to work teaching CPR as he’s done for 20 years to thousands of students.

Photo coutesy Advanced Circulator


Sidebar – The ITD & Automated CPR: Making Good CPR Better

There’s no doubt about it—saving lives is hard work! And maintaining high-quality manual CPR for long durations can be challenging. Because of this, many EMS agencies begin with manual CPR but transition to automated CPR devices for extended resuscitations or transport. But as we all know, even the best CPR provides limited blood flow, whether it’s manual or automated. This is due, in part, to the fact that an open airway allows air to enter the chest and wipes out the vacuum we rely on to fill the heart. If we correct that inefficiency by using an ITD with automated CPR, what does the data show?

Animal data looking at the ITD in combination with the LUCAS device (which contains a suction cup to assist with chest wall recoil) is quite supportive of the apparent synergy. In two swine models, investigators found that end tidal carbon dioxide, systolic and diastolic blood pressures, and coronary and cerebral perfusion pressures were all significantly higher, and that ROSC was easier to achieve in animals when an active ITD was added to LUCAS CPR.12,13

Many EMS systems have reported both improved survival and increased levels of consciousness during CPR with the automated CPR and ITD combination. Two human studies, one reporting a 71% increase in stable ROSC rates, and the other reporting near-normal perfusion in patients in pulseless electrical activity and asystole, have been published.14,15 The St. Paul-Minneapolis metropolitan area has perhaps the largest concentration of hospitals and EMS systems utilizing an ITD in combination with over 400 automated CPR devices.16 2013 data from CARES for the Twin Cities shows that the rate of survival to hospital discharge in patients from all rhythms is 13%, and for patients in witnessed v fib is 48%.8