Updated July 27, 2016
Survival from sudden cardiac arrest is zero percent if external chest compressions are not performed. Since the 1950s, when Dr. Peter Safar first described the modern technique of pushing on the chest to create blood flow, researchers have worked to optimize manual compression depth and rate while trainers have trained millions of people worldwide in CPR.
Along with automated external defibrillators and basic airway management, CPR is considered a fundamental component of BLS in cardiac resuscitation.
Background
From the 1970s to the late 90s, much attention was given to ALS. It was thought that medications and ALS procedures such as intubation would help to increase survival rates.
However, in one study after another it became clear that these more complex and complicated techniques were not improving survival rates. It became increasingly obvious that effective BLS in the form of high quality chest compressions was crucial in resuscitation efforts.
In 2005, the American Heart Association recommended that the management of cardiac arrest revolved around minimally interrupted chest compressions of adequate depth and sufficient rate to adequate blood pressure in the cardiovascular system, while ensuring that full recoil off the chest was achieved to allow blood flow through the coronary arteries. In subsequent updates to the AHA CPR guidelines the emphasis on high-quality compressions continued.
Manual CPR
Historically, chest compressions have been delivered manually, with the rescuer kneeling upright next to the victim, using two outstretched arms placed over the sternum, and bending at the hips to create a downward force.
The rescuer returns back to an upright position, releasing all pressure off the chest. This “duty cycle” is repeated at a rate faster than 100 times per minute but slower than 120 times per minute, interrupted every 30 compressions to deliver a small volume of air to ventilate the lungs.
There are many challenges to achieving continuous, high-quality compressions. First, the rescuer must be of sufficient size and weight in order to generate adequate compressions. It is thought that late middle school children may be the minimum age to learn and deliver CPR.
Second, the training must be simple enough to acquire quickly and retain. Performing CPR is a task that is seldom practiced in real life by the lay public; even professional rescuers perform CPR at a much lower frequency than other procedures, such as measuring blood pressure or gaining intravenous access.
Given that mandatory retraining occurs usually on an annual or biannual basis, it becomes difficult to deliver compressions accurately.
Third, fatigue during CPR is a major factor. Studies show that the rescuer’s ability to deliver effective chest compressions decreases significantly in as little as a minute after initiation. It is for this reason that the AHA recommends that rescuers be rotated out of providing compressions every two minutes during a cardiac arrest.
Finally, trying to deliver effective manual chest compressions during patient extrication and transport is extremely difficult and dangerous for unrestrained EMS personnel who attempt to perform chest compressions in the patient care compartment of a moving ambulance. Maintaining body and arm position while in motion is impractical and can harm the rescuer.
Consistent, uninterrupted compressions
Given the challenges of trying to perform human-powered CPR, it’s no surprise that biotechnology has been working on mechanically-driven devices that tirelessly deliver accurate chest compressions in virtually any situation.
As early as the 1960s, the “Thumper” made by Michigan Instruments used an oxygen-powered piston on an adjustable arm to deliver compressions.
The ZOLL AutoPulse delivers chest compressions using a load-distributing band that is wrapped around the victim’s chest and tightened rhythmically by a battery-powered electrical motor.
Physio Control’s LUCAS is powered by compressed air. The LUCAS 2 is battery powered. Both devices compresses the chest with a piston in a more compact configuration.
The Resuscitation International ROSC-U Miniature Chest Compressor uses a chest compression component, attached to the patient’s chest, that is powered by a battery-control unit.
While the design of each device varies, the benefits to the resuscitation team are consistent, uninterrupted chest compressions. Mechanical chest compression devices can reduce the number of rescuers needed to perform CPR at a cardiac arrest, since the machines do not tire.
Properly applied and adjusted, the devices can deliver consistent, continuous compressions throughout the arrest phase. Studies have shown that using chest compression devices does promote coronary blood flow, higher coronary perfusion pressures and can increase the chances of return of spontaneous circulation (ROSC).
Given these findings, it would appear that chest compression devices are superior to providing manual CPR.
Yet large-scale scientific studies have not shown whether these devices are effective in improving the primary measurement of resuscitation success — survival to discharge from hospital.
Summary
At this point, the available evidence does not establish a preference for mechanical compression devices. We can expect researchers will continue to investigate the efficacy of the devices. Meanwhile EMS agencies should continue train, monitor and improve manual and mechanical chest compressions as part of a team approach to sudden cardiac arrest resuscitation.
Also keep in mind that a mechanical chest compression device is described in the 2015 AHA CPR guidelines as “a reasonable alternative to conventional CPR in specific settings where the delivery of high-quality manual compressions may be challenging or dangerous for the provider.” Those settings or situations are limited rescuers available to respond to a cardiac arrest call, prolonged CPR when guided by local protocols, CPR administered to patient who severely hypothermic and when a patient’s cardiac arrest cause and potential survivability may warrant transport in a moving ambulance.
