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Poor chest compression quality with mechanical compressions in simulated cardiopulmonary resuscitation: A randomized, cross-over manikin study
Resuscitation 82 (2011) 1332–1337
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Simulation and education
Poor chest compression quality with mechanical compressions in simulated cardiopulmonary resuscitation: A randomized, cross-over manikin study夽 Hans Blomberg a,b,∗ , Rolf Gedeborg a,c , Lars Berglund c , Rolf Karlsten a , Jakob Johansson a,b a b c
Department of Surgical Sciences - Anesthesiology & Intensive Care, Uppsala University, SE-751 85 Uppsala, Sweden Centre of Emergency Medicine, Uppsala University Hospital, SE-751 85 Uppsala, Sweden Uppsala Clinical Research Center, Uppsala University, SE-751 85 Uppsala, Sweden
a r t i c l e
i n f o
Article history: Received 14 February 2011 Received in revised form 16 May 2011 Accepted 1 June 2011
Keywords: Cardiopulmonary resuscitation (CPR) Defibrillation Cardiac arrest Chest compression Out-of-hospital CPR Cardiac-assist device
a b s t r a c t Introduction: Mechanical chest compression devices are being implemented as an aid in cardiopulmonary resuscitation (CPR), despite lack of evidence of improved outcome. This manikin study evaluates the CPRperformance of ambulance crews, who had a mechanical chest compression device implemented in their routine clinical practice 8 months previously. The objectives were to evaluate time to first defibrillation, no-flow time, and estimate the quality of compressions. Methods: The performance of 21 ambulance crews (ambulance nurse and emergency medical technician) with the authorization to perform advanced life support was studied in an experimental, randomized cross-over study in a manikin setup. Each crew performed two identical CPR scenarios, with and without the aid of the mechanical compression device LUCAS. A computerized manikin was used for data sampling. Results: There were no substantial differences in time to first defibrillation or no-flow time until first defibrillation. However, the fraction of adequate compressions in relation to total compressions was remarkably low in LUCAS-CPR (58%) compared to manual CPR (88%) (95% confidence interval for the difference: 13–50%). Only 12 out of the 21 ambulance crews (57%) applied the mandatory stabilization strap on the LUCAS device. Conclusions: The use of a mechanical compression aid was not associated with substantial differences in time to first defibrillation or no-flow time in the early phase of CPR. However, constant but poor chest compressions due to failure in recognizing and correcting a malposition of the device may counteract a potential benefit of mechanical chest compressions. © 2011 Elsevier Ireland Ltd. All rights reserved.
1. Introduction It is estimated that approximately 275,000 cardiac arrests are treated by emergency medical services annually in Europe, with 10.7% survival to hospital discharge.1 A similar survival proportion of 8.4% is reported from the United States.2 Recent guidelines in cardiopulmonary resuscitation (CPR) state the importance of chest compression quality, including reducing the time without compressions (no-flow time) during CPR.3,4 Despite this, both in-hospital and out of hospital studies have indi-
夽 A Spanish translated version of the abstract of this article appears as Appendix in the final online version at doi:10.1016/j.resuscitation.2011.06.002. ∗ Corresponding author at: Department of Surgical Sciences - Anesthesiology & Intensive Care, Uppsala University, SE-751 85 Uppsala, Sweden. Tel.: +46 18 6110000; fax: +46 18 559357. E-mail addresses: [email protected] (H. Blomberg), [email protected] (R. Gedeborg), [email protected] (L. Berglund), [email protected] (R. Karlsten), [email protected] (J. Johansson). 0300-9572/$ – see front matter © 2011 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.resuscitation.2011.06.002
cated suboptimal chest compressions and undesirably long no-flow times.5–7 The importance of correct performance of compressions has been demonstrated in both animal studies and human studies.8–11 Both increased compression depth and lowered noflow time are associated with increased likelihood of defibrillation success in clinical studies.12,13 Several mechanical compression devices are now available on the market but it is unknown if they increase survival rate.14–19 Studies of new devices, drugs and protocols in CPR are often performed in well-defined laboratory settings during predefined periods of time, and with a selected and dedicated staff given specific training. This may explain why subsequent evaluation of actual performance and outcome after implementation in routine clinical practice can yield conflicting results.20 There are few studies on the quality of performance when mechanical compression devices are used in routine clinical practice and how this influences other interventions (e.g. ventilation and time to defibrillation) during CPR.21 The objective of the present manikin study was to evaluate the CPR performance of ambulance crews, who had a mechanical chest compression device implemented in their routine clinical practice.
H. Blomberg et al. / Resuscitation 82 (2011) 1332–1337
Manual compressions
6
Mechanical compressions
Compression depth (cm)
LUCAS out of position
5
1333
Correction of LUCAS position
Defibrillation
4 3.8
Defibrillation
Defibrillation
3 2 1 0
0
150
300
Seconds
450
600
Fig. 1. A sample registration of one ambulance crew performing LUCAS-CPR. In this case mechanical compressions are started after 170 s of CPR. Initially the compression depths are adequate (>3.8 cm), but LUCAS is sliding out of position resulting in shallow compressions. After a delayed correction, adequate compression depths are reestablished.
Two specific hypotheses were tested in this comparison of CPR with a mechanical device to CPR with manual compressions only: (i) that the use of the mechanical device delays first defibrillation and (ii) that the use of the mechanical device increases no-flow time until the first defibrillation. To accomplish this we conducted a randomized, crossover study in ambulance crews that have incorporated a mechanical compression device in their standard treatment protocol for CPR. Full-scale CPR scenarios in a manikin setup were used in order resemble CPR in clinical practice. 2. Methods 2.1. Study population The following criteria were used to select a Swedish ambulance organization suitable for the study: (a) it should not be connected to the investigators’ own organization, (b) a mechanical compression device should be a part of the standard treatment of cardiac arrest and incorporated in regular practice, (c) the organization should use the mechanical compression device as a pure replacement for manual compressions, and (d) the ambulance organization should not be involved in any studies concerning CPR. Based on these criteria, an ambulance organization with 160 employees working at six different ambulance stations was approached. The staff consisted of 72% nurses and 28% emergency medical technician equivalents (EMT equivalents; a nursing assistant with special ambulance training comparable to a paramedic education). The mechanical compression device LUCAS (Lund University Cardiopulmonary Assist System, Jolife AB, Lund, Sweden) had been utilized for 8 months. The organization had two different protocols for CPR; one for LUCAS-CPR used in ambulances equipped with the mechanical device and one for manual CPR in the other ambulances. As a part of their standard CPR-protocol with LUCAS, manual compressions were performed until the LUCAS device was applied. As mandatory in Sweden each ambulance was staffed with at least one nurse, authorized to perform advanced life support according to the 2005 ERC-guidelines with the recommended compression rate of 100 min−1 , depth of 4–5 cm and minimizing the no-flow time.22 The staff received centralized training and certification in CPR two times every 3 years, complemented by locally
arranged CPR training two times a year. With the introduction of LUCAS there was a 4-h hands-on training program in CPR with LUCAS with an instructor from the manufacturer, complemented by at least one local training session. The training program focuses on application of the device, correct positioning and the use of a stabilization strap. By randomly drawing employee identity numbers, unique for each of the 160 employees, 54 nurses and EMT equivalents forming 27 crews were selected. In case of two EMTs one was by randomization replaced, generating at least one nurse in each crew. Seven crew members could not attend as required. One of them was replaced without randomization, giving a total of 24 crews entering the study. No additional training in CPR was provided before the study. The participants were not informed about the hypotheses of the study. The need for ethical approval was waived by the Regional Ethical Review Board. 2.2. Study design Each crew served as their own control performing two 10min full CPR scenarios according to their ordinary CPR-protocol; one scenario with the aid of LUCAS (LUCAS-CPR) and one identical scenario but with only manual compressions (manual CPR). The crews were given written and verbal information about the study setup. A random selection with sealed envelopes determined which scenario to perform first. The following scenario was presented: “Sudden unconsciousness of a 45-year-old male. On your arrival more than five minutes have elapsed. You will find neither pulse nor respiration and no bystander CPR has been performed. No signs of trauma.” After the first scenario the crews were given 30 min rest, and then an identical CPR scenario was presented but a crossover to the other type of chest compression protocol was done. A computerized manikin (Resusci Anne Simulator, Laerdal Medical, Stavanger, Norway) was used with software developed by Jolife AB, Lund, Sweden. The manikin was modified by Jolife AB to accept venous cannulation and advanced airway management, and to measure compression depths more accurately (±0.1 cm) within a radius of 5 cm. Chest compression frequency and depth were automatically recorded. Fig. 1 illustrates one LUCAS-CPR registration in a condensed format.
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H. Blomberg et al. / Resuscitation 82 (2011) 1332–1337 Table 1 Demographics of the 42 individual crew members.
Key interventions, such as pulse check, first chest compression, defibrillation, drug administrations, and when applicable: first mechanical compression, application of stabilization strap, and correction of LUCAS position were manually tagged in the computerized log. Video recording was used for retrospective verification. The ECG simulator was set on refractory ventricular fibrillation throughout the experiment.
Age, years 39 (35–46) Gender, n (%) Male 30 (71) 12 (29) Female Basic medical education, n (%) 11 (26) Emergency medical technician equivalent 31 (74) Registered nurse 137 (71–230) Experience in prehospital care, months Number of performed training sessions in CPR 11 (7–20) With manual chest compressions 3 (2–4) With the LUCAS device Number of weeks since last training session in CPR 3 (2–24) With manual compressions 3 (1–9) With the LUCAS device Number of performed CPRs in clinical practice 25 (16–50) With manual chest compressions 2 (1–3) With the LUCAS device Number of weeks since last performance of CPR in clinical practice 20 (10–32) With manual chest compressions 12 (4–52) With the LUCAS device
2.3. Definitions According to an international consensus working group, compression depths ≥3.8 cm were considered as adequate.23 No-flow time was defined as intervals of more than 1.5 s without compressions. No-flow fraction was defined as no-flow time during a specified interval divided by the total time of this interval. 2.4. Description of the mechanical compression device, LUCAS
Continuous variables are given as median with interquartile range (IQR).
LUCAS is a battery driven rechargeable chest compression device. A piston with a suction cup made of silicon rubber delivers compressions with depths of 4–5 cm. The frequency of the compressions is 100 ± 5 min−1 . In between every 30th compression there is a 3-s pause allowing ventilation. The piston is adjusted vertically so that the suction cup is just in contact with the chest wall and in the horizontal plane the lower edge of the suction cup should be immediately above the distal end of the sternum. To avoid sliding, a stabilization strap is wrapped around the shoulders.
calculated using a bootstrap procedure with 1,000 replications and the percentile method. The statistical packages SAS version 9 (SAS Institute Inc., Cary, NC, USA), Stata/SE 11.0 (StataCorp, College Station, TX), and R version 2.7.0 (R Foundation for Statistical Computing, Vienna, Austria) were used for statistical analyses. Results are presented either as mean with 95% confidence interval or median with Inter Quartile Range (IQR) as appropriate. Since the hypothesis included two primary endpoints a p-value of less than 0.025 was considered statistically significant (Bonferroni correction).
2.5. Statistical methods A sample size calculation was performed under the assumption that a difference of 30 s in time to first defibrillation or a 5% difference in no-flow time until first defibrillation would be clinically important.24–27 For both of these primary endpoints, correlation between the two repeated measurements of the same ambulance crew was assumed to be 0.5. It was then estimated that a total of 48 scenarios (24 ambulance crews performing two scenarios) would be sufficient to detect differences of that magnitude with at least 80% power. The Shapiro Wilks W-statistic indicated that the primary endpoints were non-normally distributed even after logarithmic transformation (W-statistic <0.95). Treatment groups were therefore compared using the Wilcoxon matched pairs signed rank test. No carry over effects interfered with this test.28 Confidence intervals for the mean differences between the treatments were
3. Results Three out of the 24 ambulance crews were excluded; one crew because of technical problems such that data sampling was not possible and two crews failed to appear due to illness. The individual profiles of the remaining 42 ambulance crew members are presented in Table 1. There was no substantial difference in time to first defibrillation (manual CPR 178 s, versus LUCAS-CPR 182 s, p = 0.56), or the noflow time prior to first defibrillation (73 s versus 79 s, p = 0.04), see Table 2. There was no difference in no-flow fraction, either prior to first defibrillation or for the whole scenario (Table 2). There were differences in the compression quality when using LUCAS compared to manual compressions (Table 3). For the whole
Table 2 Time to 1st defibrillation, no-flow, frequencies and time to key interventions.
Time to 1st defibrillation (s) No-flow time until 1st defibrillation (s) No-flow time for the whole scenario (s) No-flow fraction (%) Prior 1st defibrillation For the whole scenario Compression frequency (min−1 ) Prior 1st defibrillation For the whole scenario Time to performed (s) First chest compression First ventilation mouth to mask First ventilation on laryngeal mask Intravenous cannulation First administration of adrenaline
CPR with mechanical compression aid (LUCAS-CPR)
CPR without mechanical compression aid (manual CPR)
Mean difference
182 79 181
178 73 200
4 6 −20
44 30
41 33
3 −3
118 104
128 129
−10 −25
−15 to 5 −29 to −20
15 66 231 206 503
13 57 293 106 494
1 9 −62 100 9
−1 to 3 −17 to 30 −114 to −11 79 to 123 −8 to 29
95% confidence interval
p-Value
−12 to 21 0 to 12 −36 to 1
0.56 0.04
0 to 6 −6 to 0
Presented as the mean difference between LUCAS-CPR and manual CPR, 95% confidence interval for the difference, and p-value for the primary endpoints.
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Table 3 Adequacy of compressions.
Compressions prior to 1st defibrillation Total number of compressions, n Fraction of adequatea compressions (%) Number of manual compressions Fraction of adequatea manual compressions (%) Number of mechanical compressions Fractions of adequatea mechanical compressions (%) Compressions during the whole scenario Total number of compressions Fraction of adequatea compressions (%) Number of manual compressions Fraction of adequatea manual compressions (%) Number of mechanical compressions Fractions of adequatea mechanical compressions (%)
CPR with mechanical compression aid (LUCAS-CPR)
CPR without mechanical compression aid (manual CPR)
Mean difference
95% confidence interval
199 71% 114b 89%b 85 46%
221 94% 221 94%
−21 −23%
−48 to 1 −37% to −8%
732 58% 116b 88%b 617 52%
856 88% 856 88%
−124 −30%
−5%
0%
−12% to 3%
−155 to −91 −50% to −13% −9% to 7%
Presented as the mean difference between LUCAS-CPR and manual CPR and 95% confidence interval for the difference. a Adequate compression defined as compression depth ≥3.8 cm. b The manual compressions in LUCAS-CPR is done before the application of the mechanical device.
scenario, the number of adequate compressions in manual CPR was 78% higher in relation to LUCAS-CPR (750 versus 422). Analyzing adequate compressions as a fraction of the total number of chest compressions in order to minimize the influence of the higher compression rate during manual CPR gave similar results. Manual CPR was associated with a higher fraction of adequate compressions than LUCAS-CPR (Fig. 2). The median compression depth for mechanical compressions was 3.8 (IQR 3.7–4.6) and for manual compressions 4.7 (IQR 4.5–5.0). In LUCAS-CPR, median time to first mechanical compression was 100 s (IQR 91–132). Correction of a malposition of LUCAS was done by five ambulance crews (24%), as verified by video review, with a median time from the first inadequate compression to correction of 241 s (IQR 197–371). In one case the correction was insufficient, i.e. not leading to adequate compressions after the correction. The video recording also documented that in LUCAS-CPR only 12 out of the 21 ambulance crews (57%) applied the stabilization strap on the LUCAS device. The median time from first mechanical compression to application of the strap was 249 s (IQR 135–321). 3.1. Performance of mechanical compressions in relation to educational level and professional experience The fraction of adequate mechanical compressions did not differ depending on the level of education of the crews (51% with two nurses versus 50% with one nurse and one EMT, 95% CI for
difference: −37% to 39%). The results did not indicate substantial correlations between the fraction of adequate mechanical compressions and any of the following factors: number of performed training sessions using LUCAS-CPR (correlation coefficient −0.05, 95% CI −0.47 to 0.39), number of performed LUCAS-CPR in clinical practice (correlation coefficient 0.02, 95% CI −0.41 to 0.45), time since last training session using LUCAS-CPR (correlation coefficient −0.16, 95% CI −0.55 to 0.30) or time since last performed LUCASCPR in clinical practice (correlation coefficient 0.17, 95% CI −0.29 to 0.53).
4. Discussion Our results indicate that the incorporation of a mechanical compression device in the CPR algorithm is possible without prolonging time to first defibrillation or substantially increasing no-flow time in the early phase of CPR. There was, however, a remarkably poor quality of compressions with the use of the mechanical device. This study was designed as a cross-over trial in order to reduce the influence of variation in performance between the ambulance crews. As indicated by the confidence intervals, the study had sufficient power to detect clinically meaningful differences in the primary endpoints of the study. The cross-over design in combination with a representative study population using an implemented new device contributes to the strength of the study.
Fig. 2. Panel A shows fraction of adequate compressions until 1st defibrillation. Panel B shows fraction of adequate compressions during the whole scenario of 10 min. Each line connects one crew’s results in LUCAS-CPR and manual CPR. Box-and-whisker plots for LUCAS-CPR and manual CPR, respectively. Boxes representing IQR, () median, whiskers representing max and min value (values more than three interquartile distances away from the median are considered outliers and are marked with dots).
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The strikingly poor quality of compressions with the mechanical device has several possible explanations. Incorrect application of LUCAS in the vertical plane, with a space between the piston and the chest wall, will generate too shallow compressions. Inappropriate horizontal position of LUCAS relative to the sternum, which could be due to either incorrect initial application or by sliding of the device during ongoing compressions, will generate misplaced and inadequate compressions. For unknown reasons, almost half of the ambulance crews neglected to apply the stabilization strap to the LUCAS device, and when applied, it was done with a substantial time delay. The sliding of LUCAS is a known phenomenon in clinical practice and therefore the usage of the stabilization strap is emphasized in the training program for the device.14 Sliding of the LUCAS device in clinical practice may be less common than in the manikin setting since the manikin is lighter than a human being and has a surface different from skin. This can, however, not explain failure to apply the stabilization strap or failure to observe and correct the position when sliding of the device occurred. Although malposition and/or sliding of the mechanical device were clearly verified by video review, objective measurements would certainly have been desirable. This would, however, have interfered with the continuation of the crews’ performance. The manikin setting may limit generalizability to clinical CPR. Even though our manikin had been modified to increase tolerance to malpositioned compressions, measurements of compression depth may be biased. ERC-guidelines clearly state the importance of correct positioning and adequate depths of compressions but the consequences of compressions classified as “not adequate” in the manikin setting are unknown for patient outcome in the clinical situation. Although animal studies indicate superior compression quality from mechanical compression devices,8,29 our study highlights the importance of quality control of performance after clinical implementation. An interesting observation was that airway management seemed to be prioritized when LUCAS is used, while intravenous access seemed to be prioritized when performing manual compressions. There was no correlation between time since last LUCAS-CPRtraining and quality of mechanical compressions. Little is known about skill retention over time in CPR training, but earlier studies suggest an interval of no more than 3–6 months between refresher courses.30 Thus, it is unlikely that the average of 3 weeks since last practice in this study population could explain the poor performance when using the mechanical compression device. A potential limitation of this study is that the artificial simulator setting may not reflect the performance of CPR in the clinical setting. The general conditions for CPR were unnaturally optimal in the study setting. The simulation setting might influence the incentive of the ambulance crew to perform their best. However, the quality of manual compressions and the performance of key interventions were comparable to previous studies in clinical settings indicating adequate overall performance from the studied crews.5,31 This study was performed on one single ambulance organization and the question of generalizability of the results must therefore be addressed. The criteria used for selecting the study population and the random selection of individuals was intended to select medical staff as representative as possible of an average Swedish ambulance organization. The fact that adherence to CPR guidelines in the study in terms of key interventions and quality of manual compressions were similar to results from other settings indicates that education and/or skill in CPR are representative of other ambulance organizations as well.5,31 Nevertheless, the quality of educational programs and instructor competence is an important aspect.32,33 Results from a multicentre study using another mechanical compression device (Autopulse) revealed a substantial variability in CPR performance with the mechanical device, despite a standardized
educational program.34 These results corroborate those of the present study. Mechanical devices for cardiac compressions are being implemented in routine clinical practice in spite of limited evidence to support their use from clinical outcome studies.18,19 Intuitively, these devices have obvious advantages. They enable the crew to be seated with safety belt applied while performing CPR during transport (as opposed to performance of manual compressions) and increase their ability to perform other important interventions due to alleviated workload.14 The devices also provide consistent compression rate and allow defibrillation during ongoing chest compressions. Some studies suggest improved CPR in special settings, such as catheter lab and during flights.35–37 However, our study indicates that there are still questions concerning the quality of chest compressions after widespread implementation of the device in clinical practice. Auditory real-time feedback utilized in automated external defibrillators could possibly be applied to mechanical compression devices as well.38 Previous clinical studies have failed to evaluate the adequacy of compression depth generated by the mechanical device.14,16,39 The device certainly delivers compressions with a constant depth. However, due to incorrect initial placement or sliding, it doesn’t necessarily generate adequate compression depth. If the poor compression quality found in this study reflects the performance in the clinical setting, this might partly explain failure to improve outcome in clinical trials. This study supports that study protocols should be optimized during simulations before launching large multicentre trials and that the quality of both manual and mechanical compressions should be evaluated in clinical studies.34 Furthermore, there is a need for clinical studies with focus on application and the feasibility of mechanical devices. The study was performed according to the 2005 AHA-guidelines. In the recently published 2010 AHA-guidelines the importance of adequate compression depth is further emphasized. The recommended depth of compression has increased from 1.5–2 in. to at least 2 in.40 These changes could be a potential limitation of the study but we have no reason to believe that the results would be substantially different if the study would have been performed after implementation of the 2010 AHA-guidelines. Our results support the 2010 AHA-guidelines which states that there is no evidence to recommend mechanical chest compression devices for routine clinical use41 but our results also imply that it is of utmost importance to ensure appropriate use of the device before evaluating the potential benefit in clinical trials. 5. Conclusion The study could not show that the use of the mechanical compression aid caused clinically meaningful differences in time to first defibrillation or no-flow time in the early phase of CPR. However, constant but poor chest compressions due to failure in recognizing and correcting a malposition of the device may erase a potential benefit of mechanical chest compressions. Further work is needed on how to assure the correct usage of mechanical chest compression devices before clinical evaluation and potential implementation in clinical practice. Conflict of interest statement Jolife AB provided the manikin and related technical support but was not involved in the design of the study, statistical analysis, interpretation of the results or the writing of the manuscript. Rolf Karlsten has once received a personal consultant fee from Jolife AB. All other authors declare that they have no financial or other conflicts of interest.
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Acknowledgements We gratefully acknowledge Bo Martinsson and Ulrika Eriksson, Jolife AB, for providing the manikin and related technical support. Dr. Stephen Butler is also gratefully acknowledged for language revision and Per Blomqvist for technical assistance. Source of funding for the study, for all authors, and for manuscript preparation: Uppsala University, Department of Surgical Sciences - Anaesthesiology & Intensive care. References 1. Atwood C, Eisenberg MS, Herlitz J, Rea TD. Incidence of EMS-treated out-ofhospital cardiac arrest in Europe. Resuscitation 2005;67:75–80. 2. Rea TD, Eisenberg MS, Sinibaldi G, White RD. Incidence of EMS-treated out-ofhospital cardiac arrest in the United States. Resuscitation 2004;63:17–24. 3. Nolan J. European resuscitation council guidelines for resuscitation 2005. Section 1. Introduction. Resuscitation 2005;67(Suppl. 1):S3–6. 4. Travers AH, Rea TD, Bobrow BJ, et al. Part 4: CPR overview: 2010 american heart association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care. Circulation 2010;122:S676–84. 5. Perkins GD, Boyle W, Bridgestock H, et al. Quality of CPR during advanced resuscitation training. Resuscitation 2008;77:69–74. 6. Abella BS, Alvarado JP, Myklebust H, et al. Quality of cardiopulmonary resuscitation during in-hospital cardiac arrest. J Am Med Assoc 2005;293:305–10. 7. Wik L, Kramer-Johansen J, Myklebust H, et al. Quality of cardiopulmonary resuscitation during out-of-hospital cardiac arrest. J Am Med Assoc 2005;293:299–304. 8. Steen S, Liao Q, Pierre L, Paskevicius A, Sjoberg T. Evaluation of LUCAS, a new device for automatic mechanical compression and active decompression resuscitation. Resuscitation 2002;55:285–99. 9. Halperin HR, Guerci AD, Chandra N, et al. Vest inflation without simultaneous ventilation during cardiac arrest in dogs: improved survival from prolonged cardiopulmonary resuscitation. Circulation 1986;74:1407–15. 10. Cobb LA, Fahrenbruch CE, Walsh TR, et al. Influence of cardiopulmonary resuscitation prior to defibrillation in patients with out-of-hospital ventricular fibrillation. J Am Med Assoc 1999;281:1182–8. 11. Steen PA, Kramer-Johansen J. Improving cardiopulmonary resuscitation quality to ensure survival. Curr Opin Crit Care 2008;14:299–304. 12. Edelson DP, Abella BS, Kramer-Johansen J, et al. Effects of compression depth and pre-shock pauses predict defibrillation failure during cardiac arrest. Resuscitation 2006;71:137–45. 13. Christenson J, Andrusiek D, Everson-Stewart S, et al. Chest compression fraction determines survival in patients with out-of-hospital ventricular fibrillation. Circulation 2009;120:1241–7. 14. Axelsson C, Nestin J, Svensson L, Axelsson AB, Herlitz J. Clinical consequences of the introduction of mechanical chest compression in the ems system for treatment of out-of-hospital cardiac arrest – a pilot study. Resuscitation 2006;71:47–55. 15. Wigginton JG, Isaacs SM, Kay JJ. Mechanical devices for cardiopulmonary resuscitation. Curr Opin Crit Care 2007;13:273–9. 16. Hallstrom A, Rea TD, Sayre MR, et al. Manual chest compression vs use of an automated chest compression device during resuscitation following out-of-hospital cardiac arrest: a randomized trial. J Am Med Assoc 2006;295:2620–8. 17. Ong ME, Ornato JP, Edwards DP, et al. Use of an automated, load-distributing band chest compression device for out-of-hospital cardiac arrest resuscitation. J Am Med Assoc 2006;295:2629–37. 18. Jacobs I. Mechanical chest compression devices – will we ever get the evidence? Resuscitation 2009;80:1093–4. 19. Perkins GD, Brace S, Gates S. Mechanical chest-compression devices: current and future roles. Curr Opin Crit Care 2010;16:203–10.
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20. Johansson J, Hammerby R, Oldgren J, Rubertsson S, Gedeborg R. Adrenaline administration during cardiopulmonary resuscitation: poor adherence to clinical guidelines. Acta Anaesthesiol Scand 2004;48:909–13. 21. Wang HC, Chiang WC, Chen SY, et al. Video-recording and time-motion analyses of manual versus mechanical cardiopulmonary resuscitation during ambulance transport. Resuscitation 2007;74:453–60. 22. Handley AJ, Koster R, Monsieurs K, Perkins GD, Davies S, Bossaert L. European resuscitation council guidelines for resuscitation 2005. Section 2. Adult basic life support and use of automated external defibrillators. Resuscitation 2005;67(Suppl. 1):S7–23. 23. Kramer-Johansen J, Edelson DP, Losert H, Kohler K, Abella BS. Uniform reporting of measured quality of cardiopulmonary resuscitation (CPR). Resuscitation 2007;74:406–17. 24. Jantti H, Kuisma M, Uusaro A. The effects of changes to the erc resuscitation guidelines on no flow time and cardiopulmonary resuscitation quality: a randomised controlled study on manikins. Resuscitation 2007;75:338–44. 25. Pytte M, Pedersen TE, Ottem J, Rokvam AS, Sunde K. Comparison of hands-off time during CPR with manual and semi-automatic defibrillation in a manikin model. Resuscitation 2007;73:131–6. 26. Roessler B, Fleischhackl R, Losert H, et al. Reduced hands-off-time and time to first shock in CPR according to the ERC guidelines 2005. Resuscitation 2009;80:104–8. 27. Maisch S, Issleib M, Kuhls B, et al. A comparison between over-the-head and standard cardiopulmonary resuscitation performed by two rescuers: a simulation study. J Emerg Med 2010;39:369–76. 28. Senn S.Cross-over trials in clinical research. 2nd ed. Chichester: Wiley; 2002. 29. Halperin HR, Paradis N, Ornato JP, et al. Cardiopulmonary resuscitation with a novel chest compression device in a porcine model of cardiac arrest: improved hemodynamics and mechanisms. J Am Coll Cardiol 2004;44:2214–20. 30. Hamilton R. Nurses’ knowledge and skill retention following cardiopulmonary resuscitation training: a review of the literature. J Adv Nurs 2005;51:288–97. 31. Ong ME, Annathurai A, Shahidah A, et al. Cardiopulmonary resuscitation interruptions with use of a load-distributing band device during emergency department cardiac arrest. Ann Emerg Med 2010;56:233–41. 32. Kaye W, Rallis SF, Mancini ME, et al. The problem of poor retention of cardiopulmonary resuscitation skills may lie with the instructor, not the learner or the curriculum. Resuscitation 1991;21:67–87. 33. Parnell MM, Larsen PD. Poor quality teaching in lay person cpr courses. Resuscitation 2007;73:271–8. 34. Tomte O, Sunde K, Lorem T, et al. Advanced life support performance with manual and mechanical chest compressions in a randomized, multicentre manikin study. Resuscitation 2009;80:1152–7. 35. Larsen AI, Hjornevik AS, Ellingsen CL, Nilsen DW. Cardiac arrest with continuous mechanical chest compression during percutaneous coronary intervention. A report on the use of the LUCAS device. Resuscitation 2007;75:454–9. 36. Agostoni P, Cornelis K, Vermeersch P. Successful percutaneous treatment of an intraprocedural left main stent thrombosis with the support of an automatic mechanical chest compression device. Int J Cardiol 2008;124:e19–21. 37. Fischer H, Neuhold S, Hochbrugger E, et al. Quality of resuscitation: flight attendants in an airplane simulator use a new mechanical resuscitation device – a randomized simulation study. Resuscitation 2011;82:459–63. 38. Handley AJ, Handley SA. Improving cpr performance using an audible feedback system suitable for incorporation into an automated external defibrillator. Resuscitation 2003;57:57–62. 39. Krep H, Mamier M, Breil M, Heister U, Fischer M, Hoeft A. Out-of-hospital cardiopulmonary resuscitation with the autopulse system: a prospective observational study with a new load-distributing band chest compression device. Resuscitation 2007;73:86–95. 40. Field JM, Hazinski MF, Sayre MR, et al. Part 1: Executive summary: 2010 american heart association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care. Circulation 2010;122:S640–56. 41. Cave DM, Gazmuri RJ, Otto CW, et al. Part 7: CPR techniques and devices: 2010 american heart association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care. Circulation 2010;122:S720–8.
Contents lists available at ScienceDirect
Resuscitation journal homepage: www.elsevier.com/locate/resuscitation
Simulation and education
Poor chest compression quality with mechanical compressions in simulated cardiopulmonary resuscitation: A randomized, cross-over manikin study夽 Hans Blomberg a,b,∗ , Rolf Gedeborg a,c , Lars Berglund c , Rolf Karlsten a , Jakob Johansson a,b a b c
Department of Surgical Sciences - Anesthesiology & Intensive Care, Uppsala University, SE-751 85 Uppsala, Sweden Centre of Emergency Medicine, Uppsala University Hospital, SE-751 85 Uppsala, Sweden Uppsala Clinical Research Center, Uppsala University, SE-751 85 Uppsala, Sweden
a r t i c l e
i n f o
Article history: Received 14 February 2011 Received in revised form 16 May 2011 Accepted 1 June 2011
Keywords: Cardiopulmonary resuscitation (CPR) Defibrillation Cardiac arrest Chest compression Out-of-hospital CPR Cardiac-assist device
a b s t r a c t Introduction: Mechanical chest compression devices are being implemented as an aid in cardiopulmonary resuscitation (CPR), despite lack of evidence of improved outcome. This manikin study evaluates the CPRperformance of ambulance crews, who had a mechanical chest compression device implemented in their routine clinical practice 8 months previously. The objectives were to evaluate time to first defibrillation, no-flow time, and estimate the quality of compressions. Methods: The performance of 21 ambulance crews (ambulance nurse and emergency medical technician) with the authorization to perform advanced life support was studied in an experimental, randomized cross-over study in a manikin setup. Each crew performed two identical CPR scenarios, with and without the aid of the mechanical compression device LUCAS. A computerized manikin was used for data sampling. Results: There were no substantial differences in time to first defibrillation or no-flow time until first defibrillation. However, the fraction of adequate compressions in relation to total compressions was remarkably low in LUCAS-CPR (58%) compared to manual CPR (88%) (95% confidence interval for the difference: 13–50%). Only 12 out of the 21 ambulance crews (57%) applied the mandatory stabilization strap on the LUCAS device. Conclusions: The use of a mechanical compression aid was not associated with substantial differences in time to first defibrillation or no-flow time in the early phase of CPR. However, constant but poor chest compressions due to failure in recognizing and correcting a malposition of the device may counteract a potential benefit of mechanical chest compressions. © 2011 Elsevier Ireland Ltd. All rights reserved.
1. Introduction It is estimated that approximately 275,000 cardiac arrests are treated by emergency medical services annually in Europe, with 10.7% survival to hospital discharge.1 A similar survival proportion of 8.4% is reported from the United States.2 Recent guidelines in cardiopulmonary resuscitation (CPR) state the importance of chest compression quality, including reducing the time without compressions (no-flow time) during CPR.3,4 Despite this, both in-hospital and out of hospital studies have indi-
夽 A Spanish translated version of the abstract of this article appears as Appendix in the final online version at doi:10.1016/j.resuscitation.2011.06.002. ∗ Corresponding author at: Department of Surgical Sciences - Anesthesiology & Intensive Care, Uppsala University, SE-751 85 Uppsala, Sweden. Tel.: +46 18 6110000; fax: +46 18 559357. E-mail addresses: [email protected] (H. Blomberg), [email protected] (R. Gedeborg), [email protected] (L. Berglund), [email protected] (R. Karlsten), [email protected] (J. Johansson). 0300-9572/$ – see front matter © 2011 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.resuscitation.2011.06.002
cated suboptimal chest compressions and undesirably long no-flow times.5–7 The importance of correct performance of compressions has been demonstrated in both animal studies and human studies.8–11 Both increased compression depth and lowered noflow time are associated with increased likelihood of defibrillation success in clinical studies.12,13 Several mechanical compression devices are now available on the market but it is unknown if they increase survival rate.14–19 Studies of new devices, drugs and protocols in CPR are often performed in well-defined laboratory settings during predefined periods of time, and with a selected and dedicated staff given specific training. This may explain why subsequent evaluation of actual performance and outcome after implementation in routine clinical practice can yield conflicting results.20 There are few studies on the quality of performance when mechanical compression devices are used in routine clinical practice and how this influences other interventions (e.g. ventilation and time to defibrillation) during CPR.21 The objective of the present manikin study was to evaluate the CPR performance of ambulance crews, who had a mechanical chest compression device implemented in their routine clinical practice.
H. Blomberg et al. / Resuscitation 82 (2011) 1332–1337
Manual compressions
6
Mechanical compressions
Compression depth (cm)
LUCAS out of position
5
1333
Correction of LUCAS position
Defibrillation
4 3.8
Defibrillation
Defibrillation
3 2 1 0
0
150
300
Seconds
450
600
Fig. 1. A sample registration of one ambulance crew performing LUCAS-CPR. In this case mechanical compressions are started after 170 s of CPR. Initially the compression depths are adequate (>3.8 cm), but LUCAS is sliding out of position resulting in shallow compressions. After a delayed correction, adequate compression depths are reestablished.
Two specific hypotheses were tested in this comparison of CPR with a mechanical device to CPR with manual compressions only: (i) that the use of the mechanical device delays first defibrillation and (ii) that the use of the mechanical device increases no-flow time until the first defibrillation. To accomplish this we conducted a randomized, crossover study in ambulance crews that have incorporated a mechanical compression device in their standard treatment protocol for CPR. Full-scale CPR scenarios in a manikin setup were used in order resemble CPR in clinical practice. 2. Methods 2.1. Study population The following criteria were used to select a Swedish ambulance organization suitable for the study: (a) it should not be connected to the investigators’ own organization, (b) a mechanical compression device should be a part of the standard treatment of cardiac arrest and incorporated in regular practice, (c) the organization should use the mechanical compression device as a pure replacement for manual compressions, and (d) the ambulance organization should not be involved in any studies concerning CPR. Based on these criteria, an ambulance organization with 160 employees working at six different ambulance stations was approached. The staff consisted of 72% nurses and 28% emergency medical technician equivalents (EMT equivalents; a nursing assistant with special ambulance training comparable to a paramedic education). The mechanical compression device LUCAS (Lund University Cardiopulmonary Assist System, Jolife AB, Lund, Sweden) had been utilized for 8 months. The organization had two different protocols for CPR; one for LUCAS-CPR used in ambulances equipped with the mechanical device and one for manual CPR in the other ambulances. As a part of their standard CPR-protocol with LUCAS, manual compressions were performed until the LUCAS device was applied. As mandatory in Sweden each ambulance was staffed with at least one nurse, authorized to perform advanced life support according to the 2005 ERC-guidelines with the recommended compression rate of 100 min−1 , depth of 4–5 cm and minimizing the no-flow time.22 The staff received centralized training and certification in CPR two times every 3 years, complemented by locally
arranged CPR training two times a year. With the introduction of LUCAS there was a 4-h hands-on training program in CPR with LUCAS with an instructor from the manufacturer, complemented by at least one local training session. The training program focuses on application of the device, correct positioning and the use of a stabilization strap. By randomly drawing employee identity numbers, unique for each of the 160 employees, 54 nurses and EMT equivalents forming 27 crews were selected. In case of two EMTs one was by randomization replaced, generating at least one nurse in each crew. Seven crew members could not attend as required. One of them was replaced without randomization, giving a total of 24 crews entering the study. No additional training in CPR was provided before the study. The participants were not informed about the hypotheses of the study. The need for ethical approval was waived by the Regional Ethical Review Board. 2.2. Study design Each crew served as their own control performing two 10min full CPR scenarios according to their ordinary CPR-protocol; one scenario with the aid of LUCAS (LUCAS-CPR) and one identical scenario but with only manual compressions (manual CPR). The crews were given written and verbal information about the study setup. A random selection with sealed envelopes determined which scenario to perform first. The following scenario was presented: “Sudden unconsciousness of a 45-year-old male. On your arrival more than five minutes have elapsed. You will find neither pulse nor respiration and no bystander CPR has been performed. No signs of trauma.” After the first scenario the crews were given 30 min rest, and then an identical CPR scenario was presented but a crossover to the other type of chest compression protocol was done. A computerized manikin (Resusci Anne Simulator, Laerdal Medical, Stavanger, Norway) was used with software developed by Jolife AB, Lund, Sweden. The manikin was modified by Jolife AB to accept venous cannulation and advanced airway management, and to measure compression depths more accurately (±0.1 cm) within a radius of 5 cm. Chest compression frequency and depth were automatically recorded. Fig. 1 illustrates one LUCAS-CPR registration in a condensed format.
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H. Blomberg et al. / Resuscitation 82 (2011) 1332–1337 Table 1 Demographics of the 42 individual crew members.
Key interventions, such as pulse check, first chest compression, defibrillation, drug administrations, and when applicable: first mechanical compression, application of stabilization strap, and correction of LUCAS position were manually tagged in the computerized log. Video recording was used for retrospective verification. The ECG simulator was set on refractory ventricular fibrillation throughout the experiment.
Age, years 39 (35–46) Gender, n (%) Male 30 (71) 12 (29) Female Basic medical education, n (%) 11 (26) Emergency medical technician equivalent 31 (74) Registered nurse 137 (71–230) Experience in prehospital care, months Number of performed training sessions in CPR 11 (7–20) With manual chest compressions 3 (2–4) With the LUCAS device Number of weeks since last training session in CPR 3 (2–24) With manual compressions 3 (1–9) With the LUCAS device Number of performed CPRs in clinical practice 25 (16–50) With manual chest compressions 2 (1–3) With the LUCAS device Number of weeks since last performance of CPR in clinical practice 20 (10–32) With manual chest compressions 12 (4–52) With the LUCAS device
2.3. Definitions According to an international consensus working group, compression depths ≥3.8 cm were considered as adequate.23 No-flow time was defined as intervals of more than 1.5 s without compressions. No-flow fraction was defined as no-flow time during a specified interval divided by the total time of this interval. 2.4. Description of the mechanical compression device, LUCAS
Continuous variables are given as median with interquartile range (IQR).
LUCAS is a battery driven rechargeable chest compression device. A piston with a suction cup made of silicon rubber delivers compressions with depths of 4–5 cm. The frequency of the compressions is 100 ± 5 min−1 . In between every 30th compression there is a 3-s pause allowing ventilation. The piston is adjusted vertically so that the suction cup is just in contact with the chest wall and in the horizontal plane the lower edge of the suction cup should be immediately above the distal end of the sternum. To avoid sliding, a stabilization strap is wrapped around the shoulders.
calculated using a bootstrap procedure with 1,000 replications and the percentile method. The statistical packages SAS version 9 (SAS Institute Inc., Cary, NC, USA), Stata/SE 11.0 (StataCorp, College Station, TX), and R version 2.7.0 (R Foundation for Statistical Computing, Vienna, Austria) were used for statistical analyses. Results are presented either as mean with 95% confidence interval or median with Inter Quartile Range (IQR) as appropriate. Since the hypothesis included two primary endpoints a p-value of less than 0.025 was considered statistically significant (Bonferroni correction).
2.5. Statistical methods A sample size calculation was performed under the assumption that a difference of 30 s in time to first defibrillation or a 5% difference in no-flow time until first defibrillation would be clinically important.24–27 For both of these primary endpoints, correlation between the two repeated measurements of the same ambulance crew was assumed to be 0.5. It was then estimated that a total of 48 scenarios (24 ambulance crews performing two scenarios) would be sufficient to detect differences of that magnitude with at least 80% power. The Shapiro Wilks W-statistic indicated that the primary endpoints were non-normally distributed even after logarithmic transformation (W-statistic <0.95). Treatment groups were therefore compared using the Wilcoxon matched pairs signed rank test. No carry over effects interfered with this test.28 Confidence intervals for the mean differences between the treatments were
3. Results Three out of the 24 ambulance crews were excluded; one crew because of technical problems such that data sampling was not possible and two crews failed to appear due to illness. The individual profiles of the remaining 42 ambulance crew members are presented in Table 1. There was no substantial difference in time to first defibrillation (manual CPR 178 s, versus LUCAS-CPR 182 s, p = 0.56), or the noflow time prior to first defibrillation (73 s versus 79 s, p = 0.04), see Table 2. There was no difference in no-flow fraction, either prior to first defibrillation or for the whole scenario (Table 2). There were differences in the compression quality when using LUCAS compared to manual compressions (Table 3). For the whole
Table 2 Time to 1st defibrillation, no-flow, frequencies and time to key interventions.
Time to 1st defibrillation (s) No-flow time until 1st defibrillation (s) No-flow time for the whole scenario (s) No-flow fraction (%) Prior 1st defibrillation For the whole scenario Compression frequency (min−1 ) Prior 1st defibrillation For the whole scenario Time to performed (s) First chest compression First ventilation mouth to mask First ventilation on laryngeal mask Intravenous cannulation First administration of adrenaline
CPR with mechanical compression aid (LUCAS-CPR)
CPR without mechanical compression aid (manual CPR)
Mean difference
182 79 181
178 73 200
4 6 −20
44 30
41 33
3 −3
118 104
128 129
−10 −25
−15 to 5 −29 to −20
15 66 231 206 503
13 57 293 106 494
1 9 −62 100 9
−1 to 3 −17 to 30 −114 to −11 79 to 123 −8 to 29
95% confidence interval
p-Value
−12 to 21 0 to 12 −36 to 1
0.56 0.04
0 to 6 −6 to 0
Presented as the mean difference between LUCAS-CPR and manual CPR, 95% confidence interval for the difference, and p-value for the primary endpoints.
H. Blomberg et al. / Resuscitation 82 (2011) 1332–1337
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Table 3 Adequacy of compressions.
Compressions prior to 1st defibrillation Total number of compressions, n Fraction of adequatea compressions (%) Number of manual compressions Fraction of adequatea manual compressions (%) Number of mechanical compressions Fractions of adequatea mechanical compressions (%) Compressions during the whole scenario Total number of compressions Fraction of adequatea compressions (%) Number of manual compressions Fraction of adequatea manual compressions (%) Number of mechanical compressions Fractions of adequatea mechanical compressions (%)
CPR with mechanical compression aid (LUCAS-CPR)
CPR without mechanical compression aid (manual CPR)
Mean difference
95% confidence interval
199 71% 114b 89%b 85 46%
221 94% 221 94%
−21 −23%
−48 to 1 −37% to −8%
732 58% 116b 88%b 617 52%
856 88% 856 88%
−124 −30%
−5%
0%
−12% to 3%
−155 to −91 −50% to −13% −9% to 7%
Presented as the mean difference between LUCAS-CPR and manual CPR and 95% confidence interval for the difference. a Adequate compression defined as compression depth ≥3.8 cm. b The manual compressions in LUCAS-CPR is done before the application of the mechanical device.
scenario, the number of adequate compressions in manual CPR was 78% higher in relation to LUCAS-CPR (750 versus 422). Analyzing adequate compressions as a fraction of the total number of chest compressions in order to minimize the influence of the higher compression rate during manual CPR gave similar results. Manual CPR was associated with a higher fraction of adequate compressions than LUCAS-CPR (Fig. 2). The median compression depth for mechanical compressions was 3.8 (IQR 3.7–4.6) and for manual compressions 4.7 (IQR 4.5–5.0). In LUCAS-CPR, median time to first mechanical compression was 100 s (IQR 91–132). Correction of a malposition of LUCAS was done by five ambulance crews (24%), as verified by video review, with a median time from the first inadequate compression to correction of 241 s (IQR 197–371). In one case the correction was insufficient, i.e. not leading to adequate compressions after the correction. The video recording also documented that in LUCAS-CPR only 12 out of the 21 ambulance crews (57%) applied the stabilization strap on the LUCAS device. The median time from first mechanical compression to application of the strap was 249 s (IQR 135–321). 3.1. Performance of mechanical compressions in relation to educational level and professional experience The fraction of adequate mechanical compressions did not differ depending on the level of education of the crews (51% with two nurses versus 50% with one nurse and one EMT, 95% CI for
difference: −37% to 39%). The results did not indicate substantial correlations between the fraction of adequate mechanical compressions and any of the following factors: number of performed training sessions using LUCAS-CPR (correlation coefficient −0.05, 95% CI −0.47 to 0.39), number of performed LUCAS-CPR in clinical practice (correlation coefficient 0.02, 95% CI −0.41 to 0.45), time since last training session using LUCAS-CPR (correlation coefficient −0.16, 95% CI −0.55 to 0.30) or time since last performed LUCASCPR in clinical practice (correlation coefficient 0.17, 95% CI −0.29 to 0.53).
4. Discussion Our results indicate that the incorporation of a mechanical compression device in the CPR algorithm is possible without prolonging time to first defibrillation or substantially increasing no-flow time in the early phase of CPR. There was, however, a remarkably poor quality of compressions with the use of the mechanical device. This study was designed as a cross-over trial in order to reduce the influence of variation in performance between the ambulance crews. As indicated by the confidence intervals, the study had sufficient power to detect clinically meaningful differences in the primary endpoints of the study. The cross-over design in combination with a representative study population using an implemented new device contributes to the strength of the study.
Fig. 2. Panel A shows fraction of adequate compressions until 1st defibrillation. Panel B shows fraction of adequate compressions during the whole scenario of 10 min. Each line connects one crew’s results in LUCAS-CPR and manual CPR. Box-and-whisker plots for LUCAS-CPR and manual CPR, respectively. Boxes representing IQR, () median, whiskers representing max and min value (values more than three interquartile distances away from the median are considered outliers and are marked with dots).
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The strikingly poor quality of compressions with the mechanical device has several possible explanations. Incorrect application of LUCAS in the vertical plane, with a space between the piston and the chest wall, will generate too shallow compressions. Inappropriate horizontal position of LUCAS relative to the sternum, which could be due to either incorrect initial application or by sliding of the device during ongoing compressions, will generate misplaced and inadequate compressions. For unknown reasons, almost half of the ambulance crews neglected to apply the stabilization strap to the LUCAS device, and when applied, it was done with a substantial time delay. The sliding of LUCAS is a known phenomenon in clinical practice and therefore the usage of the stabilization strap is emphasized in the training program for the device.14 Sliding of the LUCAS device in clinical practice may be less common than in the manikin setting since the manikin is lighter than a human being and has a surface different from skin. This can, however, not explain failure to apply the stabilization strap or failure to observe and correct the position when sliding of the device occurred. Although malposition and/or sliding of the mechanical device were clearly verified by video review, objective measurements would certainly have been desirable. This would, however, have interfered with the continuation of the crews’ performance. The manikin setting may limit generalizability to clinical CPR. Even though our manikin had been modified to increase tolerance to malpositioned compressions, measurements of compression depth may be biased. ERC-guidelines clearly state the importance of correct positioning and adequate depths of compressions but the consequences of compressions classified as “not adequate” in the manikin setting are unknown for patient outcome in the clinical situation. Although animal studies indicate superior compression quality from mechanical compression devices,8,29 our study highlights the importance of quality control of performance after clinical implementation. An interesting observation was that airway management seemed to be prioritized when LUCAS is used, while intravenous access seemed to be prioritized when performing manual compressions. There was no correlation between time since last LUCAS-CPRtraining and quality of mechanical compressions. Little is known about skill retention over time in CPR training, but earlier studies suggest an interval of no more than 3–6 months between refresher courses.30 Thus, it is unlikely that the average of 3 weeks since last practice in this study population could explain the poor performance when using the mechanical compression device. A potential limitation of this study is that the artificial simulator setting may not reflect the performance of CPR in the clinical setting. The general conditions for CPR were unnaturally optimal in the study setting. The simulation setting might influence the incentive of the ambulance crew to perform their best. However, the quality of manual compressions and the performance of key interventions were comparable to previous studies in clinical settings indicating adequate overall performance from the studied crews.5,31 This study was performed on one single ambulance organization and the question of generalizability of the results must therefore be addressed. The criteria used for selecting the study population and the random selection of individuals was intended to select medical staff as representative as possible of an average Swedish ambulance organization. The fact that adherence to CPR guidelines in the study in terms of key interventions and quality of manual compressions were similar to results from other settings indicates that education and/or skill in CPR are representative of other ambulance organizations as well.5,31 Nevertheless, the quality of educational programs and instructor competence is an important aspect.32,33 Results from a multicentre study using another mechanical compression device (Autopulse) revealed a substantial variability in CPR performance with the mechanical device, despite a standardized
educational program.34 These results corroborate those of the present study. Mechanical devices for cardiac compressions are being implemented in routine clinical practice in spite of limited evidence to support their use from clinical outcome studies.18,19 Intuitively, these devices have obvious advantages. They enable the crew to be seated with safety belt applied while performing CPR during transport (as opposed to performance of manual compressions) and increase their ability to perform other important interventions due to alleviated workload.14 The devices also provide consistent compression rate and allow defibrillation during ongoing chest compressions. Some studies suggest improved CPR in special settings, such as catheter lab and during flights.35–37 However, our study indicates that there are still questions concerning the quality of chest compressions after widespread implementation of the device in clinical practice. Auditory real-time feedback utilized in automated external defibrillators could possibly be applied to mechanical compression devices as well.38 Previous clinical studies have failed to evaluate the adequacy of compression depth generated by the mechanical device.14,16,39 The device certainly delivers compressions with a constant depth. However, due to incorrect initial placement or sliding, it doesn’t necessarily generate adequate compression depth. If the poor compression quality found in this study reflects the performance in the clinical setting, this might partly explain failure to improve outcome in clinical trials. This study supports that study protocols should be optimized during simulations before launching large multicentre trials and that the quality of both manual and mechanical compressions should be evaluated in clinical studies.34 Furthermore, there is a need for clinical studies with focus on application and the feasibility of mechanical devices. The study was performed according to the 2005 AHA-guidelines. In the recently published 2010 AHA-guidelines the importance of adequate compression depth is further emphasized. The recommended depth of compression has increased from 1.5–2 in. to at least 2 in.40 These changes could be a potential limitation of the study but we have no reason to believe that the results would be substantially different if the study would have been performed after implementation of the 2010 AHA-guidelines. Our results support the 2010 AHA-guidelines which states that there is no evidence to recommend mechanical chest compression devices for routine clinical use41 but our results also imply that it is of utmost importance to ensure appropriate use of the device before evaluating the potential benefit in clinical trials. 5. Conclusion The study could not show that the use of the mechanical compression aid caused clinically meaningful differences in time to first defibrillation or no-flow time in the early phase of CPR. However, constant but poor chest compressions due to failure in recognizing and correcting a malposition of the device may erase a potential benefit of mechanical chest compressions. Further work is needed on how to assure the correct usage of mechanical chest compression devices before clinical evaluation and potential implementation in clinical practice. Conflict of interest statement Jolife AB provided the manikin and related technical support but was not involved in the design of the study, statistical analysis, interpretation of the results or the writing of the manuscript. Rolf Karlsten has once received a personal consultant fee from Jolife AB. All other authors declare that they have no financial or other conflicts of interest.
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