a b s t r a c t

Introduction: European Resuscitation Council as well as American Heart Association guidelines for cardiopulmo- nary resuscitation (CPR) stress the importance of uninterrupted and effective Chest compressions . manual CPR decreases in quality of CCs over time because of fatigue which impacts outcome. We report the first study with the Lifeline ARM automated CC device for providing uninterrupted CCs.

Methods: Seventy-eight paramedics participated in this randomized, crossover, manikin trial. We compared the fraction of effective CCs between manual CPR and automated CPR using the ARM. Results: Using the ARM during resuscitation resulted in a higher percentage of effective CCs (100/min [interquar- tile range, 99-100]) compared with manual CCs (43/min [interquartile range, 39-46]; P b .001). The number of effective CCs decreased less over time with the ARM (P b .001), more often reached the required depth of 5 cm (97% vs 63%, P b .001), and more often reached the recommended CC rate (P b .001). The median tidal volume was higher and hands-off time was lower when using the ARM. Conclusion: Mechanical CCs in our study adhere more closely to current guidelines than manual CCs. The Lifeline ARM provides more effective CCs, more ventilation time and minute volume, less hands-off time, and less de- crease in effective CCs over time compared with manual Basic Life Support and might therefore impact outcome.

(C) 2016

Introduction

Each year, there are approximately 420 000 out-of-hospital cardiac arrests occurring in the United States and 275 000 in Europe [1]. Current European Resuscitation Council (ERC) as well as American Heart Associ- ation (AHA) guidelines for cardiopulmonary resuscitation (CPR) stress the importance of uninterrupted Chest compressions [2-5]. Sur- vival after cardiac arrest depends on prompt and good quality CPR [6,7]. Those guidelines recommend that rescuers should push hard to a depth of at least 5 cm at a rate of at least 100 compression per minute (but not more than 120 per minute), allow full recoil of the chest be- tween compressions, and minimalize interruptions in CCs with a com- pression to ventilation ratio of 30:2 [2,3]. We know that relatively brief interruptions in CCs of even 4 seconds lead to reduced myocardial perfusion and survival [8]. However, manual CCs, at best, result in a car- diac output of approximately 20%-39% of normal, and their effectiveness

? Conflict of interest: The authors report no conflict of interest. Institutional funding only.

* Corresponding author at: Department of Internal Medicine I, Intensive Care Unit, Med- ical University of Vienna, 1090 Vienna, Austria.

E-mail address: [email protected] (O. Robak).

is limited by rescuers’ endurance [9-11]. Several studies have demon- strated a decrease in the quality of CCs over time during manual CPR [12,13].

Mechanical CC devices have been developed to avoid this decrease in CC quality and to supplement manual CCs. Manual CCs remain the standard of care for the treatment of cardiac arrest, but mechanical pis- ton devices may be a reasonable alternative for use by properly trained personnel [14]. However, it is a known problem that CC devices can slip during compressions and cause harm [15-17] although it has to be men- tioned that manual CCs also cause injuries [18]. Newly developed auto- mated CC devices are therefore needed to further improve CC quality. One of those is the Lifeline ARM (Defibtech, Guilford, CT) CC device. The main idea behind the development of automated CC devices is that a mechanical device provides CCs more effectively and consistently than humans because of the lack of fatigue in the course of CPR. More- over, when using mechanical CC devices, the patient can be defibrillated during ongoing CCs, reducing the hands-off time which is known to be an independent predictor of survival in out-of-hospital sudden cardiac arrests [19,20]. Paramedics who do not need to provide CCs manually are able to concentrate on other aspects of patient care [21]. Data from clinical observational studies suggested that mechanical CCs might be superior to manual CCs in sudden cardiac arrest [22,23]. The ARM has

http://dx.doi.org/10.1016/j.ajem.2016.10.012

0735-6757/(C) 2016

been developed to comply with the latest ERC guidelines to minimize hands-off time and maximize efficiency of CCs. The Lifeline ARM de- livers compressions using a state-of-the-art removable compression module which contains a software-controlled compression piston, a simple user interface, a power source, and a motor drive ensuring effi- cient and smooth operation as the piston moves up and down. Com- pared with the LUCAS CC device, it is easier to assemble and lighter, fewer steps are required for setup, and it is robust against disturbances. A compressions-with-breaths protocol facilitates ventilation during CPR. Because this device has not been tested for its performance so far, the aim of the study was to compare mechanical with the ARM Lifeline and manual CCs during CPR.

Methods

Study design and participants

This study was designed as a follow-up to a small pilot study [24] as a randomized, crossover, manikin trial and approved by the Institutional Review Board of the International Institute of Rescue Research and Edu- cation (approval no. 15.01.2016.13). The study was conducted in accor- dance with declaration of Helsinki in February 2016.

Seventy-eight paramedics participated in this trial. Inclusion criteria comprised professionally active paramedics, less than 5 years of experi- ence in Emergency Medical Service (EMS) or emergency department, more than 20 clinical CPRs, and no previous experience with mechanical CC devices. Exclusion criteria comprised wrist or low back diseases and pregnancy. All participants were verbally informed about the intention of the present study and gave their written informed consent to take part in this trial.

Description of the device

The Lifeline ARM (Defibtech, Guilford, CT; Fig. 1) is an automated, portable, battery- or AC-powered device that provides mechanical CCs on adult patients in cardiac arrest. The Lifeline ARM consists of a back- board, a frame, and a removable compression module (Fig. 2). The back- board is placed under the patient to provide a solid base for the device. The frame is placed over the patient and snaps into the backboard with self-locking latches. The compression module mounts on the frame and

Fig. 1. Lifeline ARM: the mechanical CC system.

contains the user interface, a replaceable battery pack, and the piston drive used to generate the CCs. Compressions are initiated using a sim- ple 3-step operational sequence: the unit is turned on, the piston height is adjusted for the patient’s chest size, and the compression button is pushed. The device ensures effective CPR with compression depth (at least 2 in/5 cm) and rate (at least 100/min) as recommended in current AHA/ERC guidelines. The weight of the device is 7.1 kg. The design of the Lifeline ARM affords portability, speedy deployment, compressions with or without rescue breaths, event capture, and serviceability.

Conduct

Before starting the test, all participants were instructed by anesthe- siologist on ARM and conventional manual CPR according to the current guidelines for CPR by the ERC (2015) [5]. Following the lecture, partici- pants were given 10 minutes to practice standard basic life support (BLS) with manual CC and BLS with mechanical CCs on a manikin to make sure that they were familiar with their proper use. The same anes- thesiologist was present during the practice section to give advice to participants.

After the training session, each participant performed the identical scenario in a randomized order, one with ARM and once with manual

CC. Each participant performed CPR on a SimMan 3G training manikin (Laerdal, Stavanger, Norway). The Research Randomizer program was used (www.researchrandomizer.org) to randomize participants to 2 groups and determine the order of participants and order of CC method. The first group performed standard manual CCs, and the second group performed CCs using the ARM device (Fig. 2). Participants used bag- valve-mask ventilation at a ratio of 30:2 (30 CCs were interrupted to im- mediately perform 2 ventilations) according to current guidelines. Par- ticipants performed 8 minutes of CPR according to the ERC guidelines. We chose this interval because the mean response time for the EMS teams in Poland in urban areas is 8 minutes. After completing each pro- cedure, participants took a 60-minute break before performing CCs using the other method.

Outcome measures

The primary outcome measure was the percentage of effective CCs, which were defined as CCs performed with the correct depth 50-60 mm, the correct compression rate 100-120 per minute, the correct hand position, and complete decompression [5]. Secondary outcome measures were mean depth, rate of CCs, pressure point, complete pressure-release CCs, incorrect hand position, and incomplete decom- pressions. ventilatory parameters such as tidal volume, ventilation rate, minute volume, and number of gastric inflations were also record- ed. Moreover, we recorded the absolute hands-off time, defined as the sum of all periods during which no hand was placed on the chest minUS time used for ventilation (ventilation time). The above parame- ters of CC effectiveness were monitored using software provided with the training manikin used. During CPR, the participants were not pro- vided any information recorded by the manikin monitoring system and were guided only by their own experience. In addition, we docu- mented age, sex, body weight, height, and body mass index of all partic- ipants. Furthermore, participants were asked to give a self-estimation of their performance with and without the device.

Statistical analysis

Statistica Package Software (version 12.5; StatSoft Inc, Tulsa, OK) was used for statistical analysis. The results were presented as absolute values, percentages, median and interquartile range (IQR), or mean and standard deviation (SD). The Kolmogorov-Smirnov test was applied to check for normal distribution. As this was a randomized crossover trial, pairing was taken into account in the statistical analysis. All P values are 2-sided, and P b .05 was considered to be statistically

Fig. 2. Flowchart of design and recruitment of participants according to the CONSORT statement.

significant. Student t test was used for paired samples with normal dis- tribution, and Wilcoxon test was used for samples with nonparametric distribution.

Power calculation“>Power calculation

Based on pilot data, we assumed an ? risk of .05 and a ? risk of .2 for sample size calculation. The percentage of effective compressions in pilot data using the manual CPR and ARM varied and amounted to 44.3% vs 100% (standard BLS and ARM). We calculated that at least 31 participants would be required (paired, 2-sided). Participants were ran- domized with a 1:1 ratio.

Results

Seventy-eight paramedics (22 female; 28.2%) participated. The sex ratio of our trial was representative of Polish EMS staff. Seventy-five subjects (17 female; 29.8%) worked in EMS and 21 (5 female; 23.8%) in hospital emergency units. Mean age was 28.4 +- 5.9 years, mean work experience was 2.3 +- 1.3 years, mean height was 168 +- 19 cm, and mean weight was 79.5 +- 11.5 kg.

Using the ARM during resuscitation resulted in a higher percentage of effective compressions (100 [IQR, 99-100]) compared with manual CCs (43 [IQR, 39-46]; P b .001). The number of effective compressions

decreased over time with ARM by 0.05% per minute and with manual CCs by 0.86% per minute (P b .001).

CCs using ARM significantly more often reached the required depth of 5 cm compared with manual BLS (97% vs 63%, P b .001)). CC quality of the different scenarios is presented in Table 1.

There was significant difference in baseline median compression rate between groups (Table 1). Median CCs rates were 100 min^-1 when using ARM and 135 min^-1 when CC was performed manually. CCs were significantly faster in standard BLS than ARM (P b .001).

CCs using ARM compared with manual CCs were performed more correctly regarding depth (97% vs 63%; P b .001), correct pressure point (91% vs 100%; P = .023), and correct pressure release (100% vs

85%; P b .001).

Table 1

Chest compression parameters (observation period, 8 minutes; median [IQR])

CC parameters	Standard BLS	ARM	P value
Effective compressions (%)	43 (39-46)	100 (99-101)	b.001
Correct CC depth (%)	63 (55-73)	97 (95-99)	b.001
CC too deep (%)	16 (9-33)	2 (1-3)	b.001
CC too shallow (%)	21 (14-45)	1 (1-2)	b.001
Mean CC rate (min-1)	135 (124-140)	100 (99-101)	b.001
Mean CC depth (mm)	37 (30-39)	52 (51-54)	b.001
Correct pressure point (%)	91 (71-100)	100 (99-100)	.023
Correct pressure release (%)	85 (67-91)	100 (99-100)	b.001

The results with ARM were significantly better than with manual CCs (P b .05) for all analyzed time-related parameters (absolute hands-of time, hands-off time, ventilation time; Table 2). The median tidal volume was higher when CPR was performed using ARM. Gastric inflations were significantly higher with manual CCs (Table 3).

Discussion

We hereby showed for the first time that CC during CPR with the Lifeline ARM is feasible and provides more effective CCs compared with manual CCs. Moreover, the number of effective CCs decreased less over time with ARM, and CCs were more often performed correctly regarding depth, pressure point, and pressure release. Importantly, re- sults with ARM were significantly better than with manual CCs for all analyzed time-related parameters (Table 2).

CCs are the most important cornerstone of CPR. Mechanical CC de- vices have been developed to better deliver uninterrupted CCs of good quality [25]; latest guidelines support their use when sustained high- quality manual CCs are impractical or compromise safety [4]. Several automated CC devices have been tested for their use in CPR so far [25]. Three major studies including more than 11 000 patients on the use of automated mechanical CC devices raise no serious doubt about the safe- ty of automated mechanical CC devices [26-28]. Several meta-analyses and reviews did not reveal any profound risks or evidence of inferiority of automated mechanical CC devices. It has further been shown that a protocol using mechanical CC devices reduced interruptions in CCs and enabled defibrillation during ongoing compressions without ad- versely affecting other resuscitation process metrics [29]. This device has been developed to comply with the latest ERC guidelines [4].

Comparing automated CC with the ARM to manual CC, we found bet- ter results with the ARM (effective compressions, correct depth, CC rate, correct pressure point, correct pressure release). Regarding CC rate, compression rates between 100 and 120 per minute were associated with greatest survival to hospital discharge [6]. Regarding depth, recent studies found a strong association between survival outcomes and in- creased compression depth [30]. Pressure release was also significantly better with the ARM but is not associated with any clear benefit [31]. The LUCAS device improved CPR quality by reducing the No-flow time and by improving the quality of CC compared with manual CPR during preclinical resuscitation [32]; data on CC depth of CPR were not reported [23]. Contrariwise, in a large trial among patients with out-of-hospital cardiac arrest in whom CPR was performed, a strategy of continuous CCs with positive-pressure ventilation did not result in significantly higher rates of survival or favorable neurologic status compared with a strategy of CCs interrupted for ventilation [33]. This study does not eliminate a possible fatigue of the CC provider because all groups in- volved manual CCs, so the conclusion cannot be directly transferred to our trial. Also, as the authors themselves state, posttreatment factors that may have influenced the outcome were not attributed, some of them being critical for outcome [34]. There were also benefits of the ARM with regard to hands-off time and ventilation time while reducing gastric inflations. Studies with the LUCAS device found no significant difference between techniques in terms of hands-off time [35]. Ventila- tion is an issue not sufficiently assessed in all investigations on automat- ed CC. This might pose a strength of our study because we were able-by using a manikin-to report ventilation time and tidal volume, both

Table 2

Time-related parameters (observation period, 8 minutes; median [IQR])

Time-related parameters	Standard BLS	ARM	P value
Absolute hands-off time (s)a	182 (174-199)	54 (50-59)	b.001
Hands-off time (s)	235 (221-277)	115 (112-117)	b.001
Ventilation time (s)	48 (43-58)	72 (70-74)	b.001

^a Sum of all periods during which no hand was placed on the chest minus time used for ventilation.

Table 3

Ventilation parameters (observation period, 8 minutes; median [IQR])

Ventilation parameters Standard BLS ARM P value Tidal volume (L) 0.4 (0.32 +- 0.42) 0.52 (0.48-0.56) b.001

Ventilation rate (min) 3.8 (3.3-4.0) 6 (5-7) b.001

Minute volume (L) 1.56 (1.0 +- 1.6) 2.7 (2.3-2.8) b.001

Gastric inflations (%) 4 (3-8) 0 (0-1) b.001

being higher in the ARM group. However, one cannot conclude from these data that a higher tidal volume might necessarily lead to a better outcome in a real-life resuscitation scenario, but lack of proper oxygen- ation for sure does not. Also, there are reports of fatal outcome due to gastric overinflation [15-17]. Of note, each participant was well trained and skilled in bag-valve-mask ventilation with experience in more than 20 CPRs. Hence, the observed differences in tidal volume cannot be ex- plained by the different levels of experience with bag-valve-mask ven- tilation and may therefore be attributed to the device itself. The aforementioned study did not investigate a potential difference of oxy- genation or ventilation between the 2 treatment strategies [33]: our study shows that indeed ventilation time and tidal volume were higher with uninterrupted CCs, thus potentially providing better oxygenation but also higher intrathoracic pressure impairing coronary perfusion [36]. The use of standard simulation manikins instead of real patients creates some limitations. The SimMan manikin is generally acceptably realistic but has significant limitations compared with real humans [37]. It is probably easier to place the device properly on a standard- size manikin than on an overweight clothed person in cardiac arrest; the same is true for CCs. Furthermore, the manikin’s anatomy may favor a distinct CC device, as has been shown for supraglottic airway de- vices [38,39]. However, manikins allow for simulating the exact same situations for each participant and pose the only way to simulate stan- dardized CC to date. All participants in our study were experts in the field of emergency medicine, but mean work experience was 2.3 years, which is rather short. More experienced EMTs might be more ef- fective with manual CC, most likely because of their everyday practice. We did not measure time until proper setup of the ARM. This is of importance because interruptions of CC to apply automated CC devices can be significantly long, and users do not perceive pause time accurate- ly [40]. Also, overall better CCs in the long term can be counterbalanced by the initial longer period of hands-off time to place the device proper- ly. However, because our primary outcome was effective CCs, introduc- ing a setup period with one paramedic providing CCs while the other sets up the device would not provide a clean comparison but would in daily practice solve this problem. Another limitation is that the effects of this mechanical CC device on resuscitation-Associated injuries cannot be judged in manikins, although this poses an important issue in postresuscitation care [41]. Although there are observational studies that suggest that mechanical CCs could improve survival to hospital ad- mission, the cumulative randomized evidence does not support a rou-

tine strategy of mechanical CPR to improve outcome [42].

Conclusively, we showed that the Lifeline ARM CC device provides more effective CCs compared with manual CCs, more ventilation time and minute volume, and less hands-off time and that the number of ef- fective CCs decreased less over time. Mechanical CCs in our study adhere more closely to current guidelines than manual CCs. We propose to test the ARM in comparison with the LUCAS CC system and the ZOLL AutoPulse.

References

1. Atwood C, Eisenberg MS, Herlitz J, Rea TD. Incidence of EMS-treated out-of-hospital cardiac arrest in Europe. Resuscitation 2005;67(1):75-80.
2. Kleinman ME, Brennan EE, Goldberger ZD, Swor RA, Terry M, Bobrow BJ, et al. Part 5: adult basic life support and cardiopulmonary Resuscitation quality: 2015 American Heart Association guidelines update for cardiopulmonary resuscitation and emer- gency cardiovascular care. Circulation 2015;132(18 Suppl. 2):S414-35.
3. Link MS, Berkow LC, Kudenchuk PJ, Halperin HR, Hess EP, Moitra VK, et al. Part 7: adult advanced cardiovascular life support: 2015 American Heart Association guide- lines update for cardiopulmonary resuscitation and emergency cardiovascular care. Circulation 2015;132(18 Suppl. 2):S444-64.
4. Soar J, Nolan JP, Bottiger BW, Perkins GD, Lott C, Carli P, et al. European Resuscitation Council guidelines for resuscitation 2015: section 3. Adult advanced life support. Re- suscitation 2015;95:100-47.
5. Perkins GD, Handley AJ, Koster RW, Castren M, Smyth MA, Olasveengen T, et al. European Resuscitation Council guidelines for resuscitation 2015: section 2. Adult basic life support and Automated external defibrillation. Resuscitation 2015;95:81-99.
6. Idris AH, Guffey D, Pepe PE, Brown SP, Brooks SC, Callaway CW, et al. Chest compres- sion rates and survival following out-of-hospital cardiac arrest. Crit Care Med 2015; 43(4):840-8.
7. Idris AH, Guffey D, Aufderheide TP, Brown S, Morrison LJ, Nichols P, et al. Relation- ship between chest compression rates and outcomes from cardiac arrest. Circulation 2012;125(24):3004-12.
8. Kern KB, Hilwig RW, Berg RA, Sanders AB, Ewy GA. Importance of continuous chest compressions during cardiopulmonary resuscitation: improved outcome during a simulated single lay-rescuer scenario. Circulation 2002;105(5):645-9.
9. Heidenreich JW, Bonner A, Sanders AB. rescuer fatigue in the elderly: standard vs. Hands-only CPR. J Emerg Med 2012;42(1):88-92.
10. Heidenreich JW, Berg RA, Higdon TA, Ewy GA, Kern KB, Sanders AB. Rescuer fatigue: standard versus continuous chest-compression cardiopulmonary resuscitation. Acad Emerg Med 2006;13(10):1020-6.
11. Hightower D, Thomas SH, Stone CK, Dunn K, March JA. Decay in quality of closed- chest compressions over time. Ann Emerg Med 1995;26(3):300-3.
12. Ruiz de Gauna S, Gonzalez-Otero DM, Ruiz J, Russell JK. Feedback on the rate and depth of chest compressions during cardiopulmonary resuscitation using only accel- erometers. PLoS One 2016;11(3):e0150139.
13. Kurowski A, Szarpak L, Bogdanski L, Zasko P, Czyzewski L. Comparison of the effective- ness of cardiopulmonary resuscitation with standard manual chest compressions and the use of TrueCPR and PocketCPR Feedback devices. Kardiol Pol 2015;73(10):924-30.
14. Brooks SC, Anderson ML, Bruder E, Daya MR, Gaffney A, Otto CW, et al. Part 6: alter- native techniques and ancillary devices for cardiopulmonary resuscitation: 2015 American Heart Association guidelines update for cardiopulmonary resuscitation and emergency cardiovascular care. Circulation 2015;132(18 Suppl. 2):S436-43.
15. Sajith A, O’Donohue B, Roth RM, Khan RA. CT scan findings in oesophagogastric perfora- tion after out of hospital cardiopulmonary resuscitation. Emerg Med J 2008;25(2):115-6.
16. Camden JR, Carucci LR. liver injury diagnosed on computed tomography after use of an automated cardiopulmonary resuscitation device. Emerg Radiol 2011;18(5):429-31.
17. de Rooij PP, Wiendels DR, Snellen JP. Fatal complication secondary to mechanical chest compression device. Resuscitation 2009;80(10):1214-5.
18. Buschmann CT, Tsokos M. Frequent and rare complications of resuscitation at- tempts. Intensive Care Med 2009;35(3):397-404.
19. Koller AC, Salcido DD, Menegazzi JJ. Perishock pause intervals and rearrest after out- of-hospital cardiac arrest. J Emerg Med 2016;50(2):263-9.
20. Cheskes S, Schmicker RH, Christenson J, Salcido DD, Rea T, Powell J, et al. Perishock pause: an independent predictor of survival from out-of-hospital shockable cardiac arrest. Circulation 2011;124(1):58-66.
21. Couper K, Smyth M, Perkins GD. mechanical devices for chest compression: to use or not to use? Curr Opin Crit Care 2015;21(3):188-94.
22. Lewis RJ, Niemann JT. Manual vs device-assisted CPR: reconciling apparently contra- dictory results. JAMA 2006;295(22):2661-4.
23. Tranberg T, Lassen JF, Kaltoft AK, Hansen TM, Stengaard C, Knudsen L, et al. Quality of cardiopulmonary resuscitation in out-of-hospital cardiac arrest before and after in- troduction of a Mechanical chest compression device, LUCAS-2; a prospective, ob- servational study. Scand J Trauma Resusc Emerg Med 2015;23:37.
24. Truszewski Z, Szarpak L, Kurowski A, Evrin T, Madziala M, Czyzewski L. Mechanical chest compression with the LifeLine ARM device during simulated CPR. Am J Emerg Med 2016;34(5):917.
25. Rubertsson S. Update on mechanical cardiopulmonary resuscitation devices. Curr Opin Crit Care 2016.
26. Perkins GD, Lall R, Quinn T, Deakin CD, Cooke MW, Horton J, et al. Mechanical versus manual chest compression for out-of-hospital cardiac arrest (PARAMEDIC): a prag- matic, cluster randomised controlled trial. Lancet 2015;385(9972):947-55.
27. Rubertsson S, Lindgren E, Smekal D, Ostlund O, Silfverstolpe J, Lichtveld RA, et al. Me- chanical chest compressions and simultaneous defibrillation vs conventional cardio- pulmonary resuscitation in out-of-hospital cardiac arrest: the LINC randomized trial. JAMA 2014;311(1):53-61.
28. Wik L, Olsen JA, Persse D, Sterz F, Lozano Jr M, Brouwer MA, et al. Manual vs. inte- grated automatic load-distributing band CPR with equal survival after out of hospital cardiac arrest. The randomized CIRC trial. Resuscitation 2014;85(6):741-8.
29. Esibov A, Banville I, Chapman FW, Boomars R, Box M, Rubertsson S. Mechanical chest compressions improved aspects of CPR in the LINC trial. Resuscitation 2015; 91:116-21.
30. Stiell IG, Brown SP, Christenson J, Cheskes S, Nichol G, Powell J, et al. What is the role of chest compression depth during out-of-hospital cardiac arrest resuscitation? Crit Care Med 2012;40(4):1192-8.
31. Lafuente-Lafuente C, Melero-Bascones M. Active chest compression-decompression for cardiopulmonary resuscitation. Cochrane Database Syst Rev 2013;9, CD002751.
32. Putzer G, Braun P, Zimmermann A, Pedross F, Strapazzon G, Brugger H, et al. LUCAS compared to Manual cardiopulmonary resuscitation is more effective during heli- copter rescue-a prospective, randomized, cross-over manikin study. Am J Emerg Med 2013;31(2):384-9.
33. Nichol G, Leroux B, Wang H, Callaway CW, Sopko G, Weisfeldt M, et al. Trial of con- tinuous or interrupted chest compressions during CPR. N Engl J Med 2015;373(23): 2203-14.
34. Girotra S, Chan PS, Bradley SM. post-resuscitation care following out-of-hospital and in-hospital cardiac arrest. Heart 2015;101(24):1943-9.
35. Maurin O, Frattini B, Jost D, Galinou N, Allanati L, Dang Minh P, et al. Hands-off time during automated chest compression device application in out-of-hospital cardiac arrest: a case series report. Prehosp Emerg Care 2016;1-6.
36. Yannopoulos D, Aufderheide TP, Gabrielli A, Beiser DG, McKnite SH, Pirrallo RG, et al. Clinical and hemodynamic comparison of 15:2 and 30:2 compression-to-ventilation ratios for cardiopulmonary resuscitation. Crit Care Med 2006;34(5):1444-9.
37. Hesselfeldt R, Kristensen MS, Rasmussen LS. Evaluation of the airway of the SimMan full-scale patient simulator. Acta Anaesthesiol Scand 2005;49(9):1339-45.
38. Cook TM, Green C, McGrath J, Srivastava R. Evaluation of four airway training man- ikins as patient simulators for the insertion of single use laryngeal mask airways. An- aesthesia 2007;62(7):713-8.
39. Silsby J, Jordan G, Bayley G, Cook TM. Evaluation of four airway training manikins as simulators for inserting the LMA classic*. Anaesthesia 2006;61(6):576-9.
40. Yost D, Phillips RH, Gonzales L, Lick CJ, Satterlee P, Levy M, et al. Assessment of CPR interruptions from transthoracic impedance during use of the LUCAS mechanical chest compression system. Resuscitation 2012;83(8):961-5.
41. Koga Y, Fujita M, Yagi T, Nakahara T, Miyauchi T, Kaneda K, et al. Effects of mechan- ical chest compression device with a load-distributing band on post-resuscitation in- juries identified by post-mortem computed tomography. Resuscitation 2015;96: 226-31.
42. Bonnes JL, Brouwer MA, Navarese EP, Verhaert DV, Verheugt FW, Smeets JL, 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(3): 349-60 [e343].