Just 5–15% of patients treated with standard CPR survive cardiac arrest, revealing a need for improved technique. To address this need, mechanical compression devices have become more prevalent and continue to evolve. Let’s take a look at the history of mechanical CPR devices and review their past and future in EMS.
Piston Chest Compression
These devices were first developed in the early ‘60s. Early research investigated variables of compression rate, duty cycle, and depth of compression, thus contributing to the on-going development of manual CPR techniques.(1)
Most piston compression devices use pneumatic power derived from compressed oxygen if there is an associated integrated ventilator, or from compressed medical air or oxygen if the device does not have a ventilator. The early Heart Lung Resuscitator (HLR) piston compression device had to be centered in the middle of the sternum by four straps.
The most widely used piston device is the Thumper, which has a built-in ventilator and is programmed to perform ventilations in the correct ratio of compressions to ventilations.(2)
The latest version of the Thumper, the Life-Stat (see Figure 1), is pneumatically powered but electronically controlled. It uses an arm that extends over the patient’s chest and an associated board provides a firm surface under the patient’s back.
Piston chest compression devices have been shown to be less damaging than manual CPR.(3,4) Trauma, such as rib fractures, is an occasional occurrence in CPR and a complication of this and other mechanical devices.
In the ’90s, this piston technique was further modified by the addition of an integral suction cup. Allowing for active return of the chest to the neutral, uncompressed position, it was an evolution that used both active chest compression and active chest decompression (ACD-CPR).
ACD-CPR research began with a report of an elderly man resuscitated with a bathroom plunger.(5) The system has evolved into the battery-operated LUCAS 2 device (see Figure 2), which uses an electrically actuated piston for chest compression and decompression and returns the chest to the neutral, uncompressed position.
In a series of 100 consecutive patients with witnessed cardiac arrest who were treated with the LUCAS 2 device less than 15 minutes after the 9-1-1 call, the 30-day survival was 25% if the patients were in ventricular fibrillation and 5% if they were in asystole.(6) If the device was placed greater than 15 minutes after the 9-1-1 call, there were no 30-day survivors.
The piston and active decompression devices are self-contained and do not require any disposable accessories or replacement expenses.
In the late ’70s to the early ’90s, another CPR device was under development as well. With vest CPR, a bladder-containing vest is placed circumferentially around part of the patient’s chest and cyclically inflated and deflated by an automated pneumatic system. Adherent defibrillation pads are placed on the chest before applying the vest to allow for defibrillation without having to remove the vest or interrupt CPR.
Vest CPR was designed to maximize the force applied to the chest during compression.(7,8) Force is distributed over the chest, which reduces local stresses on the chest wall and allows high forces to be applied safely. This distributed compression allows for large increases in intrathoracic pressure during chest compression, without the trauma inherent in applying force to a single point. It hasn’t been tested in large, clinical trials.
A more recent development is the load-distributing band (LDB). This battery-powered device uses a disposable electromechanically actuated band to distribute the compression load over the entire anterior chest at fixed intervals (see Figure 3). The concept is that circumferential pressure can be delivered around the thorax, and not just to the sternum, for forward flow to occur.
Recent trials showed improved hemodynamics, with coronary perfusion pressures above the level generally associated with improved survival, as well as improvement in survival to arrival at the emergency department when compared with manual CPR.(9,10)
One study, the ASPIRE trial, showed no difference between the manual CPR group (30%) and the LDB-CPR group (29%) at survival to four hours.(11) A Richmond, Va., trial, which also compared LDB-CPR with manual CPR, showed increased rates for achieving ROSC. Survival to hospital discharge was increased with the LDB (9.7% versus 2.9%).(12)
Minimal trauma attributed to the use of LDB-CPR was reported.
Mechanical CPR has a number of advantages over manual CPR, especially for use in EMS vehicles, and the research behind these evolving devices will guide field protocols in the immediate and long-term future. EMS agencies that are considering implementation of mechanical CPR devices must keep up to date with the latest technology and, more importantly, the science behind them.
Disclosure: The author has reported no conflicts of interest with the sponsor of this supplement.