Michael Levy, MD, FACEP, FACP, Diplomate EMS Medicine
Mechanical CPR (mCPR) has been around for decades, and the current devices are a sophisticated evolution of the earlier efforts. Although there was initial enthusiasm that the load distributing band (LDB) technology (Autopulse® Zoll Corporation) could provide a new type of CPR with superior perfusion,1 the best science suggests that LDBs provide equivalent outcomes to manual CPR in out of hospital cardiac arrest. The most recent large trial evaluating the LDB mCPR, the CIRC trial,2 showed that in the prehospital environment the device was equivalent to world class manual CPR.
The piston-type technology, such as employed by the LUCAS device, (Physio-Control Inc., Lund, Sweden) presents a more straightforward mimic of traditional CPR but includes a suction cup that may assist the chest relaxation and monitors to ensure safety and reliability. Two large out-of-hospital trials showed parity with manual CPR,3,4 although they had notable limitations, such as comparing optimal mCPR to usual manual CPR, use of 3-minute CPR cycles, and defibrillation during mCPR without checking the rhythm.3
How do these studies showing lack of superiority of mCPR unequivocally support the use of mCPR in EMS and hospitals? These studies demonstrate that, at worst, mCPR is equivalent to manual CPR, and therefore, we should consider situations in which manual CPR is difficult to perform. Manual CPR in moving ambulances, helicopters and small medevac jets is dangerous and suboptimal.
As we consider the impact of the large trials on decisions on mCPR, attention should be given to whether CPR performed within most hospitals is truly at the same caliber as that by EMS. Even if provider performance were similar, in-hospital CPR is still limited by being performed on a compressible surface at an awkward height whereas EMS performs CPR on the ground. (“Code Boards” lead to minimal improvement in the effectiveness of CPR performed on a hospital bed.)5,6 It is therefore conceivable that mechanical CPR is advantageous relative to manual CPR in a hospital setting.
Minimizing pauses in CPR is associated with improved outcomes. mCPR allows for minimal pauses: flip a switch off, check a rhythm, flip a switch on and back to CPR. The large trials did not report objectively on pauses related to application of the device. We performed an application time study, showing the before and after effects on our times by analyzing our process and carefully monitoring our times by measuring the change in impedance signal morphology in our cardiac arrest reviews.7,8
The best outcomes from cardiac arrest occur with witnessed ventricular fibrillation and pulseless ventricular tachycardia. These rhythms typically respond quickly to defibrillation and minimal CPR is needed. mCPR is used in prolonged arrests, those with a lower likelihood of survival. mCPR in these cases will be equivalent to manual CPR which, and both, in many cases, will be unfortunately futile. We must continue to treat these arrests for the occasional success, but they will over-represent failures to resuscitate compared to the “easy” cardiac arrests.
The expense of the devices is noted, especially considering the price of the device as well as initial and recurrent training, mandatory for a successful deployment. For EMS services, even if the devices are desirable, the cost may be prohibitive. For most hospitals, in contrast, the cost of placing devices in the cath lab, the ED and with a code team, is equivalent to rounding error in the scheme of hospital finance. The argument of the expense and excess use of resources could be juxtaposed against the resources we throw at “futile” trauma resuscitations.
How dangerous is mayhem and confusion? Looking back at your last code, it was no doubt distracting that you had to monitor the quality of compressions while you simultaneously considered how to resuscitate the patient. If you have used mCPR then you know that it imparts a certain serenity to the code as you no longer have the hubbub associated with manual CPR.
An important use of mCPR is as a bridge to PCI for suitable patients who have refractory VF likely due to acute coronary occlusion. This is best done with mCPR while going directly to cath without ROSC. Some institutions have the ability to transition to LV assist devices or ECMO to provide perfusion while treating the underlying coronary occlusion. There are many examples of successful outcomes in this situation,9-14 including a prospective, nonrandomized trial.15
Both manual and mCPR are associated with injuries to the bony thorax, and all CPR begins with manual CPR. Notably, bad CPR never causes injury. Since publication of the ECC 2010 guidelines, injuries have increased overall.16 There is an increased risk of presternal hematoma with LUCAS and LDB, but no evidence of potentially fatal injuries in post mortem findings. Anecdotes of thoracic spine injuries have alternative explanations of manual CPR, rescuing from drowning, severe osteoporosis, or the like. In my experience with the LUCAS device, it is imperative that the tower is perpendicular to the chest wall and remains properly positioned on the sternum. If the device were to be positioned over the lower sternum or upper abdomen, injury could occur.
When I was younger I used to mow the lawn pushing a manual, reel-type mower (a web search may be necessary for some readers). It was ultimately effective, but it was laborious. A power mower was considered an expensive luxury that would undoubtedly (per my worried mother) cut off my fingers or toes. Years later, we ended up getting such a device and found it more reliably cut the lawn, was easier to use and did not result in random amputations when used according to instructions and common sense. It did require routine maintenance and respect for its potential dangers. I am fairly confident that if a trial were performed, it would have shown no difference in outcome with these expensive, dangerous devices compared to manual technique.
Machines are engineered to exceed human capacity for predictable repetitive tasks involving manual labor. Whereas humans will tire and introduce random errors in repetitive motor activity, a well-engineered machine never will. The compressions associated with high performance CPR are tasks highly suited for machines and poorly matched for human function. While well-trained humans can in fact provide very good CPR, most do not. Furthermore, most systems of care do not provide the type of training and feedback required for us to achieve this level of perfection. Mechanical compression is NOT required for the treatment of all cardiac arrests, nor will it lead to improved outcomes in the majority of events. It is, however, a vital tool that can be used to improve our delivery of care in time critical dire emergencies.
Disclaimer: The NALES trial of which I was a contributor was supported by Jolife, distributor at that time of LUCAS and our system received six of the LUCAS-1 devices at the time. We employ LUCAS devices in our EMS system of which I am the medical director but receive no industry support for this. Our system used LDB in the late 2000s and moved away from them. I have received a consulting fee from Physio-Control® for clinical work on monitor defibrillator technology.