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Push-fast recommendation on performing CPR causes excessive chest compression rates, a manikin model
American Journal of Emergency Medicine 32 (2014) 1455–1459
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Original Contribution
Push-fast recommendation on performing CPR causes excessive chest compression rates, a manikin model☆,☆☆ Ming-Yuan Hong, MD a, Jui-Yi Tsou, PhD b, Pai-Chin Tsao, MS c, Chih-Jan Chang, MD a, Hsiang-Chin Hsu, MD, MS a, Tsung-Yu Chan, MD a, Sheng-Hsiang Lin, PhD d, Chih-Hsien Chi, MD a,⁎, Fong-Chin Su, PhD c a
Department of Emergency Medicine, National Cheng Kung University, Tainan, Taiwan Department of Physical Therapy, Fooyin University, Kaohsiung, Taiwan c Institute of Biomedical Engineering, National Cheng Kung University, Tainan, Taiwan d Research Center of Clinical Medicine, College of Medicine, National Cheng Kung University, Tainan, Taiwan b
a r t i c l e
i n f o
Article history: Received 3 May 2014 Received in revised form 25 August 2014 Accepted 28 August 2014
a b s t r a c t Background: Increasing chest compression rate during cardiopulmonary resuscitation can affect the workload and, ultimately, the quality of chest compression. This study examines the effects of compression at the rate of as-fast-as-you-can on cardiopulmonary resuscitation (CPR) performance. Methods: A crossover, randomized-to-order design was used. Each participant performed chest compressions without ventilation on a manikin with 2 compression rates: 100 per minute (100-cpm) and “push as-fast-as you-can” (PF). The participants performed chest compressions at a rate of either 100-cpm or PF and subsequently switched to the other after a 50-minute rest. Results: Forty-two CPR-qualified nonprofessionals voluntarily participated in the study. During the PF session, the rescuers performed CPR with higher compression rates (156.8 vs 101.6 cpm), more compressions (787.2 vs 510.8 per 5 minutes), and more duty cycles (51.0% vs 41.7%), but a lower percentage of effective compressions (47.7% vs 57.9%) and a lower compression depth (35.6 vs 38.0 mm) than they did during the 100-cpm session. The CPR quality deteriorated in numbers and percentile of effective compression since the third minute in the PF session and the fourth minute in the 100-cpm session. The percentile of compressions with adequate depth in the 100cpm sessions was higher than that in the PF sessions during the second, third, and fourth minutes of CPR. Conclusion: Push-fast technique showed a significant decrease in the percentile of effective chest compression compared with the 100-cpm technique during the 5-minute hand-only CPR. The PF technique exhibited a trend toward increased fatigue in the rescuers, which can result in early decay of CPR quality. © 2014 Elsevier Inc. All rights reserved.
1. Introduction Effective chest compressions are essential for providing blood flow during cardiopulmonary resuscitation (CPR). A key principle in resuscitation is early CPR with an emphasis on chest compressions [1]. Human and animal studies have revealed that chest compression rate influences CPR success rate and outcome [2]. Any technique that diminishes or avoids interrupting chest compressions improves CPR outcome. Interrupting chest compressions for rescue breathing during CPR for
☆ Conflict of interest statement: All of the authors have no conflicts of interest to declare. ☆☆ Grants: National Science Council of the Republic of China, Taiwan (contract no. NSC 98-2320-B-006-001). ⁎ Corresponding author. Department of Emergency Medicine, Medical College and Hospital, National Cheng Kung University, Tainan 70403, Taiwan. Tel./fax: + 886 6 2766120. E-mail address: [email protected] (C.-H. Chi). http://dx.doi.org/10.1016/j.ajem.2014.08.074 0735-6757/© 2014 Elsevier Inc. All rights reserved.
ventricular fibrillation cardiac arrest produces adverse hemodynamic effects [3]. Increasing chest compression fraction is associated with survival benefit in patients who experienced out-of-hospital ventricular fibrillation [4]. Even with optimal compression depth and hand position, suboptimal compression rates affect the effectiveness of resuscitation [5]. Continual chest compression improved the outcome during a simulated single nonprofessional rescuer scenario [6]. Clinical studies focused on patients experiencing out-of-hospital cardiac arrest have revealed that hand-only CPR (chest compression alone) showed similar survival outcomes, compared with standard CPR (chest compression with mouth-to-mouth ventilation) [7,8]. However, the optimal rate of chest compression is unknown. Although the 2010 version of the American Heart Association (AHA) Guidelines for CPR [9] recommends that all rescuers provide effective chest compressions, push hard and push fast, at a rate of at least 100 cpm without an upper limit, the 2010 European Resuscitation Council CPR guidelines [10] recommend an upper limit of 120 cpm.
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Although increasing the compression rate can improve patient survival [11], it can influence the workload and the rate of rescuer fatigue and the quality of CPR [9,12]. In this study, we investigated and measured the effects of continual compression rates on a manikin. We hypothesized that different compression rates create differences in performance outcomes and the physiological parameters and fatigue of rescuers.
2. Materials and methods 2.1. Study design This experiment was conducted using a crossover, randomized-toorder design. The study was approved by the institute's human ethics committee. All participants provided informed written consent.
2.5. Data analysis Statistical analyses were performed using the SPSS for Windows (SPSS, Chicago, IL), version 17.0. Continuous variables, including age, height, body weight, chest compression data, physical variables, and VAS, were expressed as the mean ± SD. Chest compression rate, effective compression numbers during each minute of the study, chest compression data, physiologic variables, and perceived exertion scale between PF and 100-cpm protocols were analyzed using a paired t test. We also conducted a subgroup analysis separately for female and male participants. As for the compression performance for each minute, the compression performance between each minute was analyzed using 1-way analysis of variance analysis, and compression performance between 100-cpm and PF section was analyzed using a paired t test. The main effect was significant, as defined by P b .05. 3. Results
2.2. Study protocol
3.1. Chest compression data during 5 minutes of CPR
The participants had no muscular skeletal injuries, sprains, or pain. No food was eaten 30 minutes before tests. Alcohol, tea, and coffee were prohibited on the test days. The participants practiced CPR on manikins before they began the tests. Effective chest compression was identified as chest compressions with a depth of more than or equal to 38 mm. Each participant subsequently performed continual external chest compressions at 2 compression rates on a Resusci Anne manikin (Laerdal Medical, Wappingers Falls, NY): 100-cpm (ie, continual external chest compressions without interrupting ventilations at a rate of 100 per min [100-cpm]) and the push-fast (PF) rate (ie, continual external chest compressions without interrupting ventilations at the asfast-as-you-can rate). The chest compression duration was 5 minutes for each session, alternating with interrupted rest periods of 50 minutes. The 5-minute chest compression involved a single nonprofessional rescuer performing occasionally for 5 minutes during a real cardiac arrest. This scenario was used in our previous study and in a study on the efficacy decay in CPR [13-15]. The order of the compression sessions was randomized.
From January to July 2010, 42 CPR-certified rescuers voluntarily participated in the study. Among them, 21 were women. The mean age of the rescuers was 24.8 ± 6.3 years, the mean height was 166.5 ± 7.5 cm, and the mean weight was 63.3 ± 13.6 kg. Table 1 shows chest compression data obtained from the Laerdal PC SkillReporting System for 5 minutes of external chest compressions. According to the power analysis for a paired t test, a sample size of 42 subjects had a reasonable power (1.00) to distinguish the 2 sessions of CPR based on compression rates. During the PF session, the rescuers performed CPR with higher compression rates, more compressions, more duty cycles, and a lower percentage of effective compressions and lower compression depths than they did during the 100-cpm session. We observed no differences in rescuer performance in incomplete release during the PF and 100cpm sessions.
2.3. Work while performing external cardiac compression Physical parameters, including heart rate, blood pressure, and oxygen saturation, were measured for each study participant before and after each CPR session. The measured variables were estimated maximum heart rate (EMHR = 220 − age) and heart rate as a percentage of EMHR at the end of each CPR. The visual analog scale (VAS) was used to rank the intensity of exercise across a continuum from 0 “none” to 10 “extreme exhaustion.” The participants rated how they felt before and after each CPR. After performing both sessions, they were asked “Which session is more exhausting: 100-cpm or PF?”
2.4. Performance of chest compression on the manikin Our experimental model consisted of a Laerdal Skillmeter ResusciAnne manikin located on the floor; performers kneeled beside the manikin's chest to mimic typical bystander resuscitations. The manikin was connected to a laptop computer, and external chest compression performance data were transmitted from the manikin to the computer. Data were collected using the Laerdal PC SkillReporting System (PC Skillmeter; Laerdal Medical, Stavanger, Norway). Data output from the Laerdal PC SkillReporting System included average compression rate, average compression depth, average duty cycle, total compressions counted, compressions registered with adequate depth, and compressions registered with incomplete release.
3.2. Rate of chest compressions Figure A shows the compression rate in the 100-cpm and PF sessions over the 5-minute period. The compression rates for each minute from the first to fifth minute were 158.1 ± 23.7, 152.3 ± 21.2, 154.7 ± 22.3, 158.3 ± 22.4, and 160.1 ± 23.6 per minute in the PF session and 99.0 ± 7.3, 101.0 ± 3.7, 102.0 ± 5.7, 103.2 ± 6.9, and 103.5 ± 7.6 per minute in the 100-cpm session. In subgroup analysis, we conducted analyses separately in female or male participants in the compression rates at each minute (Supplemental Figure A). The compression rate in the PF session was higher than that in the 100-cpm session. 3.3. Count of effective chest compressions Figure B shows the counts of chest compression with adequate depth. The counts of effective chest compressions for each minute from the first to fifth minute were 112.7 ± 58.8, 78.8 ± 68.2, 61.8 ± 69.2, 57.8 ± 70.3, and 56.1 ± 69.3 in the PF session and 78.0 ± 33.0, 65.1 ± 41.0, 54.7 ± 41.7, 49.1 ± 43.9, and 46.0 ± 44.1 in the 100-cpm session. The counts of effective chest compression deteriorated over time, and the deterioration was observed beginning in the third minute of the PF session and the fourth minute of the 100-cpm session. The counts of adequate compressions in the PF session were higher than those in the 100-cpm session were during the first minute. We observed no significant differences in the counts of adequate compression in the second to fifth minutes. We perform subgroup analyses separately for female or male participants in the counts of adequate compressions at each minute (Supplemental Figure B). The counts of effective chest compression deteriorated over time, and the deterioration was observed predominantly in the PF session in both genders.
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Table 1 Chest compression data during 5 minutes of CPR
Compression rate (per minute) Count of compressions/5 min Compression depth (mm) Percent of effective compressions (%) Count of effective compression/5 min Incomplete release (%) Duty cycle (%)
100-cpm
PF
101.6 ± 4.8 510.8 ± 24.2 38.0 ± 8.1 57.9 ± 36.4 292.9 ± 187.1 8.4 ± 24.8 41.7 ± 6.6
156.8 ± 21.7 787.2 ± 108.9 35.6 ± 12.4 47.7 ± 40.2 367.1 ± 310.3 6.9 ± 18.0 51.0 ± 5.6
Mean difference (95% CI) −55.2 (−62.1, −48.3)⁎⁎ −276.4 (−311.2, −241.7)⁎⁎ 2.4 (0.0, 4.8)⁎ 10.1 (2.3, 17.7)⁎ −74.2 (−137.7, −10.6)⁎ 1.5 (−3.8, 6.8) −9.2 (−11.5, -7.0)⁎⁎
Data were given as mean ± SD or mean difference (95% confidence interval). Abbreviation: CI, confidence interval. ⁎ P b .05. ⁎⁎ P b .001.
3.4. Percentile of effective chest compressions Figure C shows the percentile of effective chest compression between the 2 sessions. The percentile of effective compression for each minute from the first to fifth minute was 72.5 ± 36.5, 52.8 ± 44.9, 40.8 ± 45.6, 37.3 ± 45.4, and 36.1 ± 44.8 in the PF session and 77.5 ± 32.0, 64.6 ± 41.1, 54.4 ± 41.5, 48.5 ± 43.4, and 45.5 ± 43.5 in the 100-cpm session. The percentile of effective compressions deteriorated over time, showing an earlier percentile of effective chest compression
deterioration in the PF session than in the 100-cpm session (deterioration was noted from the third minute in the PF session vs the fourth minute in the 100-cpm session). The percentile of effective chest compression in the 100-cpm sessions was higher than that in the PF sessions during the second, third, and fourth minutes of CPR. We conducted subgroup analyses separately in female or male participants in the percentile of adequate compressions at each minute (Supplemental Figure C). The deteriorated percentile of effective chest compression was more predominant in the PF session than that in the 100-cpm session in both sexes. 3.5. Physiologic variables and perceived exertion Table 2 shows the physiologic variables and perceived exertion of rescuers measured after both sessions of CPR. We observed no difference in physiologic variables and VAS before the PF and 100-cpm sessions of CPR (data not shown). A comparison of physiological parameters after each session showed that the heart rate, estimated maximal heart rate, and VAS were significantly higher after rescuers finished the PF session than that after the 100-cpm session. No differences were evident in systolic blood pressure, mean arterial pressure, and oxygen saturation after 2 sessions of CPR. The questionnaire response revealed that chest compression at the PF rate was more exhausting than at the rate of 100 cpm for 38 participants (90.5%) and 100-cpm was more exhausting for 4 participants (9.5%). 4. Discussion 4.1. Summary of main findings The AHA recommends chest compression at the rate of as-fast-asyou-can, but the influence on CPR performance is unknown. We evaluated the effect of various compression rates of hands-only CPR, “push fast,” and 100-cpm on CPR quality and performer fatigue among nonprofessional rescuers. The features of the recommended PF technique were excessive compression rates more than 150 cpm and early deterioration in counts and percentile of effective compressions, compared with chest compression at a rate of 100 cpm. Rescuer fatigue was the Table 2 Physiologic variables and perceived exertion after external chest compressions
SBP (mm Hg) MAP (mm Hg) SpO2 (%) HR (per minute) %EMHR VAS Figure. The CPR performance of each minute was shown as mean, including count of chest compression (A), count of effective chest compression (B), and the percentile of effective chest compression (C). Data were given as mean. ⁎P b .05 compared to the CPR performance of100-cpm at indicated time; #P b .05 compared to the CPR performance of the first minute.
100-cpm
PF
125.4 ± 23.7 93.9 ± 14.9 96.9 ± 1.4 112.8 ± 23.3 57.7 ± 11.2 4.8 ± 2.1
129.2 ± 15.7 95.1 ± 12.9 97.0 ± 1.2 124.3 ± 20.8 63.6 ± 10.2 6.2 ± 2.1
Mean difference (95% CI) −3.8 (−10.3, 2.7) −1.2 (−4.9, 2.5) 0.0 (−0.5, 4.7) −11.5 (−18.8, −4.1)⁎ −5.9 (−9.7, −2.2)⁎ −1.5 (−2.1, −0.8)⁎⁎
Data were given as mean ± SD or mean difference (95% confidence interval). Abbreviations: SBP, systolic blood pressure; MAP, mean arterial pressure; SpO2, saturation O2; HR, hear rate; %EMHR, percentages of estimated maximum heart rate. ⁎ P b .01. ⁎⁎ P b .001.
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primary cause of deterioration in CPR efficacy, and the recommended PF technique showed a trend toward increased effort loading in the rescuers, compared with the 100-cpm rate. The optimal rate of chest compression remains unknown. According to the 2010 version of the AHA Guidelines for CPR, all rescuers should provide effective compressions at a rate of at least 100 pm without an upper rate limit [9]. However, the 2010 European Resuscitation Council CPR guidelines [10] recommend an upper rate limit of 120 cpm. Abella et al [5] showed a higher chest compression rate associated with a higher rate of return of spontaneous circulation. The mean chest compression rates for initial survivors were 90 ± 17 cpm and 79 ± 18 cpm for nonsurvivors. Idris et al [16] reported a relationship between chest compression rates and outcomes for cardiac arrest. The cubic spline curve for rate of return of spontaneous circulation peaked at a compression rate of 125 cpm and subsequently declined. Monsieurs et al [17] reported that excessive compression rates may lead to insufficient depth of compression. Consistent with the works of Idris et al and Monsieurs et al, our study revealed that the AHA guideline for the “asfast-as-you-can” compression rate resulted in an excessive compression rate of approximately 150 cpm and loss of compression depth. The recommended duty cycles ranging from 20% to 50% account for adequate coronary and cerebral perfusion [9]. Our results showed that the duty cycles in both rates of chest compression were within the recommended range. Previous studies have observed an increase in duty cycle at a faster rate and a duty cycle near 50% at a compression rate of 160 beats per minute [18,19]. Our results revealed an increased duty cycle reaching the recommended 50% during the PF session. Consistent with the study of Hightower et al [13], although the participants maintained an adequate rate in chest compression, CPR efficacy declined with time. According to the count or percentile of effective compressions in the study, the efficacy deterioration was noticeable within 3 minutes after starting CPR in the PF session and within 4 minutes in the 100-cpm session. The PF technique exhibited a trend toward in early decay of CPR quality. Previous studies have used a higher number of compressions, and the ventilation ratio exhibited an increased number of adequate chest compressions and attempted chest compressions [20,21]. We also observed an increased number of total and effective compressions performed in the PF session during the 5-minute CPR. The analysis of each minute of CPR performance revealed that the counts of effective compression were higher during the first minute in the PF session than in the 100-cpm session. However, the rescuers performed a higher percentile of effective chest compression in the 100-cpm session than in the PF session during the 5-minute CPR. The percentile of effective chest compression was higher in the 100-cpm session than in the PF session in the second to fourth minutes. Although the as-fast-as-you-can compression rate provided a higher compression count in the first minute of CPR, no difference was detected in the percentile of effective chest compression during the first minute of CPR. Compared with a chest compression rate of as-fast-as-you-can, the compression rate of 100 cpm for the 5-minute CPR is likely to maintain adequate chest compression quality in the percentile of effective compression and compression depth. Furthermore, in subgroup analysis for female or male participants, the decreased percentile of effective chest compression was more predominant in the PF session than in the 100-cpm sessions in both genders. Rottenberg [22-24] has reported that typical male rescuers were taller and have more upper-body weight than female rescuers and, therefore, are more physically capable of providing effective CPR. Chung et al [25] also showed that the compression depth was associated with rescuers' body weight, height, and sexes during metronome-guided CPR. In the present study, the decay in counts or percentile of effective chest compression was noted respectively in the second minute of CPR in female participants and in the third minute in male participants. Consistently, the decay in efficacy of CPR was noted earlier in female than in male participants. It may be considered to develop CPR recommendations as well as dispatcher-assisted CPR
instructions according to physical capacity of the rescuers. Further studies may be designed to determine separately for men and women the most appropriate compressions rate or depth that is likely to facilitate effective CPR performance. Rescuer fatigue during CPR can cause inadequate depth and rates of chest compression. To avoid a decline of CPR quality, the AHA recommends rotating rescuers every 2 minutes [9]. An evaluation of the heart rate and subjective scales of perceived exertion suggests that increasing consecutive compressions can increase exercise intensity and affect rescuer fatigue [12,26,27]. We demonstrated that using the PF recommendation resulted in a greater workload, measured by physiological variables and self-reporting perceived effort after 5 minutes of chest compression. Rotating rescuers every 2 minutes is, therefore, reasonable to increase effective compressions when promoting the PF protocol. 4.2. Limitations This study had certain limitations. First, the outcome measures excluded crucial clinical variables, including patient survival and physiology variables of resuscitation during the manikin studies. For example, gasping is essential for effective CPR and is associated with favorable survival and neurologic outcome [28–30]. The manikin study cannot reveal the effect of gasping on the rescuers' CPR performance and the survival or neurologic outcome of patients. Second, the study population included CPR trained nonprofessional rescuers. Although PF CPR targets untrained rescuers, CPR-trained rescuers were more likely to provide CPR than were people without CPR training [31]. Therefore, extrapolating this finding to the untrained public warrants caution. Finally, the AHA and the European Resuscitation Council 2010 guideline have recommended a push depth of at least 5 cm [10]. Chest compression quality deteriorated substantially over the study period in both protocols, suggesting that a depth above 5 cm might be challenging for rescuers to accomplish. 5. Conclusion The AHA recommends that rescuers perform CPR at the push-asfast-as-you-can rate, but the optimal rate is unknown. We evaluated the effect of hands-only CPR, PF, and 100-cpm techniques on CPR quality and performer fatigue among nonprofessional rescuers. Although the PF technique showed increasing numbers of compressions delivered each minute, we observed a significant decrease in the percentile of effective chest compressions compared with the 100-cpm technique during the 5-minute hands-only CPR. The PF technique exhibited a trend toward increased fatigue in the rescuers and can result in a deterioration tendency in the percentile of effective compression during CPR. Further studies are required to evaluate the effect of the PF recommendation for faster chest compressions. Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.ajem.2014.08.074. Acknowledgment The authors thank the National Science Council of the Republic of China, Taiwan (contract no. NSC 98-2320-B-006-001). We are also grateful to Shang-Chi Lee, MSc, for providing statistical consulting services from the Biostatistics Consulting Center, Research Center of Clinical Medicine, National Cheng Kung University Hospital. References [1] Travers AH, Rea TD, Bobrow BJ, Edelson DP, Berg RA, Sayre MR, et al. Part 4: CPR overview: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation 2010;122(18 Suppl 3): S676–84.
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Original Contribution
Push-fast recommendation on performing CPR causes excessive chest compression rates, a manikin model☆,☆☆ Ming-Yuan Hong, MD a, Jui-Yi Tsou, PhD b, Pai-Chin Tsao, MS c, Chih-Jan Chang, MD a, Hsiang-Chin Hsu, MD, MS a, Tsung-Yu Chan, MD a, Sheng-Hsiang Lin, PhD d, Chih-Hsien Chi, MD a,⁎, Fong-Chin Su, PhD c a
Department of Emergency Medicine, National Cheng Kung University, Tainan, Taiwan Department of Physical Therapy, Fooyin University, Kaohsiung, Taiwan c Institute of Biomedical Engineering, National Cheng Kung University, Tainan, Taiwan d Research Center of Clinical Medicine, College of Medicine, National Cheng Kung University, Tainan, Taiwan b
a r t i c l e
i n f o
Article history: Received 3 May 2014 Received in revised form 25 August 2014 Accepted 28 August 2014
a b s t r a c t Background: Increasing chest compression rate during cardiopulmonary resuscitation can affect the workload and, ultimately, the quality of chest compression. This study examines the effects of compression at the rate of as-fast-as-you-can on cardiopulmonary resuscitation (CPR) performance. Methods: A crossover, randomized-to-order design was used. Each participant performed chest compressions without ventilation on a manikin with 2 compression rates: 100 per minute (100-cpm) and “push as-fast-as you-can” (PF). The participants performed chest compressions at a rate of either 100-cpm or PF and subsequently switched to the other after a 50-minute rest. Results: Forty-two CPR-qualified nonprofessionals voluntarily participated in the study. During the PF session, the rescuers performed CPR with higher compression rates (156.8 vs 101.6 cpm), more compressions (787.2 vs 510.8 per 5 minutes), and more duty cycles (51.0% vs 41.7%), but a lower percentage of effective compressions (47.7% vs 57.9%) and a lower compression depth (35.6 vs 38.0 mm) than they did during the 100-cpm session. The CPR quality deteriorated in numbers and percentile of effective compression since the third minute in the PF session and the fourth minute in the 100-cpm session. The percentile of compressions with adequate depth in the 100cpm sessions was higher than that in the PF sessions during the second, third, and fourth minutes of CPR. Conclusion: Push-fast technique showed a significant decrease in the percentile of effective chest compression compared with the 100-cpm technique during the 5-minute hand-only CPR. The PF technique exhibited a trend toward increased fatigue in the rescuers, which can result in early decay of CPR quality. © 2014 Elsevier Inc. All rights reserved.
1. Introduction Effective chest compressions are essential for providing blood flow during cardiopulmonary resuscitation (CPR). A key principle in resuscitation is early CPR with an emphasis on chest compressions [1]. Human and animal studies have revealed that chest compression rate influences CPR success rate and outcome [2]. Any technique that diminishes or avoids interrupting chest compressions improves CPR outcome. Interrupting chest compressions for rescue breathing during CPR for
☆ Conflict of interest statement: All of the authors have no conflicts of interest to declare. ☆☆ Grants: National Science Council of the Republic of China, Taiwan (contract no. NSC 98-2320-B-006-001). ⁎ Corresponding author. Department of Emergency Medicine, Medical College and Hospital, National Cheng Kung University, Tainan 70403, Taiwan. Tel./fax: + 886 6 2766120. E-mail address: [email protected] (C.-H. Chi). http://dx.doi.org/10.1016/j.ajem.2014.08.074 0735-6757/© 2014 Elsevier Inc. All rights reserved.
ventricular fibrillation cardiac arrest produces adverse hemodynamic effects [3]. Increasing chest compression fraction is associated with survival benefit in patients who experienced out-of-hospital ventricular fibrillation [4]. Even with optimal compression depth and hand position, suboptimal compression rates affect the effectiveness of resuscitation [5]. Continual chest compression improved the outcome during a simulated single nonprofessional rescuer scenario [6]. Clinical studies focused on patients experiencing out-of-hospital cardiac arrest have revealed that hand-only CPR (chest compression alone) showed similar survival outcomes, compared with standard CPR (chest compression with mouth-to-mouth ventilation) [7,8]. However, the optimal rate of chest compression is unknown. Although the 2010 version of the American Heart Association (AHA) Guidelines for CPR [9] recommends that all rescuers provide effective chest compressions, push hard and push fast, at a rate of at least 100 cpm without an upper limit, the 2010 European Resuscitation Council CPR guidelines [10] recommend an upper limit of 120 cpm.
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Although increasing the compression rate can improve patient survival [11], it can influence the workload and the rate of rescuer fatigue and the quality of CPR [9,12]. In this study, we investigated and measured the effects of continual compression rates on a manikin. We hypothesized that different compression rates create differences in performance outcomes and the physiological parameters and fatigue of rescuers.
2. Materials and methods 2.1. Study design This experiment was conducted using a crossover, randomized-toorder design. The study was approved by the institute's human ethics committee. All participants provided informed written consent.
2.5. Data analysis Statistical analyses were performed using the SPSS for Windows (SPSS, Chicago, IL), version 17.0. Continuous variables, including age, height, body weight, chest compression data, physical variables, and VAS, were expressed as the mean ± SD. Chest compression rate, effective compression numbers during each minute of the study, chest compression data, physiologic variables, and perceived exertion scale between PF and 100-cpm protocols were analyzed using a paired t test. We also conducted a subgroup analysis separately for female and male participants. As for the compression performance for each minute, the compression performance between each minute was analyzed using 1-way analysis of variance analysis, and compression performance between 100-cpm and PF section was analyzed using a paired t test. The main effect was significant, as defined by P b .05. 3. Results
2.2. Study protocol
3.1. Chest compression data during 5 minutes of CPR
The participants had no muscular skeletal injuries, sprains, or pain. No food was eaten 30 minutes before tests. Alcohol, tea, and coffee were prohibited on the test days. The participants practiced CPR on manikins before they began the tests. Effective chest compression was identified as chest compressions with a depth of more than or equal to 38 mm. Each participant subsequently performed continual external chest compressions at 2 compression rates on a Resusci Anne manikin (Laerdal Medical, Wappingers Falls, NY): 100-cpm (ie, continual external chest compressions without interrupting ventilations at a rate of 100 per min [100-cpm]) and the push-fast (PF) rate (ie, continual external chest compressions without interrupting ventilations at the asfast-as-you-can rate). The chest compression duration was 5 minutes for each session, alternating with interrupted rest periods of 50 minutes. The 5-minute chest compression involved a single nonprofessional rescuer performing occasionally for 5 minutes during a real cardiac arrest. This scenario was used in our previous study and in a study on the efficacy decay in CPR [13-15]. The order of the compression sessions was randomized.
From January to July 2010, 42 CPR-certified rescuers voluntarily participated in the study. Among them, 21 were women. The mean age of the rescuers was 24.8 ± 6.3 years, the mean height was 166.5 ± 7.5 cm, and the mean weight was 63.3 ± 13.6 kg. Table 1 shows chest compression data obtained from the Laerdal PC SkillReporting System for 5 minutes of external chest compressions. According to the power analysis for a paired t test, a sample size of 42 subjects had a reasonable power (1.00) to distinguish the 2 sessions of CPR based on compression rates. During the PF session, the rescuers performed CPR with higher compression rates, more compressions, more duty cycles, and a lower percentage of effective compressions and lower compression depths than they did during the 100-cpm session. We observed no differences in rescuer performance in incomplete release during the PF and 100cpm sessions.
2.3. Work while performing external cardiac compression Physical parameters, including heart rate, blood pressure, and oxygen saturation, were measured for each study participant before and after each CPR session. The measured variables were estimated maximum heart rate (EMHR = 220 − age) and heart rate as a percentage of EMHR at the end of each CPR. The visual analog scale (VAS) was used to rank the intensity of exercise across a continuum from 0 “none” to 10 “extreme exhaustion.” The participants rated how they felt before and after each CPR. After performing both sessions, they were asked “Which session is more exhausting: 100-cpm or PF?”
2.4. Performance of chest compression on the manikin Our experimental model consisted of a Laerdal Skillmeter ResusciAnne manikin located on the floor; performers kneeled beside the manikin's chest to mimic typical bystander resuscitations. The manikin was connected to a laptop computer, and external chest compression performance data were transmitted from the manikin to the computer. Data were collected using the Laerdal PC SkillReporting System (PC Skillmeter; Laerdal Medical, Stavanger, Norway). Data output from the Laerdal PC SkillReporting System included average compression rate, average compression depth, average duty cycle, total compressions counted, compressions registered with adequate depth, and compressions registered with incomplete release.
3.2. Rate of chest compressions Figure A shows the compression rate in the 100-cpm and PF sessions over the 5-minute period. The compression rates for each minute from the first to fifth minute were 158.1 ± 23.7, 152.3 ± 21.2, 154.7 ± 22.3, 158.3 ± 22.4, and 160.1 ± 23.6 per minute in the PF session and 99.0 ± 7.3, 101.0 ± 3.7, 102.0 ± 5.7, 103.2 ± 6.9, and 103.5 ± 7.6 per minute in the 100-cpm session. In subgroup analysis, we conducted analyses separately in female or male participants in the compression rates at each minute (Supplemental Figure A). The compression rate in the PF session was higher than that in the 100-cpm session. 3.3. Count of effective chest compressions Figure B shows the counts of chest compression with adequate depth. The counts of effective chest compressions for each minute from the first to fifth minute were 112.7 ± 58.8, 78.8 ± 68.2, 61.8 ± 69.2, 57.8 ± 70.3, and 56.1 ± 69.3 in the PF session and 78.0 ± 33.0, 65.1 ± 41.0, 54.7 ± 41.7, 49.1 ± 43.9, and 46.0 ± 44.1 in the 100-cpm session. The counts of effective chest compression deteriorated over time, and the deterioration was observed beginning in the third minute of the PF session and the fourth minute of the 100-cpm session. The counts of adequate compressions in the PF session were higher than those in the 100-cpm session were during the first minute. We observed no significant differences in the counts of adequate compression in the second to fifth minutes. We perform subgroup analyses separately for female or male participants in the counts of adequate compressions at each minute (Supplemental Figure B). The counts of effective chest compression deteriorated over time, and the deterioration was observed predominantly in the PF session in both genders.
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Table 1 Chest compression data during 5 minutes of CPR
Compression rate (per minute) Count of compressions/5 min Compression depth (mm) Percent of effective compressions (%) Count of effective compression/5 min Incomplete release (%) Duty cycle (%)
100-cpm
PF
101.6 ± 4.8 510.8 ± 24.2 38.0 ± 8.1 57.9 ± 36.4 292.9 ± 187.1 8.4 ± 24.8 41.7 ± 6.6
156.8 ± 21.7 787.2 ± 108.9 35.6 ± 12.4 47.7 ± 40.2 367.1 ± 310.3 6.9 ± 18.0 51.0 ± 5.6
Mean difference (95% CI) −55.2 (−62.1, −48.3)⁎⁎ −276.4 (−311.2, −241.7)⁎⁎ 2.4 (0.0, 4.8)⁎ 10.1 (2.3, 17.7)⁎ −74.2 (−137.7, −10.6)⁎ 1.5 (−3.8, 6.8) −9.2 (−11.5, -7.0)⁎⁎
Data were given as mean ± SD or mean difference (95% confidence interval). Abbreviation: CI, confidence interval. ⁎ P b .05. ⁎⁎ P b .001.
3.4. Percentile of effective chest compressions Figure C shows the percentile of effective chest compression between the 2 sessions. The percentile of effective compression for each minute from the first to fifth minute was 72.5 ± 36.5, 52.8 ± 44.9, 40.8 ± 45.6, 37.3 ± 45.4, and 36.1 ± 44.8 in the PF session and 77.5 ± 32.0, 64.6 ± 41.1, 54.4 ± 41.5, 48.5 ± 43.4, and 45.5 ± 43.5 in the 100-cpm session. The percentile of effective compressions deteriorated over time, showing an earlier percentile of effective chest compression
deterioration in the PF session than in the 100-cpm session (deterioration was noted from the third minute in the PF session vs the fourth minute in the 100-cpm session). The percentile of effective chest compression in the 100-cpm sessions was higher than that in the PF sessions during the second, third, and fourth minutes of CPR. We conducted subgroup analyses separately in female or male participants in the percentile of adequate compressions at each minute (Supplemental Figure C). The deteriorated percentile of effective chest compression was more predominant in the PF session than that in the 100-cpm session in both sexes. 3.5. Physiologic variables and perceived exertion Table 2 shows the physiologic variables and perceived exertion of rescuers measured after both sessions of CPR. We observed no difference in physiologic variables and VAS before the PF and 100-cpm sessions of CPR (data not shown). A comparison of physiological parameters after each session showed that the heart rate, estimated maximal heart rate, and VAS were significantly higher after rescuers finished the PF session than that after the 100-cpm session. No differences were evident in systolic blood pressure, mean arterial pressure, and oxygen saturation after 2 sessions of CPR. The questionnaire response revealed that chest compression at the PF rate was more exhausting than at the rate of 100 cpm for 38 participants (90.5%) and 100-cpm was more exhausting for 4 participants (9.5%). 4. Discussion 4.1. Summary of main findings The AHA recommends chest compression at the rate of as-fast-asyou-can, but the influence on CPR performance is unknown. We evaluated the effect of various compression rates of hands-only CPR, “push fast,” and 100-cpm on CPR quality and performer fatigue among nonprofessional rescuers. The features of the recommended PF technique were excessive compression rates more than 150 cpm and early deterioration in counts and percentile of effective compressions, compared with chest compression at a rate of 100 cpm. Rescuer fatigue was the Table 2 Physiologic variables and perceived exertion after external chest compressions
SBP (mm Hg) MAP (mm Hg) SpO2 (%) HR (per minute) %EMHR VAS Figure. The CPR performance of each minute was shown as mean, including count of chest compression (A), count of effective chest compression (B), and the percentile of effective chest compression (C). Data were given as mean. ⁎P b .05 compared to the CPR performance of100-cpm at indicated time; #P b .05 compared to the CPR performance of the first minute.
100-cpm
PF
125.4 ± 23.7 93.9 ± 14.9 96.9 ± 1.4 112.8 ± 23.3 57.7 ± 11.2 4.8 ± 2.1
129.2 ± 15.7 95.1 ± 12.9 97.0 ± 1.2 124.3 ± 20.8 63.6 ± 10.2 6.2 ± 2.1
Mean difference (95% CI) −3.8 (−10.3, 2.7) −1.2 (−4.9, 2.5) 0.0 (−0.5, 4.7) −11.5 (−18.8, −4.1)⁎ −5.9 (−9.7, −2.2)⁎ −1.5 (−2.1, −0.8)⁎⁎
Data were given as mean ± SD or mean difference (95% confidence interval). Abbreviations: SBP, systolic blood pressure; MAP, mean arterial pressure; SpO2, saturation O2; HR, hear rate; %EMHR, percentages of estimated maximum heart rate. ⁎ P b .01. ⁎⁎ P b .001.
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primary cause of deterioration in CPR efficacy, and the recommended PF technique showed a trend toward increased effort loading in the rescuers, compared with the 100-cpm rate. The optimal rate of chest compression remains unknown. According to the 2010 version of the AHA Guidelines for CPR, all rescuers should provide effective compressions at a rate of at least 100 pm without an upper rate limit [9]. However, the 2010 European Resuscitation Council CPR guidelines [10] recommend an upper rate limit of 120 cpm. Abella et al [5] showed a higher chest compression rate associated with a higher rate of return of spontaneous circulation. The mean chest compression rates for initial survivors were 90 ± 17 cpm and 79 ± 18 cpm for nonsurvivors. Idris et al [16] reported a relationship between chest compression rates and outcomes for cardiac arrest. The cubic spline curve for rate of return of spontaneous circulation peaked at a compression rate of 125 cpm and subsequently declined. Monsieurs et al [17] reported that excessive compression rates may lead to insufficient depth of compression. Consistent with the works of Idris et al and Monsieurs et al, our study revealed that the AHA guideline for the “asfast-as-you-can” compression rate resulted in an excessive compression rate of approximately 150 cpm and loss of compression depth. The recommended duty cycles ranging from 20% to 50% account for adequate coronary and cerebral perfusion [9]. Our results showed that the duty cycles in both rates of chest compression were within the recommended range. Previous studies have observed an increase in duty cycle at a faster rate and a duty cycle near 50% at a compression rate of 160 beats per minute [18,19]. Our results revealed an increased duty cycle reaching the recommended 50% during the PF session. Consistent with the study of Hightower et al [13], although the participants maintained an adequate rate in chest compression, CPR efficacy declined with time. According to the count or percentile of effective compressions in the study, the efficacy deterioration was noticeable within 3 minutes after starting CPR in the PF session and within 4 minutes in the 100-cpm session. The PF technique exhibited a trend toward in early decay of CPR quality. Previous studies have used a higher number of compressions, and the ventilation ratio exhibited an increased number of adequate chest compressions and attempted chest compressions [20,21]. We also observed an increased number of total and effective compressions performed in the PF session during the 5-minute CPR. The analysis of each minute of CPR performance revealed that the counts of effective compression were higher during the first minute in the PF session than in the 100-cpm session. However, the rescuers performed a higher percentile of effective chest compression in the 100-cpm session than in the PF session during the 5-minute CPR. The percentile of effective chest compression was higher in the 100-cpm session than in the PF session in the second to fourth minutes. Although the as-fast-as-you-can compression rate provided a higher compression count in the first minute of CPR, no difference was detected in the percentile of effective chest compression during the first minute of CPR. Compared with a chest compression rate of as-fast-as-you-can, the compression rate of 100 cpm for the 5-minute CPR is likely to maintain adequate chest compression quality in the percentile of effective compression and compression depth. Furthermore, in subgroup analysis for female or male participants, the decreased percentile of effective chest compression was more predominant in the PF session than in the 100-cpm sessions in both genders. Rottenberg [22-24] has reported that typical male rescuers were taller and have more upper-body weight than female rescuers and, therefore, are more physically capable of providing effective CPR. Chung et al [25] also showed that the compression depth was associated with rescuers' body weight, height, and sexes during metronome-guided CPR. In the present study, the decay in counts or percentile of effective chest compression was noted respectively in the second minute of CPR in female participants and in the third minute in male participants. Consistently, the decay in efficacy of CPR was noted earlier in female than in male participants. It may be considered to develop CPR recommendations as well as dispatcher-assisted CPR
instructions according to physical capacity of the rescuers. Further studies may be designed to determine separately for men and women the most appropriate compressions rate or depth that is likely to facilitate effective CPR performance. Rescuer fatigue during CPR can cause inadequate depth and rates of chest compression. To avoid a decline of CPR quality, the AHA recommends rotating rescuers every 2 minutes [9]. An evaluation of the heart rate and subjective scales of perceived exertion suggests that increasing consecutive compressions can increase exercise intensity and affect rescuer fatigue [12,26,27]. We demonstrated that using the PF recommendation resulted in a greater workload, measured by physiological variables and self-reporting perceived effort after 5 minutes of chest compression. Rotating rescuers every 2 minutes is, therefore, reasonable to increase effective compressions when promoting the PF protocol. 4.2. Limitations This study had certain limitations. First, the outcome measures excluded crucial clinical variables, including patient survival and physiology variables of resuscitation during the manikin studies. For example, gasping is essential for effective CPR and is associated with favorable survival and neurologic outcome [28–30]. The manikin study cannot reveal the effect of gasping on the rescuers' CPR performance and the survival or neurologic outcome of patients. Second, the study population included CPR trained nonprofessional rescuers. Although PF CPR targets untrained rescuers, CPR-trained rescuers were more likely to provide CPR than were people without CPR training [31]. Therefore, extrapolating this finding to the untrained public warrants caution. Finally, the AHA and the European Resuscitation Council 2010 guideline have recommended a push depth of at least 5 cm [10]. Chest compression quality deteriorated substantially over the study period in both protocols, suggesting that a depth above 5 cm might be challenging for rescuers to accomplish. 5. Conclusion The AHA recommends that rescuers perform CPR at the push-asfast-as-you-can rate, but the optimal rate is unknown. We evaluated the effect of hands-only CPR, PF, and 100-cpm techniques on CPR quality and performer fatigue among nonprofessional rescuers. Although the PF technique showed increasing numbers of compressions delivered each minute, we observed a significant decrease in the percentile of effective chest compressions compared with the 100-cpm technique during the 5-minute hands-only CPR. The PF technique exhibited a trend toward increased fatigue in the rescuers and can result in a deterioration tendency in the percentile of effective compression during CPR. Further studies are required to evaluate the effect of the PF recommendation for faster chest compressions. Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.ajem.2014.08.074. Acknowledgment The authors thank the National Science Council of the Republic of China, Taiwan (contract no. NSC 98-2320-B-006-001). We are also grateful to Shang-Chi Lee, MSc, for providing statistical consulting services from the Biostatistics Consulting Center, Research Center of Clinical Medicine, National Cheng Kung University Hospital. References [1] Travers AH, Rea TD, Bobrow BJ, Edelson DP, Berg RA, Sayre MR, et al. Part 4: CPR overview: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation 2010;122(18 Suppl 3): S676–84.
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