5. Technology & mechanical assisted cardiopulmonary resuscitation – May 2015
Resuscitation of the patient in cardiac arrest is at the very core of all emergency clinical guidelines and first aid courses. There is no question that over the years there have been many different methods of providing resuscitation. This has involved methods of moving the patient’s arms around, pushing on the chest or back and trying to blow air into the lungs via mouth to mouth. It has evolved to the current ‘hard and fast’ chest compressions with deemphasised airway and ventilation methods. Paramedic focus has been on advanced airway, defibrillation, ventilation methods and post return of circulation resuscitation. However there has been a long history of mechanical methods employed that certainly still persist today.
Mechanical assist devices have been around for several decades and remain in current use. They seek to make a more even contact with the sternum but offer one arguable greater advantage over hands compressions. Modern versions have a suction cup that provides what is called active compression-decompression. The chest is not only pushed down but it is also pulled upward again to reduce the pressure in the chest and encourage blood return and flow. Unlike more complex mechanical options these are smaller, more portable and more mimic normal resuscitation.
In the early 1960s a device was developed by the founder of the company Michigan Instruments. This became known as the thumper and has evolved over the following decades whilst still operating on the same principle. It is basically a compression driven hydraulic piston that pushes down on the sternum when applied over the chest.
The LUCAS2 device operates on a not dissimilar basis by providing compression downward on the sternum during operation. This device is relatively easy to apply and minimally obtrusive on resuscitative efforts. The device was evaluated in a paper published in the Lancet in March 2015 showing it was able to provide comparable patient outcomes to manual compressions. The upside is the device does not tire and weaken like real people do though.
The autopulse is in current use by prehospital responders. Its mechanical band is attached to a half body board. It is wrapped around the patient’s chest with the patient supine on the board. When activated the device rhythmically contracts compressing the chest and releasing it again. The band is easy to apply and disposable after. They are proving reasonably effective at producing palpable pulses but are not yet overwhelmingly linked to improved outcomes. This may come with current trials. The only real down side is the device is somewhat heavy and bulky making it difficult to store in ambulances and a challenge to carry with other equipment. It also takes a short non CPR period to apply the device which is not desirable. The patient can be defibrillated with it in place.
Not all mechanical devices seek to perform the compressions for the rescuer. The vast majority of resuscitations are still performed by operators using their hands on the sternum. Only good quality chest compressions are associated with good outcomes and many efforts are made to ensure correct methods and rotation of fresh rescuers continues. To help with this many late model defibrillator devices now come with compression advice tools that provide real time feedback regarding compression quality of depth and rate. These can be used to help monitor resuscitation quality.
Finally, not all compression assist devices have sought to work on the outside of the chest. Internal or open cardiac massage has existed for many years as an in-hospital practice. During the late 1990s the Theracardia company introduced an invasive direct cardiac massage tool for pre-hospital use. A thoracotomy was made into the chest over the left ventricle and apex. This was widened using a blunt finger dissection and the heart actually touched by the operator. A device known as the MiD-CM (Minimally invasive direct cardiac massage) was pushed into the hole. What looked like a miniature umbrella was then opened that sat on the ventricle then the device quite literally pumped up and down. It never got past the experimental phase largely due to cost and not proving superior to manual methods but was certainly dramatic for the operator. It had the drawback of having to stop CPR to insert it which could take a couple of minutes. You could defibrillate through it. One noticeable curiosity was the heart felt like a rock each time intravenous adrenaline was administered!
Jeff Kenneally www.prehemt.com