Mechanical chest compression devices
Survival from sudden cardiac arrest depends on the early delivery of high quality cardiopulmonary resuscitation and early defibrillation. Research has shown that return of spontaneous circulation (ROSC) is increased where chest compression fraction can be maintained at 80% or greater, chest compression rate is maintained between 100-120 compressions per minute, chest compression depth is consistently achieved at between 5 to 6 cm in adults, and where full chest recoil is achieved by avoiding leaning on the chest wall.1 In cases of ventricular fibrillation, interruptions to chest compressions - including interruptions associated with defibrillation - have been shown to reduce the odds of ROSC.2 It therefore seems logical to use an automated chest compression device to ensure consistency of chest compressions (rate, depth and full recoil) while avoiding the need to pause compressions to defibrillate. Or does it?
In 2012 a systematic review of the literature was undertaken to identify evidence of effectiveness of one type of mechanical chest compression device. The researchers reported that the device improved physiological parameters in animals, but that human studies did not show an advantage in ROSC or survival. Studies included in this review were criticised for low quality of research methods, inadequate numbers enrolled, and poor reporting. The authors concluded that high quality randomised trials of this device were needed to reliably report outcomes.3
This call was answered when in 2014 when the results of a large multicentre study were published. In this study 2,589 adult patients with sudden cardiac arrest (excluding traumatic origin) were randomised to receive either mechanical chest compressions using the LUCAS device where compressions were uninterrupted during defibrillation, or manual CPR according to current (2010) resuscitation guidelines. The main outcome of interest was four-hour survival. Secondary outcomes were survival with good neurological outcome at defined time-points up to 6 months. There were 307 patients (23.6%) who survived to four hours in the mechanical CPR group, and 305 patients (23.7%) with the same end point in the manual CPR group. As you can probably guess, the difference between groups was not statistically significant (95% CI, -3.3% to 3.2%; P > .99). There was no significant difference in neurological outcome scores at any of the time points.4
In a more recent trial involving the use of the LUCAS-2 device within four UK ambulance services, the researchers used a cluster-randomised design to study survival at 30 days following cardiac arrest in adults. 4471 patients were enrolled (1652 assigned in the LUCAS-2 group, 2819 in the manual CPR control group). In the LUCAS-2 group 104 (6% of 1652 patients) survived to 30 days, and in the manual CPR group 193 patients (7% of 2819 patients) survived to 30 days. The adjusted odds ratio showed no significant difference between the groups (OR 0·86, 95% CI 0·64–1·15).5
Due to the lack of evidence of benefit arising from high-level studies, the Australian and New Zealand Committee on Resuscitation (ANZCOR) “suggests against the routine use of automated mechanical chest compression devices to replace manual chest compressions.”6 However, ANZCOR recognises that these devices are a “reasonable alternative to high-quality manual chest compressions in situations where sustained high-quality manual chest compressions are impractical or compromise provider safety.”6 In other words, where a decision is made to transport a victim of cardiac arrest while continuing CPR, these devices enable continuous and consistent chest compressions while allowing crew to be safely restrained during transport. While this may appear to be justification for the installation of this equipment in road and air ambulances, there are also some potential risks that need to be considered, as studies have identified risk of harm associated with the use of mechanical chest compression devices.
In a study designed to determine whether Team-focussed CPR improves survival with good neurological outcome in out-of-hospital cardiac arrest compared to standard CPR, Pearson and colleagues found that the use of a mechanical CPR device was associated with less likelihood of good neurological outcome.7 Further evidence of adverse outcomes is found in research undertaken by Youngquist and colleagues, which was designed to “compare functional survival (discharge cerebral performance category 1 or 2) among victims of out-of-hospital cardiac arrest (OHCA) who had resuscitation performed using mechanical chest compression devices vs. those using manual chest compressions.”8 This study found that mechanical chest compression device use was associated with lower rates of functional survival.8 In an earlier study that evaluated survival to four hours when patients were randomised to either CPR using a load-distributing band (LDB) circumferential chest compression device or standard manual chest compressions, the use of the LDB-CPR device was “associated with worse neurological outcomes and a trend toward worse survival than manual CPR.”9 A meta-analysis of research involving randomised and observational studies also failed to identify any improvements in survival or neurological outcomes.10
In summary, well designed studies have been unable to demonstrate a survival benefit when using a mechanical chest compression device. In addition, there is emerging evidence of adverse outcomes. High quality evidence must be used to assess risk and benefit to inform practice. This does not suggest that mechanical chest compression devices have no place in ambulances. For example, in settings where transport is required while continuing CPR – such as the early reperfusion trials for refractory cardiac arrest – manual chest compressions are unlikely to be either safe or effective in a moving vehicle. However, rigorous evaluation of new technologies must inform decisions regarding clinical benefit and the best use of limited health resources.
References 1. Meaney PA, Bobrow BJ, Mancini ME, et al. Cardiopulmonary resuscitation quality: Improving cardiac resuscitation outcomes both inside and outside the hospital. Circulation. 2013; 128: 417-35. 2. Brouwer TF, Walker RG, Chapman FW and Koster RW. Association between chest compression interruptions and clinical outcomes of ventricular fibrillation out-of-hospital cardiac arrest. Circulation. 2015; DOI 10.1161/circulationaha.115.014016. 3. Gates S, Smith JL, Ong GJ, Brace SJ and Perkins GD. Effectiveness of the LUCAS device for mechanical chest compression after cardiac arrest: systematic review of experimental, observational and animal studies. Heart. 2012; 98: 903-13. 4. Rubertsson S, Lindgren E, Smekal D, et al. Mechanical chest compressions and simultaneous defibrillation vs conventional cardiopulmonary resuscitation in out-of-hospital cardiac arrest: the LINC randomized trial. JAMA. 2014; 311: 53-61. 5. Perkins GD, Lall R, Quinn T, et al. Mechanical versus manual chest compression for out-of-hospital cardiac arrest (PARAMEDIC): a pragmatic, cluster randomised controlled trial. The Lancet. 2015; 38: 947-55. 6. Australian and New Zealand Committee on Resuscitation. ANZCOR Guideline 11.6 – Equipment and techniques in adult advanced life support. 2016. 7. Pearson DA, Darrell Nelson R, Monk L, et al. Comparison of team-focused CPR vs standard CPR in resuscitation from out-of-hospital cardiac arrest: Results from a statewide quality improvement initiative. Resuscitation. 2016; 105: 165-72. 8. Youngquist ST, Ockerse P, Hartsell S, Stratford C and Taillac P. Mechanical chest compression devices are associated with poor neurological survival in a statewide registry: A propensity score analysis. Resuscitation. 2016; 106: 102-7. 9. Hallstrom A, Rea TD, Sayre MR and et al. Manual chest compression vs use of an automated chest compression device during resuscitation following out-of-hospital cardiac arrest: A randomized trial. JAMA. 2006; 295: 2620-8. 10. Bonnes JL, Brouwer MA, Navarese EP, et al. Manual cardiopulmonary resuscitation versus CPR including a mechanical chest compression device in out-of-hospital cardiac arrest: a comprehensive meta-analysis from randomized and observational studies. Ann Emerg Med. 2016; 67: 349-60.