Cardiac & Resuscitation, Equipment & Gear, Exclusives

Mechanical CPR Devices: Where is the Science?

A mechanical CPR device in a Magen David Adom mobile intensive care unit in Israel. Photo by Oren Wacht.

High-quality CPR is one of the few interventions proven to enhance neurologically intact survival from cardiac arrest. The components of high-quality CPR include compression fraction (the amount of time compressions are delivered divided by the total time of the resuscitation attempt), compression depth, compression rate, recoil (allowing full thoracic expansion after each compression) and Peri-shock pauses (pauses in compressions before and after defibrillation).

The American Heart Association (AHA) Guidelines for Emergency Cardiac Care (ECC) stress the importance of rotating rescuers (changing the person delivering compressions) every two minutes. Delivering high-quality chest compressions requires substantial physical and mental effort, especially if resuscitation continues for more than a few minutes. In the prehospital setting, a limited number of providers further adds to the stress and physical effort.

In order to reduce provider’s physical and mental fatigue and to simplify management of CPR, mechanical compression devices (mCPR) seem like an ideal solution for providing high quality compressions. This article discusses the scientific evidence regarding routine use of mCPR and suggests guidelines for adoption of mCPR devices by EMS systems.

MCPR devices are not new; they were introduced in the 1960s using a piston-based mechanism. Over the next few decades, developments like vest-CPR and load distribution bands were invented.1

Although not recommended by the AHA for routine use while performing CPR (Class 2b), mCPR devices have become more common amongst EMS providers in the last few years. This observation raises the question: Why does any medical device become popular? The reasons may include: the natural urge to use new and improved technology, the desire for better patient outcomes, ease of use for the healthcare providers and industry driven sales. While performing CPR in a moving ambulance is not usually recommended, crew safety may dictate use of mCPR devices.

In order to evaluate the possible advantages of mCPR devices, a basic understanding of the goals of CPR is needed. In the prehospital setting, providers are generally unaware of the outcomes of patients they resuscitate and deliver to a hospital. Since the definition of successful CPR is not ROSC (return of spontaneous circulation), but rather neurologically intact survival to discharge from a hospital (released with a Cerebral Performance Category of 1 or 2), then prehospital providers often remain unaware of their successes. It’s also important to note that most patients with ROSC die after presentation to the hospital.

Historically, some interventions shown to increase rates of ROSC also decrease rates of neurologically intact survival (high dose epinephrine, for example). As a consequence, using prehospital ROSC as an outcomes measure fails to encompass long-term outcomes of field interventions.2

The definition of successful resuscitation is not ROSC, but neurologically intact survival to hospital discharge. We can’t know this in the field.

The two most important interventions in cardiac arrest care are high-quality CPR with minimal interruptions and early defibrillation.

The 2015 AHA CPR guidelines recommended a compression rate of 100-120 per minute at a depth of 2-to-2.4 inches, enabling full recoil and minimizing pauses. Managing a patient in cardiac arrest is a stressful event even for experienced providers. One method by which rescuers reduce cognitive stress and fatigue is by using mCPR devices.

In theory, mCPR devices perform compressions at a fixed rate and depth; the machine does not tire while performing “perfect” compressions. Using mCPR devices ensures continuous “high quality compressions” without the need to continually rotate the person doing compressions. Theoretically it’s the perfect solution, but what does the science show us?

In 2016, Buckler DG et al. analyzed 80,681 cases of cardiac arrest and found that survival to hospital discharge and neurologically favorable survival were greater in patients not receiving mCPR (9.5% versus 5.6%, P<0.0001 for neurologically favorable survival).1

An earlier methodical review and meta-analysis examined five random clinical studies involving over 10,000 patients who suffered cardiac arrest outside of the hospital (OHCA) (Gates 2015). The researchers concluded that there is no difference in ROSC, survival to discharge or survival with good neurological outcomes when using mCPR devices compared to manual CPR.

In their review, Ong ME et al.3 and Newberry R et al.4 found that there is insufficient evidence to support or negate the use of mechanical CPR devices for cardiac arrest outside of the hospital or during ambulance transport. There are indeed low-quality testimonials about mechanical CPR improving consistency and reducing interference with chest compressions, but there is no evidence that mechanical CPR devices improve survival. We should consider the possibility that the opposite is true, and these devices might impair neurological outcome.

Gates S et al.5 examined the use of the mCPR LUCAS-2 compared to manual CPR among 4,471 patients who suffered out of hospital cardiac arrest. They randomized to EMS treatment using either type of CPR. The results did not demonstrate an improvement in 30-day survival using the LUCAS-2 compared to manual compressions.

In another methodical review of studies evaluating the effectiveness of mechanical chest compressions, Gate S et al.6 included randomized controlled trials and random cluster trials comparing mechanical chest compression (using an AutoPulse device, LUCAS-2, or LUCAS device) with manual chest compressions for adult patients after OHCA. The results did not find mechanical chest compression devices preferable to manual chest compressions when used during CPR following OHCA.

So, when does science suggest we do use mCPR devices?

Where quality compressions are not possible under specific circumstances (limited rescuer availability, prolonged CPR, hypothermic cardiac arrest, during ambulance transport, in the angiography suite, during preparation for extracorporeal CPR), the use of mechanical devices may be a reasonable strategy. When using mCPR devices, clinicians must ensure that the device is deployed in the correct position and with minimal interruption of chest compressions.7,8,9

Why aren’t we seeing better outcomes with mCPR devices? Why aren’t more patients surviving neurologically intact when we use the machines that deliver perfect CPR?

The most reasonable explanation is that rescuers underestimate the time needed to place the device on the patient, thereby leading to substantial pauses in CPR. There is evidence that team training prior to the incident can reduce the pause required for utilizing the machine.

Some case studies and post-mortem investigations suggest mCPR devices cause physical injuries such as rib cage damage, lung and cardiac contusions that are detrimental to survival.10, 11

Another known phenomenon with some mCPR devices is their tendency to “shift” the focus of their compression to the abdomen during prolonged use. 

Many prehospital providers are also familiar with the phenomenon of hemoptysis after a mCPR device is deployed. Although described in case studies only, blood in the airway may be indicative of damage to internal organs and possibly affect ventilations.

When transporting a patient in cardiac arrest may be indicated:

While the AHA guidelines suggest using a termination of Resuscitation (TOR) rule to avoid unnecessary transports, as that can be dangerous and costly, some very specific indications exist for transporting patients in cardiac arrest.12 Using an mCPR device during transport is safer for the crew and does not interrupt compressions. Two relatively new indication for transporting patients as part of a “treatment bundle” are:

1) PCI for refractory VF: A patient in VF who is not responding to prehospital treatment (defibrillation, CPR, drugs) and remains in VF. PCI in-hospital can potentially reverse refractory VF. This sort of intervention requires a systemwide approach with well-choreographed synchronization between EMS and hospitals. In this case, mCPR is used both in transport and in hospital during PCI.13

2) Transporting a patient with a potentially reversible cause of death to a facility capable of initiating ECMO (extracorporeal membrane oxygenation). ECMO (which can be established prehospital using a specialized team and equipment) is highly technical and expensive but can potentially benefit a select group of patients when combined with targeted temperature management.14

Conclusions

MCPR devices are currently being used by many EMS agencies.

In the absence of published evidence on effectiveness, a decision to utilize mechanical CPR can be affected by system considerations such as number of rescuers and/or long evacuation times. The cost of mCPR devices is also a consideration, especially if system-wide adoption is desired. In EMS systems that allow or encourage transport with CPR in progress could enhance crew safety by utilizing mCPR. Lastly, mCPR devices assure compression depth and rate, as well as control pauses. Alternatively, CPR feedback may have capability to provide similar assurances.

EMS organizations considering the integration of mechanical CPR devices must remain up to date on the latest technology and, most important, their underlying science.

Like any technology, it is important to understand the advantages and the disadvantages. Thinking of the best possible outcomes for our patients, mCPR seems appropriate in very select cases, where their benefits outweighs potential for harm.

One suggested protocol developed by the national EMS system in Israel (Magen David Adom) recommends use of mCPR devices only in three distinct situations:

  1. Transporting a patient for organ donation, as a means of keeping organs viable
  2. Transporting a patient with refractory VF to a dedicated cardiac catheterization lab that can perform PCI during delivery of mechanical compressions
  3. When there are limited personnel on scene, deploying mCPR after a few rounds of manual CPR, keeping in mind that most neurologically intact cardiac arrest survivors achieved ROSC in the first few minutes

References

1. Association of Mechanical Cardiopulmonary Resuscitation Device Use With Cardiac Arrest Outcomes – A Population-Based Study Using the CARES Registry (Cardiac Arrest Registry to Enhance Survival) David G. Buckler , Rita V. Burke , Maryam Y. Naim , Andrew MacPherson , Richard N. Bradley , Benjamin S. Abella , and Joseph W. Rossano. Circulation. 2016;134:2131–2133.

2. Mechanical CPR devices compared to manual CPR during out-of-hospital cardiac arrest and ambulance transport: a systematic review. Ong ME1, Mackey KE, Zhang ZC, Tanaka H, Ma MH, Swor R, Shin SD. Scand J Trauma Resusc Emerg Med. 2012 Jun; 18;20:39.

3. Olasveengen TM, Wik L, Sunde K, et al. Outcome when adrenaline (epinephrine) was actually given vs. not given – post hoc analysis of a randomized clinical trial. Resuscitation 2012; 83:327-32.

4. No Benefit in Neurologic Outcomes of Survivors of Out-of-Hospital Cardiac Arrest with Mechanical Compression Device. Newberry R, Redman T, Ross E, Ely R, Saidler C, Arana A, Wampler D, Miramontes D. Prehosp Emerg Care. 2018 May-Jun;22(3):338-344.

5. Prehospital randomised assessment of a mechanical compression device in out-of-hospital cardiac arrest (PARAMEDIC): a pragmatic, cluster randomised trial and economic evaluation. Gates S , Lall R, Quinn T, Deakin CD, Cooke MW , Horton J, Lamb SE, Slowther AM, Woollard M, Carson A, Smyth M, Wilson K, Parcell G, Rosser A, Whitfield R, Williams A, Jones R, Pocock H, Brock N, Black JJ, Wright J, Han K, Shaw G, Blair L, Marti J, Hulme C, McCabe C, Nikolova S, Ferreira Z, Perkins GD. Health Technol Assess. 2017 Mar;21(11):1-176.

6. Mechanical chest compression for out of hospital cardiac arrest: Systematic review and meta-analysis. Gates S, Quinn T, Deakin CD, Blair L, Couper K, Perkins GD. Resuscitation. 2015 Sep;94:91-7.

7. Mechanical CPR: Who? When? How? Kurtis Poole,Keith Couper, Michael A. Smyth, Joyce Yeung, and Gavin D. Perkins. Crit Care. 2018; 22: 140.

8. Mechanical versus manual chest compressions for cardiac arrest. Wang PL, Brooks SC. Cochrane Database Syst Rev. 2018 Aug 20;8:CD007260.

9. Mechanical devices for chest compression: to use or not to use? Couper K, Smyth M, Perkins GD. Curr Opin Crit Care. 2015 Jun;21(3):188-94.

10.The LUCAS 2 chest compression device is not always efficient: an echographic confirmation Giraud R, Siegenthaler N, Schussler O, Kalangos A, Müller H, Bendjelid K, Banfi C. Ann Emerg Med. 2015 Jan;65(1):23-6.

11.Unexpected collateral impact after out of hospital resuscitation using LUCAS system. Shahinian JH, Quitt J, Wiese M3, Eckstein F, Reuthebuch O. J Cardiothorac Surg. 2017 Sep 7;12(1):81.

12. 2015 American Heart Association Guidelines Update for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Part 3: Ethical issues.

13. Management of Refractory Ventricular Fibrillation. Ravi S, Nichol G. JACC Basic Transl Sci. 2017 Jun; 2(3): 254–257.

14. Refractory cardiac arrest treated with mechanical CPR, hypothermia, ECMO and early reperfusion (the CHEER trial). Stub D, Stephen B, Pellegrino et al.