The use of Mechanical CPR Devices in a pre-hospital setting: A review of the literature with recommendations for clinical utilization
By Peter Thorpe PgDip, Director of Strategic Program Development, Medical Programs British Columbia Emergency Health Services (BCEHS)
Mechanical cardio pulmonary resuscitation (CPR) has promised to improve outcomes for patients in both hospital and out of hospital setting by improving the quality and consistency of CPR, essential in improving survival rates from cardiac arrest. The efficacy of mechanical CPR has been evidenced in laboratory conditions and staged testing. Results showed more consistent refractory periods, more consistent depth and rate, and when used in a moving vehicle potentially remove the need for paramedics to ride unrestrained. While it is likely that mechanical CPR devices have a role to play in pre-hospital medicine where manual CPR is not possible, difficult or as a bridge to advanced therapies, there are still questions on their role other than in very specific situations and in relation to patient outcomes.
However, despite questions about the clinical effectiveness of mechanical CPR devices many EMS systems and First Responder organizations are deploying these expensive items to an increasing number of ambulances and responder units for general use. In some cases, more effective and evidenced-informed interventions1 may have not been implemented e.g. Telephone CPR, Public Accessible Defibrillator databases, crowd sourced bystander CPR applications and public CPR learning events.
This article looks at the evidence for implementation of a mechanical chest compression device in an EMS System, reviewing literature for both the PhysioControl LUCAS Chest Compression System2 and the ZOLL AutoPulse Resuscitation System3 mechanical CPR devices and is intended to start a conversation. However, an underlying question is that as EMS, either health-based or public safety-based, continues to grow and as we adopt new technologies, do we need to be more rigorous in assessing the clinical effectiveness of the devices we deploy?
To investigate the use of mechanical CPR here in the Canadian province of British Columbia we wanted to understand in more detail the evidence supporting mechanical CPR devices and in particular the LUCAS and AutoPulse devices. We wanted to develop internal BCEHS4 recommendations on the use of mechanical CPR devices as well as outlining areas where we felt more research is needed to support their wider use in pre-hospital medicine.
Many articles use different acronyms for mechanical and manual CPR as well as different terms for AutoPulse devices and LUCAS devices.
For consistency I have used the full wording for mechanical CPR and manual CPR. For AutoPulse I have used iA-CPR (as used in the CIRC trial) and L-CPR for LUCAS devices. Other terms used in various papers include ‘LDB’ or Load Distributing Band that references the action of the AutoPulse or Piston Driven ‘PD’ that references the action of the LUCAS device.
Unless otherwise stated all the studies referenced relate to human trials using mechanical CPR. The intent of this article is not to draw a direct comparison between the AutoPulse or LUCAS devices or to single out a particular device for criticism.
MARKETING OF MEDICAL DEVICES
Firstly, let’s discuss the marketing associated with medical devices. Manufacturers of medical devices and pharmaceuticals have spent many years honing their skills in selling products to medical professionals and not always to the patient’s good, as we have seen in the current opioid crisis. There is no suggestion of harm being caused on the scale of the current opioid crisis by the use of mechanical CPR devices, but a question: Are we as experienced in dealing with manufacturers as we think we are?
Both PhysioControl (LUCAS) and ZOLL (AutoPulse) as manufacturers have made easily-accessible materials available describing their products and how they can impact outcomes. Obviously, I must state openly for balance that my limited summary below of this information is biased as I have focused on contradictions in these materials. Some of the research quoted does offer support for the use of both LUCAS and AutoPulse in the management of out-of-hospital cardiac arrest. There is also no suggestion that any researchers involved in these trials were not transparent about their industry funding, contracts or positions within the manufacturer’s organizations. However, in my view there is currently no clear high-quality definitive evidence to suggest that mechanical CPR is superior to, or more effective than, manual CPR in a pre-hospital setting in these papers.
The LUCAS Bibliography5 summarises the PARAMEDIC6 trial telling us ‘…there was no evidence of improvement in 30-day survival with LUCAS 2 device compared with manual compressions, but it was noted that actual use of the LUCAS device in the LUCAS group was low’. However, it misses the finding: ‘The trial was unable to show any superiority of mechanical CPR and highlights the difficulties in training and implementation in a real-world EMS setting’.
The ZOLL website7 for AutoPulse makes a number of statements around efficacy of iA-CPR. The website includes the following statement: ‘Multiple trials confirm the AutoPulse is superior to manual CPR when it comes to increasing a patient’s odds of achieving return of spontaneous circulation (ROSC)’.
Of the papers referenced that support this, Steinmetz et al8 investigated the implementation of the 2005 European Resuscitation Council guidelines9. In this investigation data including AutoPulse use was only found in the second arm of the trial after the implementation of the new guidelines were made. In discussion investigators say: ‘We do not know what role the chest compression device played in relation to overall improvement in survival as the apparatus was only associated with improved ROSC at admission but a significantly worse 30 day survival rate. The chest compression device was only used in 77/419 of the cardiac arrests resuscitated. From this we can hardly claim that the AutoPulse was fully implemented in our unit’. Of those studies that did demonstrate improved outcomes for mechanical CPR included in this section of the Zoll website caveats included – ‘not statistically significant’10, ‘…research is needed to further define the value of LDB in resuscitation’11 or ‘…may improve the overall likelihood of sustained ROSC…’12.
The reason I highlight these cases, from both LUCAS and AutoPulse literature, is to highlight the need to evaluate the Class of Recommendations (i.e. strength) and the Level of Evidence (i.e. quality) of evidence we are given on interventions.
Evaluating clinical research using, for example, the AHA framework13 allows consideration of the Class of Recommendations. Language may include words such as ‘indicated/useful/effective/bene cial’ which are strong recommendations or ‘may/might be considered’ which are classed as weak recommendations. For Level of Evidence; Level A is high quality evidence from more than one RCT, while Level C-LD includes randomized or non-randomized observational or registry studies with limitations of design or execution and a lower level of evidence.
Our challenge is to evaluate all available evidence, in a framework that allows us to synthesis findings into a risk-based, decision-making process around the introduction of new technologies, procedures or medications. The point I want to make is this: Are we fully investigating the effectiveness of equipment being deployed or are we willing victims of marketing collateral?
Early Trials: Earlier porcine trials of the mechanical CPR devices14,15, conclude that they contributed to better circulation in resuscitation from Ventricular Fibrillation than manual CPR. A more recent study reported in the Scandinavian Journal of Trauma, Resuscitation and Emergency Medicine16 also supported this finding using a load-distributing band that improved ventilation and hemodynamics in a porcine model of prolonged arrest. This study found that the use of LDB ‘…significantly improve the hemodynamics and respiratory parameters during resuscitation, dramatically producing greater passive ventilation, which can improve gas exchange during CPR…’
CPR quality during ambulance transport: A series case study17 on the quality of CPR in Europe (n176) found that chest compressions in out-of-hospital cardiac arrest (OHCA) were not delivered consistently and most were too shallow. ECG analysis and defibrillation accounted for only small parts of these gaps. A similar study comparing the LUCAS device and manual CPR using manikins undertook 16 simulated eight-minute ambulance transports18. In the transports using manual CPR there were variations in quality not seen in those involving the LUCAS device. The trial noted limitations but hypothesised that the LUCAS device was a reliable alternative to manual CPR in transport situations, stating that further clinical studies were required to inform this hypothesis.
Paramedic Safety: Provision of manual CPR in a moving vehicle is difficult and increases the risk of paramedic injury; however, there was limited research found in this area. In Hong Kong a study19 found that 60% of responding paramedics (n318) complained of discomfort when delivering CPR (in any setting), with a sub-cohort associating CPR to back injuries. The use of mechanical CPR devices for prolonged periods of CPR may reduce the risk of musculoskeletal injuries to paramedics and other emergency responders.
Patient Harm: Investigation into harm caused by L-CPR devices20 found that in patients with unsuccessful CPR following OHCA there was no difference in the incidence of sternal fractures compared to patients receiving manual CPR. While the study noted a higher rate of rib fracture, no injury sustained was found to be fatal. Paradis NA et al21. in an abstract for the California AutoPulse Quality Assurance Registry published in Circulation (2009) comments: ‘Adverse events are only rarely reported by EMS personnel and do appear more common in patients treated with the iA-CPR device’. Couper et al22. in their review of mechanical CPR suggest that there is no overall difference in injury rates caused by chest compressions in both the CIRC23 and LINC25 trials, but there are differences they say in the injury patterns. In all of these papers it is stressed that the instance of potential injury was low.
Patient Outcomes: Findings of a large US population-based study (n80861) into survival from OHCA was published in a CARES Research Letter24 (all types of mechanical CPR devices). It concluded that ‘mechanical CPR for routine cardiac arrest care was associated with worse outcomes’. Outcomes were based on survival rates (11.3% manual CPR, 7% mechanical CPR) and favourable neurological outcome survival (9.5% manual CPR, 5.6% mechanical CPR). It noted that data on the time of arrest, time of first CPR and timing of interventions were not reliably reported, including any delays in time to first de defibrillation. Importantly it also highlighted variations in the use of m-CPR across agencies. The median use was 43.9% (21.7% in >75% of responses and 37.7% in <25% of responses). Similar outcomes for both survival and neurological outcomes were evidenced where the use of mechanical CPR exceeded 50% of responses.
The LINC Randomized Trial25, funded by PhysioControl, was a multi-centre clinical trial (n2589) comparing manual CPR and LUCAS device with measures at 4hrs and secondary end points of survival at 6months and CPC score. During the trial changes were made to the resuscitation protocol for patients receiving mechanical CPR with an initial shock prior to analysis and 3min CPR cycles. A noticeable difference in study cohorts was the time to first defibrillation with the mechanical CPR cohort 90 seconds later than the manual CPR cohort. This trial concluded that mechanical CPR using the LUCAS device can be delivered without major complications with no difference in 4hr survival between groups. Researchers stated that mechanical CPR ‘…did not result in improved outcomes compared with manual chest compressions’ and that further investigation of the amended resuscitation protocol was needed.
The CIRC23 trial with centres in the US and Europe, compared manual CPR to mechanical CPR using AutoPulse. In the introduction the researchers acknowledged that mechanical CPR would never fully replace manual CPR however they state that ‘…there was a need for another randomized clinical trial comparing manual and integrated mechanical CPR, where a patient receives manual compressions while the mechanical device is deployed’. The trial enrolled n4753 patients with 49.6% (n2099) receiving CPR using AutoPulse and 50.4% (n2132) receiving manual CPR. The findings across all three measurements: sustained ROSC to ED (iA-CPR 28.6% vs manual CPR 32.3%); 24 hour survival (iA-CPR 21.8% vs manual CPR 25.0%) and to hospital discharge (iA-CPR 9.4% vs manual CPR 11%) met the criteria for equivalence (odds adjusted ration of 1.06).
The trial protocol, developed by ZOLL with the principal investigator, used a complicated double triangle statistical test design which in the author’s own words ‘…is unfamiliar to many in this field’. With this statistical model their conclusion that ‘…compared to high quality manual CPR, iA-CPR resulted
in statistically equivalent survival to hospital discharge’ is supported in their findings.
The inclusion of the CIRC23 trial in a subsequent meta-analysis, Gates et al26. has raised questions around the design, including missing neurological data at discharge and the exclusion of some data from one centre. The authors of this meta-analysis go as far as to suggest that ‘…the conclusion of “equivalence” in this situation is questionable’.
Wyer27 in commentary of Bonnes et al28. meta-analysis of randomized and observational studies reminds clinicians and researchers of well-established patterns of effect going on to say: ‘In OHCA, mechanical compression devices and other failed interventions…may restore cardiac function in the field and increase hospital admissions (and the cost of care) but are unlikely to improve patient survival to hospital discharge’. He suggests that: ‘Clinicians should look beyond new drugs and devices, focus on the basics of effective CPR, and await well-controlled clinical trials framed to test basic assumptions.
Neurological Outcomes: Most of the primary end points of trials for mechanical CPR have focused on ROSC. Arguments for this include variations in post-arrest treatments in hospital and post-resuscitative care. These trials have posited that this is the most appropriate measure of effectiveness for these devices, even when the period of ROSC is as low as one minute. Other trials have been poor at collecting neurological data with CIRC23 missing 27% of data on this outcome at discharge in part due to the study design.
Newberry et al30. explored this important measure and points to some interesting observations. Their retrospective observational study compared outcomes of n3,469 patients over a 36month period. While their data showed mechanical CPR as being associated with poor neurological outcomes, once adjusted by logistical regression for confounding variables the outcomes were similar. They suggest that advanced airway management and medications may be the root cause of the poorer outcomes with higher rates of endotracheal intubation and epinephrine use with mechanical CPR devices. They suggest that current resuscitation protocols are developed around manual CPR and the greater efficiency of mechanical CPR may, for example, increase the toxicity of epinephrine. They suggest that due to these poor neurological outcomes: ‘The continued use of mechanical CPR devices should be limited until further investigation better defines the optimal medication dosages and airway management when mechanical CPR devices are utilized’.
Early trials concluded improved consistency with the use of mechanical CPR and improved blood ow during CPR. These factors have not been disproved and subsequent trials have confirmed that these benefits are realistic. However, the advantages they should give during resuscitation have not been clearly evidenced in subsequent clinical trials and particularly in patient-oriented outcomes.
The risk of harm during transport for OHCA patients and paramedics alike has been mitigated significantly as protocols for discontinuation of resuscitation have been adopted. This has reduced the numbers of patients being transported to emergency departments with ongoing CPR in transit. However, for the small number of cardiac arrest patients with a treatable cause being transported this risk still exists. In addition, more at risk cardiac patients31,32, are now being transported to specialized cardiac services by EMS based air critical care programs. With manual CPR being impossible in aircraft, cardiac arrest protocols for pre-flight application are now common.
While there is some evidence that mechanical CPR devices have caused injury to patients there does not appear to be a body of evidence to call on to support this as a significant factor in their use. In fact, in many cases manual CPR is given prior to the application of mechanical CPR and those injuries may have resulted from the manual CPR. Most of the research in this area, Couper22 suggests, relies on autopsy and radiography which are not systematically collected or reported. The low level of evidence in this area coupled with the suggestion that there is a potential risk for some patients though cannot be ignored when considering wide spread deployment of these devices.
The CARES Research Letter24 suggested potential adverse outcomes with low rates of mechanical CPR device application. However, survival and neurological outcomes for patients where the application
of mechanical CPR devices was high was consistent with manual CPR, suggesting potential issues with training and confidence in their use. Many trials have raised the need for a comprehensive and ongoing training package to be linked to the use of mechanical CPR. CIRC23 with its long lead in period and training program reported favourable outcomes. PARAMEDIC6 trial reported concerns around training and maintenance of competency in the use of mechanical CPR devices. During this trial (n4471) 40% of the mechanical CPR cohort did not receive mechanical CPR. Within this group 15% did not receive mechanical CPR ‘because of difficulties inherent with implementation of new equipment and the training and quality issues’, the conclusion recommended that ‘research should look to de ne the optimum method and frequency of such training’.
Targeted rather than general deployment could help with skills retention for practitioners, higher usage rates and allow for easy identification of any remedial training requirement.
The LINC Randomized Trial25 demonstrated comparable outcomes but involved changes to resuscitation protocols for those receiving mechanical CPR with the authors suggesting further investigation into those changes. Newberry30 also raises the question of the use of standard resuscitation protocols for mechanical CPR rather than amended protocols that may be better suited to their use. While this
is supposition it may in some part explain why survival rates from mechanical CPR do not consistently match or better cases where manual CPR is provided.
The review found no body of empirical evidence demonstrating improved survival rates associated with the use of mechanical CPR. However, there are occasions when manual CPR is ineffective and mechanical CPR has a place, including as a bridge to advanced therapies. Despite results not confirming the superiority of mechanical over manual CPR many researchers suggest exactly this conclusion while stressing the need for comprehensive training regimes. Taking these factors in to account we developed three internal BCEHS recommendations:
- Mechanical CPR devices may be used in the following circumstances: transfers with medical/hospital teams; approved clinical trials; high angle patient rescue; confined space retrieval or transport e.g. airvac; hypothermic cardiac arrest retrieval and transport.
High quality manual CPR would be difficult in all these circumstances. The risk of re-arrest in some cases may be high and the pre-placement of a mechanical CPR device could be considered in confined spaces such as aircraft. Mechanical CPR devices may have been placed correctly by hospital teams prior to arrest or during advanced therapies e.g. ECPR and removing them would cause patient harm or the cessation of those therapies.
- If already applied by an appropriately trained person and the number of responders does not allow for an appropriate rotation for HQ-CPR then the device can remain in situ until enough responders are available. In addition, if the patient is transported then it may be left in situ to reduce the risks associated with CPR in a moving vehicle.
One explanation for poorer survivability rates with mechanical CPR devices are delays in treatment while devices are applied. Removing them therefore may also cause further delays in treatment. Misplacement of devices or technical issues with them may raise the risk of injury to patients and delay other treatments, therefore requiring trained staff to travel with the patient. The numbers of patients being transported with CPR enroute is low and often this is with treatable causes e.g. post-trauma, immersion or hypothermic arrest. If CPR is indicated for treatment and a device has been applied unless high quality CPR is possible it should ideally not be removed.
- The term ‘appropriately trained person’ includes: First Responders dispatched by BCEHS who have advised of their intent to use; hospital medical teams; members of the BC Search and Rescue Association (BCSARA) and Canadian Coast Guard and/or Canadian Armed Forces Medical Teams, if trained and used by them.
Currently BCEHS is a partner in the CanROC ECPR (ECMO)33 study for refractory out-of-hospital cardiac arrest with the study protocol including the pre-hospital placement of LUCAS device on the study population. It may be possible depending on evidence from that trial that at a later stage a cohort of BCEHS Specialist Paramedics or Advanced Care Paramedics may join this list of appropriately trained persons.
Many studies and meta-analyses have recognised that outcomes with mechanical CPR especially survival to discharge, neurological status and in some cases ROSC alone, do not either match or surpass results where high quality manual CPR is possible and provided. However, it’s clear that mechanical CPR has its place where manual CPR is not possible or difficult, or as a bridge to advanced therapies.
The question though remains why mechanical CPR with its advantages does not perform as well as manual CPR with all its inherent challenges? The fact that one of the biggest trials, CIRC23 of a mechanical CPR device involved a complex statistical analysis to evidence only equivalency adds to the concerns regarding the empirical evidence supporting mechanical CPR.
Evidence suggests that use of mechanical CPR does not lead to improved survival rates and neurological outcomes, but have we truly compared consistent measures in these trials? Wyer27 reminds us that we need to understand patterns of effect. Is there bias in the belief that the use of mechanical CPR leads to worse outcomes because it’s not proven otherwise, or is the reality that the use of mechanical CPR restores cardiac output temporarily for patients that previously would have treatment terminated on scene? Meta-analysis of data relating to in-field discontinuation of resuscitation between mechanical CPR and manual CPR may also inform the discussion around differences in survival rates.
Has statistical analysis truly compensated for confounding variables when looking at survival rates between manual CPR and mechanical CPR? The reality may be that 30day survival rates are no worse or even better for mechanical CPR than when every cardiac arrest patient was transported to hospital with no in-field discontinuation of resuscitation.
Newberry et al.30 also questions treatment guidelines and protocols used for resuscitation with mechanical CPR devices as they are based on the research and physiological response to manual CPR. LINC25 addressed this with changes to the resuscitation protocol for those patients being treated with the LUCAS device, suggesting that further understanding of the impact of these changes was required.
New evidence may come from clinical trials looking at outcomes for OHCA patients with resuscitation protocols around airway management, pharmacological protocols and discontinuation of resuscitation designed specifically for use with mechanical CPR devices. These may answer the question of why mechanical CPR does not appear to perform as well as manual CPR.
It is obvious that mechanical CPR technology should not be dismissed or ignored for OHCA. The value of mechanical CPR devices in the field to support ongoing hospital therapies is recognised, many post-arrest patients are being transported by air medical transport to centres of care and no doubt there will be improvements in design and training for their use.
LOOKING TO THE FUTURE?
It is said that one should always end on a positive note. A 2009 French34 study took three groups of French Red Cross First aiders (n80) who were unfamiliar with AutoPulse and with minimal awareness (one group had two illustrations, one had four illustrations and the final one had a five minute video and familiarisation time with the device) and asked them to place on a manikin. With this small amount of training the last group (video and handling) were able to place the device with no errors in placement in 19 seconds and the time to first compression was 48 seconds.
In an environment where we coach CPR and guide the use of an AED on the phone, is it unreasonable to expect to see the use of mechanical CPR devices by the general public and for them be as common as AED’s or re extinguishers in buildings once we have the answer to the questions posed here?
To discuss this article or provide feedback, please email Peter at: [email protected]