What Is Mechanical CPR?

Mechanical cardiopulmonary resuscitation (mCPR) devices provide automated chest compressions to sudden cardiac arrest (SCA) victims. These devices are designed to achieve the return of spontaneous circulation (ROSC), just like manual CPR. However, while manual CPR is subject to human error and fatigue, mechanical CPR requires limited human interaction and can deliver consistent high-quality CPR on a continuous basis.

For this reason, mCPR devices are increasingly being used in conjunction with manual CPR. EMS teams have found this technology particularly useful since the automated, high-quality chest compressions give rescuers time to assess and treat other aspects of the patient’s condition. Additionally, it provides a safe and effective alternative to manual CPR in a moving ambulance.

In clinical studies, mCPR has been found to deliver outcomes similar to manual high-quality CPR, with the added benefit of reducing the stress on both EMS and care teams by automating a critical life support measure. 

The History of Mechanical CPR Devices

The first mechanical CPR devices were introduced in the 1960s and used a piston-based mechanism, also known as a thumper. The compressions were powered by electricity or compressed gas, while the compression rate and depth were controlled electronically.1 

mCPR device design advanced over time, incorporating load-distributing bands that increased intrathoracic pressure while improving patient comfort. The first of these devices was a specialized vest, known as Vest CPR. Compared to the piston devices of its time, Vest CPR was able to deliver better-quality CPR through its contracting load-distribution bands.1

Today, the modern, improved version of the Vest CPR is known as the ZOLL AutoPulse® Resuscitation System. AutoPulse improved upon the ease of use and setup of the Vest CPR. Since it is lightweight and stable, it helps EMS and other providers deliver high-quality CPR in scenarios where manual CPR is difficult — in small spaces or when patients need to be transported down a stairway or around corners. In fact, AutoPulse has been shown to reduce interruptions in compressions during transport by more than 85% when compared to manual CPR.2

How Modern Mechanical CPR Devices Work

There are two types of modern mCPR devices: piston-based devices and vest-based devices. Both serve a similar function — they perform automatic compressions at a fixed rate and depth. However, the two types of devices work quite differently.

Piston-based devices are typically powered by electricity, although some models use compressed oxygen. When in use, a specialized backboard is placed beneath the patient and the device is affixed to either side of the backboard, with the piston positioned above the end of the patient’s sternum. The piston compresses the patient’s chest and uses a suction cup to ensure active decompression and full recoil.1

The other type of modern mCPR device is a battery-powered vest device that uses an electric motor to pull a load-distributing band in a rhythmic motion, compressing the chest and improving perfusion3 to the heart and brain. These devices are lightweight and specially designed for portability, allowing rescuers to move the patient down stairways and through tight corridors without ceasing CPR. This device also supports the use of electrodes to help rescuers and members on the care team manually defibrillate the patient. To use a vest device, such as ZOLL AutoPulse, follow these steps.

  1. Perform high-quality CPR while the device is being prepared for use.
  2. Place the patient on a specialized, stable backboard. On the ZOLL AutoPulse®, make sure the yellow line is located directly below the patient’s armpit. Take care to minimize CPR interruptions during this process.
  3. Wrap the band (for the AutoPulse, use a LifeBand®) around the patient. Make sure the band is secure and not twisted. Make sure the yellow line on the LifeBand lines up with the yellow band on the backboard.
  4. Press the green start button to begin chest compression. The band will automatically size to the patient and compressions will begin.
  5. If necessary, set the compression rate and your compression-to-breath ratio. For the ZOLL AutoPulse, compressions will be delivered at a default rate of 80 compressions per minute at a 20% depth.

In practice, medical personnel should use mechanical CPR devices on a situational basis. While continuous compressions are absolutely essential to high-quality CPR, mCPR devices require that the care team ceases CPR for a few moments in order to apply the device to the patient. This is why purchasing a simple and effective mCPR device is crucial, and why proper training with your chosen device is even more important. If there are any significant delays or errors when setting up the device, it can impede your team’s ability to deliver high-quality CPR.

How Mechanical CPR Helps Deliver High-Quality CPR

High-quality CPR typically refers to a manual method of delivering chest compressions to an unresponsive individual in order to provide perfusion to critical organs — namely the heart and the brain — in order to facilitate the return of spontaneous circulation. It is a key determinant of patient survival and can double or even triple a patient’s chances of survival when delivered correctly. 4

CPR is considered high quality when it provides a chest compression fraction of greater than 80%, a compression rate of 100–120 per minute, and a compression depth of at least 2 inches in adults (or 1/3 of the anteroposterior dimensions of the thorax for infants or children). High-quality CPR also demands that rescuers do not excessively ventilate the patient.

However, it’s not easy to manually deliver high-quality CPR. Continuously compressing a patient’s chest can become physically exhausting for rescuers, and properly timing compressions can become mentally exhausting. Consequently, most rescuers can only deliver high-quality CPR for a few minutes at a time.

Usually it’s recommended to enlist the help of several people so rescuers can take shifts performing CPR but swapping out CPR providers means there is a short pause in CPR. Variations in skill and a limited number of rescuers can further complicate the issue. 

The requirements for achieving high-quality CPR and human limitations make it exceedingly difficult to achieve sustained delivery of high-quality CPR manually. One 2014 analysis of 9,136 out-of-hospital cardiac arrest patients found that only 45% received the recommended chest compression depth. When rescuers miss this or one of the other targets, they can unintentionally hinder a victim’s chance of survival.

This is where mechanical CPR devices can be beneficial. mCPR devices offer compressions at a consistent rate, depth, and fraction, and usually only require one interruption to apply the device to the patient. Once the device is applied, rescuers are free to work on other necessary interventions or begin transporting the patient to the hospital for more intensive care.

mCPR devices are especially helpful in conditions where CPR is difficult, if not impossible, to provide. For example, if a patient needs CPR for the entirety of their ambulance ride, the device can deliver prolonged CPR until they can be treated at the hospital. Even if a patient is being carried down a flight of stairs, rescuers can be confident that the device is providing consistent, high-quality chest compressions. mCPR devices are also used to provide high-quality CPR in situations like hypothermic cardiac arrest, in the angiography suite, during preparation for extracorporeal CPR, and in cases where few trained professionals are available to respond to an SCA victim.

Settings Where Mechanical CPR Is Used Today

Mechanical CPR can be used both inside of the hospital and outside of the hospital under certain circumstances. Let’s take a closer look at what studies have found regarding the use of mechanical CPR in various situations.

Out-of-Hospital

Many studies, trials, and analyses have been performed on pre-hospital use of mechanical CPR. Generally, these studies have either had a positive or mixed outlook on the use of mechanical CPR devices outside of the hospital.

  • A 2005 observational trial found that the ZOLL AutoPulse delivered a 10% higher chance of restoring spontaneous circulation in a pre-hospital setting (39% versus 29%).
  • A 2014 randomized trial found mechanical CPR to be slightly less effective than manual CPR. However, critics found that this study only used cases where high-quality manual CPR was performed perfectly for the duration of the cardiac arrest, which is exceedingly difficult in a real-life setting due to fatigue.
  • A 2015 systematic review of studies found there was no significant difference in neurological outcome or survival when comparing mechanical CPR to manual CPR.

Broadly speaking, many studies conclude that mechanical CPR and high-quality manual CPR are similarly effective. For this reason, while mCPR devices have a place outside of the hospital under specific conditions, they should not be used for every pre-hospital patient. Instead, opt for a mechanical CPR device only when a patient has no shockable rhythm and continuous manual CPR seems difficult to maintain. Under these conditions, rescuers can provide immediate, on-the-spot treatment and only leverage a device when it actively benefits the patient.

In-Hospital

While in-hospital studies on mCPR are not as exhaustive as pre-hospital studies, the results are favorable toward the use of mechanical CPR. More research is necessary to make any firm conclusions about the efficacy of mechanical CPR within the hospital.

  • A 1978 study with a piston device found that, when compared to manual CPR, mCPR was 4% more likely to help patients survive for an hour following cardiac arrest.
  • A 1993 study and a 2010 study both found that mechanical CPR was twice as likely to provide favorable outcomes within an in-hospital setting.
  • A 2016 meta-analysis found that mechanical CPR improved a patient’s odds of surviving for 30 days following cardiac arrest.

Given the evidence, it is reasonable to conclude that mechanical CPR devices have a place inside of the hospital, especially when a patient’s care team is preoccupied with other lifesaving measures or is otherwise unable to deliver high-quality CPR for an extended period of time. However, all hospitals should ensure that their staff are regularly trained on mCPR devices to ensure they are being used efficiently and effectively.

Conclusion

While mechanical CPR devices are not a total replacement for high-quality CPR, they play a key role in treating SCA victims under certain situations. For some scenarios, such as extended patient transport, they could be considered essential. As a result, mCPR devices are used by both EMS providers outside of the hospital and care teams inside of the hospital.

Mechanical CPR devices are an important part of responding to sudden cardiac arrest, so they should be acquired for both pre-hospital and in-hospital treatment of sudden cardiac arrest. However, to encourage the best possible care outcomes, mechanical CPR devices should be used in conjunction with high-quality CPR — not in its stead.

1 Cave DM, et al. Part 7: CPR Techniques and Devices. Circulation. 2010 Nov 2; 122:S720–S728.
2 Lyon RM, et al. Resuscitation. 2015;93:102–106.
3  Timerman S, et al. Resuscitation. 2004;61:3:273–280.
4 American Heart Association. CPR Facts & Stats, cpr.heart.org website, “https://cpr.heart.org/en/resources/cpr-facts-and-stats” Accessed Dec. 18, 2020.