American Journal of Emergency Medicine 33 (2015) 535–538
Contents lists available at ScienceDirect
American Journal of Emergency Medicine journal homepage: www.elsevier.com/locate/ajem
Original Contribution
Rate at 120/min provides qualified chest compression during cardiopulmonary resuscitation☆,☆☆,★ Yaru Zou, MD a, Wen Shi, MD a, Ying Zhu, MD a, Ranjun Tao, MD a, Ying Jiang, MD b, Shanfeng Li, MD a, Jing Ye, PhD, MD a, Yiming Lu, PhD, MD a, Jie Jiang, MD a,⁎,1, Jianjing Tong, MD a,⁎,1 a b
Department of Emergency Medicine, Ruijin Hospital affiliated to Shanghai Jiaotong University, School of Medicine, Shanghai, China Ruijin Clinical Medical College, Ruijin Hospital affiliated to Shanghai Jiaotong University, School of Medicine, Shanghai, China
a r t i c l e
i n f o
Article history: Received 11 December 2014 Received in revised form 13 January 2015 Accepted 14 January 2015
a b s t r a c t Objectives: The quality of cardiopulmonary resuscitation (CPR) is a very important prognostic factor for cardiac arrest. Chest compression is thought to be one of the most important aspects of high-quality CPR. Recent studies have prompted that there may be an interaction between chest compression rate and other factors related to the quality of chest compression. We aimed to investigate the effect of different compression rates on chest compression depth, recoil, and rescuers' fatigue point during CPR. Methods: Participants performed 2 minutes of chest compression-only CPR after the guiding sounds, at 3 rates (100, 120, and 140 compressions/min) in random sequence. A repeated-measures analysis of variance was used to compare the average chest compression depth and other factors related to the quality of chest compression among the groups. Results: As the chest compression rate increases through all the 3 rates, the fractions of chest compressions with complete release and the fractions of chest compressions with sufficient depth were deteriorated at the rate of 140 compressions/min (P b .05), although the average compression depth was above the recommended 2010 guideline depth of 5 cm(P N .05). Of note, the fatigue point at 140 compressions/min happened significantly (P b .05) sooner. Conclusion: Our study supported the concern of some that there may be a risk of increasing recommended chest compression rate without providing an upper limit. An appropriate choice may be 120 compressions/min. © 2015 Elsevier Inc. All rights reserved.
1. Introduction With the increase of the incidence of coronary heart disease, the incidence of sudden cardiac arrest (SCA) also increases. Cardiopulmonary resuscitation (CPR) after SCA is known to reduce mortality and leads to approximately a 3-fold increase in post-SCA discharge from hospitals, potentially negating its significant health care burden [1]. The quality of prehospital resuscitation is important to achieve return of spontaneous circulation (ROSC) [2]. In an effort to improve SCA outcomes, recent investigations have focused on the quality of CPR [3,4]. Previous studies have shown that higher chest compression rates were significantly correlated with initial ROSC [5]. Although CPR is traditionally composed of chest compressions accompanied by ventilations, recent work suggests that increasing the
☆ Equipments: Resusci Anne QCPR manikin (Laerdal, Stavanger, Norway). ☆☆ Grants: Shanghai Science and Technology Committee (no. 11ZR1422100). ★ Conflict of interest: The authors indicate no potential conflicts of interest. ⁎ Corresponding authors. Department of Emergency Medicine, Ruijin Hospital affiliated to Shanghai Jiaotong University, School of Medicine, No. 197 Ruijin Er Road, Huangpu District, Shanghai, China. E-mail addresses: [email protected] (J. Jiang), [email protected] (J. Tong). 1 The authors contributed equally to the work, both are corresponding authors. http://dx.doi.org/10.1016/j.ajem.2015.01.024 0735-6757/© 2015 Elsevier Inc. All rights reserved.
ratio of chest compressions to ventilations may improve the probability of the ROSC [6]. Moreover, chest compression-only CPR becomes more attractive recently because it is simpler to perform and also delivers a greater number of chest compressions than conventional CPR [7]. Chest compression-only CPR has been encouraged by the American Heart Association (AHA) to serve as an alternative to conventional CPR for untrained bystanders or trained bystanders who are not able to perform rescue breathing [8]. High-quality CPR recommended in the AHA and European Resuscitation Council (ERC) 2010 guidelines for basic life support (BLS) consists of the following: provide chest compressions at an adequate rate (≥100/min), provide chest compressions at an adequate depth (a compression depth of ≥2 in or 5 cm for adult), allow complete chest recoil after each compression, minimize interruptions between compressions, and avoid excessive ventilation. It is thought provoking that the AHA and ERC 2010 guidelines for BLS both advise rescuers to push harder and faster [4,8]. However, this may increase physical exertion and fatigue for rescuers [9]. Furthermore, other factors related to the quality of chest compression may change due to fatigue. Recent studies have prompted that there may be an interaction between chest compression rate and other factors related to the quality of chest compression [10]. We aimed to investigate the effect of different compression rates on average chest compression depth, recoil, and the rescuers' fatigue
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Y. Zou et al. / American Journal of Emergency Medicine 33 (2015) 535–538
point during CPR. This study is helpful to find the appropriate chest compression rate for obtaining a high-quality CPR method. 2. Materials and methods
and a Wilcoxon signed rank test were used for nonparametric data. The normally distributed data were presented as the mean or percentage with SD. The results of the statistical tests were considered significant when the P value was b .05. A sample size of 24 was required to detect a 10% difference in the ACDs for each trial at a power of 0.90.
2.1. Study design 3. Results This was a prospective, crossover study of simulated, 1-person, chest compression-only CPR. Three different methods of compression-only CPR based on 3 different rates were performed. The aim was to investigate the effect of different compression rates on average chest compression depth, recoil, and the rescuers' fatigue point under the latest 2010 AHA CPR guidelines. The study protocol was approved by the Institutional Review Board of Shanghai Ruijin Hospital. 2.2. Participants Study subjects were recruited from the emergency department personnel. The whole crew performing CPR was certified in AHA BLS. Participants, whose certification expired, who had a history of significant medical illnesses, or who could not tolerate hard exercise, were excluded. All participants received written information about the study and consented to participate. 2.3. Equipment A Resusci Anne QCPR manikin equipped with a PC Skillreporting system (Laerdal, Stavanger, Norway) was used for measuring and recording CPR data. The monitoring screen was not visible for the participants, and no feedback was given. The manikin was placed on the ground for standardization. Metronome sounds were synthesized using the audiosynthesizing software Reason (Propellerhead, Stockholm, Sweden). Three different metronome rates were used: 100, 120, and 140 ticks/min. 2.4. Study protocols Three sets of chest compression-only CPR for 2 minutes were performed after the metronome sounds, which were played with rates of 100, 120, and 140 compressions/min in a random sequence. The data on CPR performance were automatically collected by the software. No feedback was provided to the participants during the entire CPR procedure. To avoid the effect of rescuer fatigue, sufficient rest time was allowed between the trials (N30 min). The study protocol was approved by the Institutional Review Board of Shanghai Ruijin Hospital. 2.5. Data collection For each set, the total number of chest compressions, average compression depth (ACD), the fractions of chest compressions with complete release, the fractions of chest compressions with sufficient depth, and correct hand position were recorded. To evaluate the fatigue parameter, the time at which 5 consecutive compression depths could not achieve the standard was defined as the fatigue point. In addition, demographic information of every participant was also recorded, including age, sex, height, weight, and calculated body mass index (BMI). Data collection procedures were completed to comply with the guidelines of the Health Insurance Portability and Accountability Act to ensure subject confidentiality.
3.1. Baseline characteristics of participants There were no significant differences in the baseline characteristics of the participants, including demographic data such as age, sex, height, weight, and calculated BMI (Table). Furthermore, there were no significant differences in every measurable parameter, including the total number of chest compressions, ACD, the fractions of chest compressions with complete release, the fractions of chest compressions with sufficient depth, and correct hand position, classified by age, sex, and BMI, respectively (P N .05). 3.2. Quality analysis of chest compressions 3.2.1. Total number of chest compressions As the chest compression rate increased, the total number of compressions delivered within the 2-minute trial increased significantly. The data showed an average of 204, 251, and 287 compressions delivered at the chest compression rates of 100, 120, and 140 compressions/min, respectively (P b .0001). 3.2.2. Average compression depth For all the 3 rates, the ACD was above the recommended 2010 guideline depth of 5 cm. There were no significant differences (P = .8526) in the 3 rates or any 2 of them (Fig. 1). 3.2.3. The fractions of chest compressions with complete release The fractions of chest compressions with complete release at the chest compression rates of 100, 120, and 140 compressions/min were 80.7037%, 89.0741%, and 70.0370%, respectively. Among them, the difference between 120 and 140 compressions/min was significant (P b .05) (Fig. 2). 3.2.4. The fractions of chest compressions with sufficient depth As the chest compression rate increased, what we should observe was the poor fractions of chest compressions with sufficient depth at the rate of 100 and 140 compressions/min. Interestingly, the highest percentage occurred at the middle rate. In addition, the fractions of chest compressions with sufficient depth at the rate of 120 were significantly different from that of 100 or 140 compressions/min (Fig. 3). 3.2.5. Correct hand position As the chest compression rate increased, there was an increased percentage of correct hand position. The percentages of correct hand position are 59.0556%, 91.1579%, and 100% at the chest compression rates of 100, 120, and 140 compressions/min, respectively. However, the difference between 100 and 120 compressions/min was significant (P b .05), whereas the difference between 120 and 140 was not (Fig. 4).
Table Demographic information of the participants
2.6. Statistical analysis All data were analyzed using a SAS statistical software package for Windows, version 8.0 (Cary, NC). A repeated-measures analysis of variance was used to compare the quality of chest compression for the CPR procedures after the different metronome rates. A Friedman test
n (%) Age (y) Sex Male Female BMI
27 11 (41%) 16 (59%) 27
Mean ± SD 32 ± 6.86
22.18 ± 2.82
Y. Zou et al. / American Journal of Emergency Medicine 33 (2015) 535–538
Fig. 1. Average compression depth of the trials with different rate of chest compressions according to the rate of metronome. Bars represent mean ± SD.
3.2.6. Fatigue point Fatigue point in our study was defined as the time at which 5 consecutive compression depths could not achieve the standard. Fatigue occurred at 96, 106, and 78 seconds for rates of 100, 120, and 140 compressions/min, respectively. It is worth mentioning that the difference between 120 and 140 compressions/min was significant (P b .05) as well as that between 100 and 140 compressions/min (Fig. 5). 4. Discussion In 2010 guidelines, there was a dramatic shift from a sequence that emphasized airway management first Airway-Breathing-Circulation (A-B-C) to one that focused on providing early high-quality chest compressions Circulation-Airway-Breathing (C-A-B) [8]. It is not hard to see that the quality of chest compression is closely associated with CA outcome compared with ventilations. As described in the previous section, the quality of chest compressions requirements was significantly improved after the 2010 AHA guidelines. However, it is more difficult for the rescuers to meet the requirements of the guidelines due to the potential factors of increased physical exertion and rescuer fatigue [10]. To direct CPR training and practice better, an upper limit of the recommended chest compression rate should be provided. 4.1. Summary of main findings Our study demonstrated that, during 2 minutes of compression-only CPR, all of the 3 groups could achieve the target ACD (5 cm) according to 2010 guidelines. However, when the rate got to 140 compressions/min, the chest compression quality (in terms of the fractions of chest compressions with complete release and the fractions of chest compressions with sufficient depth and fatigue point) was deteriorated. To our surprise, when the rate fell to 100 compressions/min, the fractions of chest compressions with sufficient depth and the fractions of correct hand position were not satisfactory as well.
Fig. 2. The fractions of chest compressions with complete release of the trials with different rate of chest compressions according to the rate of metronome. Bars represent mean ± SD. ⁎P b .05.
537
Fig. 3. The fractions of chest compressions with sufficient depth of the trials with different rate of chest compressions according to the rate of metronome. Bars represent mean ± SD. ⁎P b .05.
4.1.1. One hundred forty compressions/min might lead to fatigue point occurred early and sternum imcomplete rebounded In our study, the chest compression rate was not an entire mutually exclusive variable to other chest compression quality factors. The main advantage of increasing compression rate (140 compressions/min) was a significant increase in the fractions of correct hand position, which was close to 100%. However, this might be at the cost of the incomplete rebounded sternum (rescuers' hands never left the chest wall). The main drawbacks of excessively fast compression rates were a significant decrease in the time at which fatigue occurred, the decay of compression quality, and a significant decrease in adequate compression depth. 4.1.2. One hundred compressions/min should pay attention to hand position In this study, we have observed that, at the rate of 100 compressions/ min, the fractions of chest compressions with sufficient depth decreased significantly, and the fractions of correct hand position were very poor. We cannot definitely explain why this rate cannot improve chest compression quality in our study, but we can offer a speculation. In the present study, we acquired a metronome to control the rate. When the metronome guidance was used, the chest compression rate was within the current guidelines, but the number of actually performed chest compressions per minute was lower, compared with other rates. In the other words, the pause between the consecutive compressions was longer at this rate. According to our experience, our hands were more likely left chest wall during the longer pause. Consequently, the fractions of correct hand position were small. According to the physical knowledge, if we want to acquire higher speed, we need give out greater strength. It is not hard to figure that the power is insufficient at the lower rate. Therefore, it is difficult to achieve the sufficient depth. Moreover, previous studies have shown that using a metronome or
Fig. 4. The percentage of correct hand position of the trials with different rate of chest compressions according to the rate of metronome. Bars represent mean ± SD. ⁎P b .05.
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to the metronome-guided CPR because there could have been an additional effect of metronome guidance on the quality of chest compression. Further studies concentrating on this area are needed. 5. Conclusion Our study supported the concern of some people that there may be a risk of increasing recommended chest compression rate without providing an upper limit. Based on our study, we recommended 120 compressions/min as an appropriate choice. Further study is necessary to validate the recommended chest compression rate for establishing the renewed guidelines. Acknowledgments Fig. 5. Fatigue point of the trials with different rate of chest compressions according to the rate of metronome. Bars represent mean ± SD. ⁎P b .05.
music to guide compression rates might lead to a slight decrease in depth, compared with no metronome or music [11,12]. It could also be one of the reasons. 4.1.3. One hundred twenty compressions/min could acquire better CPR quality We found that, in this study, the rate of 120 compressions/min seemed considerable. At the rate of 120 compressions/min, rescuers could achieve the target ACD and keep it sufficient most of the time (~90%), which was the vital factor to ROSC. The recoil was approximate to 90%, which was more sufficient than that of 140 compressions/min. At the same time, the wrong hand placement was nearly not observed. Above all, using 120 compressions/min, the arrival of our fatigue comes later (106 seconds) than the other 2 rates. Both the AHA and ERC guidelines have recommended changing the rescuer every 2 minutes (120 seconds) to prevent a serious decline in the quality of chest compressions resulted from rescuer fatigue [4,8]. Combined with 120 compressions/min, they brought out the best in each other. Interestingly, in a recent 2012 out-of-hospital adult CA investigation, the Resuscitation Outcomes Consortium demonstrated that ROSC peaked at a compression rate of approximately 125/min and then declined [13]. This result provided evidence for our hypothesis. 4.2. Limitations Our study has a few limitations. First, this was a manikin-based simulation study, which is quite different from the clinical setting. It is not clear whether the quality of CPR given to manikins is equivalent to the quality of CPR given to patients. Subsequently, direct implementation of our findings in a clinical setting should be performed with great caution. Second, every chest compression in the study was performed with metronome guiding because of the need to induce a certain chest compression rate range. Therefore, an application of the results is limited
The authors thank Kerui Liu at Ohio State University for her involvement in the article-revising process. We would like to thank all participating BLS health care providers who contributed to this study. References [1] Sasson C, Rogers MA, Dahl J, Kellermann AL. Predictors of survival from out-ofhospital cardiac arrest: a systematic review and meta-analysis. Circ Cardiovasc Qual Outcomes 2010;3(1):63–81. [2] Lee SH, Kim K, Lee JH, Kim T, Kang C, Park C, et al. Does the quality of chest compressions deteriorate when the chest compression rate is above 120/min? Emerg Med J 2014;31(8):645–8. [3] Edelson DP, Abella BS, Kramer-Johansen J, Wik L, Myklebust H, Barry AM, et al. Effects of compression depth and pre-shock pauses predict defibrillation failure during cardiac arrest. Resuscitation 2006;71(2):137–45. [4] Nolan JP, Soar J, Zideman DA, Biarent D, Bossaert LL, Deakin C, et al. European Resuscitation Council Guidelines for Resuscitation 2010 Section 1. Executive summary. Resuscitation 2010;81(10):1219–76. [5] Abella BS, Sandbo N, Vassilatos P, Alvarado JP, O'Hearn N, Wigder HN, et al. Chest compression rates during cardiopulmonary resuscitation are suboptimal: a prospective study during in-hospital cardiac arrest. Circulation 2005;111(4): 428–34. [6] Sanders AB, Kern KB, Berg RA, Hilwig RW, Heidenrich J, Ewy GA. Survival and neurologic outcome after cardiopulmonary resuscitation with four different chest compression-ventilation ratios. Ann Emerg Med 2002;40(6):553–62. [7] Heidenreich JW, Sanders AB, Higdon TA, Kern KB, Berg RA, Ewy GA. Uninterrupted chest compression CPR is easier to perform and remember than standard CPR. Resuscitation 2004;63(2):123–30. [8] Berg RA, Hemphill R, Abella BS, Aufderheide TP, Cave DM, Hazinski MF, et al. Part 5: adult basic life support: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation 2010; 122(18 Suppl 3):S685–705. [9] McDonald CH, Heggie J, Jones CM, Thorne CJ, Hulme J. Rescuer fatigue under the 2010 ERC guidelines, and its effect on cardiopulmonary resuscitation (CPR) performance. Emerg Med J 2013;30(8):623–7. [10] Yang Z, Li H, Yu T, Chen C, Xu J, Chu Y, et al. Quality of chest compressions during compression-only CPR: a comparative analysis following the 2005 and 2010 American Heart Association guidelines. Am J Emerg Med 2014;32(1):50–4. [11] Jantti H, Silfvast T, Turpeinen A, Kiviniemi V, Uusaro A. Influence of chest compression rate guidance on the quality of cardiopulmonary resuscitation performed on manikins. Resuscitation 2009;80(4):453–7. [12] Rawlins L, Woollard M, Williams J, Hallam P. Effect of listening to Nellie the Elephant during CPR training on performance of chest compressions by lay people: randomised crossover trial. BMJ 2009;339(2) [b4707-b]. [13] Idris AH, Guffey D, Aufderheide TP, Brown S, Morrison LJ, Nichols P, et al. Relationship between chest compression rates and outcomes from cardiac arrest. Circulation 2012;125(24):3004–12.
Contents lists available at ScienceDirect
American Journal of Emergency Medicine journal homepage: www.elsevier.com/locate/ajem
Original Contribution
Rate at 120/min provides qualified chest compression during cardiopulmonary resuscitation☆,☆☆,★ Yaru Zou, MD a, Wen Shi, MD a, Ying Zhu, MD a, Ranjun Tao, MD a, Ying Jiang, MD b, Shanfeng Li, MD a, Jing Ye, PhD, MD a, Yiming Lu, PhD, MD a, Jie Jiang, MD a,⁎,1, Jianjing Tong, MD a,⁎,1 a b
Department of Emergency Medicine, Ruijin Hospital affiliated to Shanghai Jiaotong University, School of Medicine, Shanghai, China Ruijin Clinical Medical College, Ruijin Hospital affiliated to Shanghai Jiaotong University, School of Medicine, Shanghai, China
a r t i c l e
i n f o
Article history: Received 11 December 2014 Received in revised form 13 January 2015 Accepted 14 January 2015
a b s t r a c t Objectives: The quality of cardiopulmonary resuscitation (CPR) is a very important prognostic factor for cardiac arrest. Chest compression is thought to be one of the most important aspects of high-quality CPR. Recent studies have prompted that there may be an interaction between chest compression rate and other factors related to the quality of chest compression. We aimed to investigate the effect of different compression rates on chest compression depth, recoil, and rescuers' fatigue point during CPR. Methods: Participants performed 2 minutes of chest compression-only CPR after the guiding sounds, at 3 rates (100, 120, and 140 compressions/min) in random sequence. A repeated-measures analysis of variance was used to compare the average chest compression depth and other factors related to the quality of chest compression among the groups. Results: As the chest compression rate increases through all the 3 rates, the fractions of chest compressions with complete release and the fractions of chest compressions with sufficient depth were deteriorated at the rate of 140 compressions/min (P b .05), although the average compression depth was above the recommended 2010 guideline depth of 5 cm(P N .05). Of note, the fatigue point at 140 compressions/min happened significantly (P b .05) sooner. Conclusion: Our study supported the concern of some that there may be a risk of increasing recommended chest compression rate without providing an upper limit. An appropriate choice may be 120 compressions/min. © 2015 Elsevier Inc. All rights reserved.
1. Introduction With the increase of the incidence of coronary heart disease, the incidence of sudden cardiac arrest (SCA) also increases. Cardiopulmonary resuscitation (CPR) after SCA is known to reduce mortality and leads to approximately a 3-fold increase in post-SCA discharge from hospitals, potentially negating its significant health care burden [1]. The quality of prehospital resuscitation is important to achieve return of spontaneous circulation (ROSC) [2]. In an effort to improve SCA outcomes, recent investigations have focused on the quality of CPR [3,4]. Previous studies have shown that higher chest compression rates were significantly correlated with initial ROSC [5]. Although CPR is traditionally composed of chest compressions accompanied by ventilations, recent work suggests that increasing the
☆ Equipments: Resusci Anne QCPR manikin (Laerdal, Stavanger, Norway). ☆☆ Grants: Shanghai Science and Technology Committee (no. 11ZR1422100). ★ Conflict of interest: The authors indicate no potential conflicts of interest. ⁎ Corresponding authors. Department of Emergency Medicine, Ruijin Hospital affiliated to Shanghai Jiaotong University, School of Medicine, No. 197 Ruijin Er Road, Huangpu District, Shanghai, China. E-mail addresses: [email protected] (J. Jiang), [email protected] (J. Tong). 1 The authors contributed equally to the work, both are corresponding authors. http://dx.doi.org/10.1016/j.ajem.2015.01.024 0735-6757/© 2015 Elsevier Inc. All rights reserved.
ratio of chest compressions to ventilations may improve the probability of the ROSC [6]. Moreover, chest compression-only CPR becomes more attractive recently because it is simpler to perform and also delivers a greater number of chest compressions than conventional CPR [7]. Chest compression-only CPR has been encouraged by the American Heart Association (AHA) to serve as an alternative to conventional CPR for untrained bystanders or trained bystanders who are not able to perform rescue breathing [8]. High-quality CPR recommended in the AHA and European Resuscitation Council (ERC) 2010 guidelines for basic life support (BLS) consists of the following: provide chest compressions at an adequate rate (≥100/min), provide chest compressions at an adequate depth (a compression depth of ≥2 in or 5 cm for adult), allow complete chest recoil after each compression, minimize interruptions between compressions, and avoid excessive ventilation. It is thought provoking that the AHA and ERC 2010 guidelines for BLS both advise rescuers to push harder and faster [4,8]. However, this may increase physical exertion and fatigue for rescuers [9]. Furthermore, other factors related to the quality of chest compression may change due to fatigue. Recent studies have prompted that there may be an interaction between chest compression rate and other factors related to the quality of chest compression [10]. We aimed to investigate the effect of different compression rates on average chest compression depth, recoil, and the rescuers' fatigue
536
Y. Zou et al. / American Journal of Emergency Medicine 33 (2015) 535–538
point during CPR. This study is helpful to find the appropriate chest compression rate for obtaining a high-quality CPR method. 2. Materials and methods
and a Wilcoxon signed rank test were used for nonparametric data. The normally distributed data were presented as the mean or percentage with SD. The results of the statistical tests were considered significant when the P value was b .05. A sample size of 24 was required to detect a 10% difference in the ACDs for each trial at a power of 0.90.
2.1. Study design 3. Results This was a prospective, crossover study of simulated, 1-person, chest compression-only CPR. Three different methods of compression-only CPR based on 3 different rates were performed. The aim was to investigate the effect of different compression rates on average chest compression depth, recoil, and the rescuers' fatigue point under the latest 2010 AHA CPR guidelines. The study protocol was approved by the Institutional Review Board of Shanghai Ruijin Hospital. 2.2. Participants Study subjects were recruited from the emergency department personnel. The whole crew performing CPR was certified in AHA BLS. Participants, whose certification expired, who had a history of significant medical illnesses, or who could not tolerate hard exercise, were excluded. All participants received written information about the study and consented to participate. 2.3. Equipment A Resusci Anne QCPR manikin equipped with a PC Skillreporting system (Laerdal, Stavanger, Norway) was used for measuring and recording CPR data. The monitoring screen was not visible for the participants, and no feedback was given. The manikin was placed on the ground for standardization. Metronome sounds were synthesized using the audiosynthesizing software Reason (Propellerhead, Stockholm, Sweden). Three different metronome rates were used: 100, 120, and 140 ticks/min. 2.4. Study protocols Three sets of chest compression-only CPR for 2 minutes were performed after the metronome sounds, which were played with rates of 100, 120, and 140 compressions/min in a random sequence. The data on CPR performance were automatically collected by the software. No feedback was provided to the participants during the entire CPR procedure. To avoid the effect of rescuer fatigue, sufficient rest time was allowed between the trials (N30 min). The study protocol was approved by the Institutional Review Board of Shanghai Ruijin Hospital. 2.5. Data collection For each set, the total number of chest compressions, average compression depth (ACD), the fractions of chest compressions with complete release, the fractions of chest compressions with sufficient depth, and correct hand position were recorded. To evaluate the fatigue parameter, the time at which 5 consecutive compression depths could not achieve the standard was defined as the fatigue point. In addition, demographic information of every participant was also recorded, including age, sex, height, weight, and calculated body mass index (BMI). Data collection procedures were completed to comply with the guidelines of the Health Insurance Portability and Accountability Act to ensure subject confidentiality.
3.1. Baseline characteristics of participants There were no significant differences in the baseline characteristics of the participants, including demographic data such as age, sex, height, weight, and calculated BMI (Table). Furthermore, there were no significant differences in every measurable parameter, including the total number of chest compressions, ACD, the fractions of chest compressions with complete release, the fractions of chest compressions with sufficient depth, and correct hand position, classified by age, sex, and BMI, respectively (P N .05). 3.2. Quality analysis of chest compressions 3.2.1. Total number of chest compressions As the chest compression rate increased, the total number of compressions delivered within the 2-minute trial increased significantly. The data showed an average of 204, 251, and 287 compressions delivered at the chest compression rates of 100, 120, and 140 compressions/min, respectively (P b .0001). 3.2.2. Average compression depth For all the 3 rates, the ACD was above the recommended 2010 guideline depth of 5 cm. There were no significant differences (P = .8526) in the 3 rates or any 2 of them (Fig. 1). 3.2.3. The fractions of chest compressions with complete release The fractions of chest compressions with complete release at the chest compression rates of 100, 120, and 140 compressions/min were 80.7037%, 89.0741%, and 70.0370%, respectively. Among them, the difference between 120 and 140 compressions/min was significant (P b .05) (Fig. 2). 3.2.4. The fractions of chest compressions with sufficient depth As the chest compression rate increased, what we should observe was the poor fractions of chest compressions with sufficient depth at the rate of 100 and 140 compressions/min. Interestingly, the highest percentage occurred at the middle rate. In addition, the fractions of chest compressions with sufficient depth at the rate of 120 were significantly different from that of 100 or 140 compressions/min (Fig. 3). 3.2.5. Correct hand position As the chest compression rate increased, there was an increased percentage of correct hand position. The percentages of correct hand position are 59.0556%, 91.1579%, and 100% at the chest compression rates of 100, 120, and 140 compressions/min, respectively. However, the difference between 100 and 120 compressions/min was significant (P b .05), whereas the difference between 120 and 140 was not (Fig. 4).
Table Demographic information of the participants
2.6. Statistical analysis All data were analyzed using a SAS statistical software package for Windows, version 8.0 (Cary, NC). A repeated-measures analysis of variance was used to compare the quality of chest compression for the CPR procedures after the different metronome rates. A Friedman test
n (%) Age (y) Sex Male Female BMI
27 11 (41%) 16 (59%) 27
Mean ± SD 32 ± 6.86
22.18 ± 2.82
Y. Zou et al. / American Journal of Emergency Medicine 33 (2015) 535–538
Fig. 1. Average compression depth of the trials with different rate of chest compressions according to the rate of metronome. Bars represent mean ± SD.
3.2.6. Fatigue point Fatigue point in our study was defined as the time at which 5 consecutive compression depths could not achieve the standard. Fatigue occurred at 96, 106, and 78 seconds for rates of 100, 120, and 140 compressions/min, respectively. It is worth mentioning that the difference between 120 and 140 compressions/min was significant (P b .05) as well as that between 100 and 140 compressions/min (Fig. 5). 4. Discussion In 2010 guidelines, there was a dramatic shift from a sequence that emphasized airway management first Airway-Breathing-Circulation (A-B-C) to one that focused on providing early high-quality chest compressions Circulation-Airway-Breathing (C-A-B) [8]. It is not hard to see that the quality of chest compression is closely associated with CA outcome compared with ventilations. As described in the previous section, the quality of chest compressions requirements was significantly improved after the 2010 AHA guidelines. However, it is more difficult for the rescuers to meet the requirements of the guidelines due to the potential factors of increased physical exertion and rescuer fatigue [10]. To direct CPR training and practice better, an upper limit of the recommended chest compression rate should be provided. 4.1. Summary of main findings Our study demonstrated that, during 2 minutes of compression-only CPR, all of the 3 groups could achieve the target ACD (5 cm) according to 2010 guidelines. However, when the rate got to 140 compressions/min, the chest compression quality (in terms of the fractions of chest compressions with complete release and the fractions of chest compressions with sufficient depth and fatigue point) was deteriorated. To our surprise, when the rate fell to 100 compressions/min, the fractions of chest compressions with sufficient depth and the fractions of correct hand position were not satisfactory as well.
Fig. 2. The fractions of chest compressions with complete release of the trials with different rate of chest compressions according to the rate of metronome. Bars represent mean ± SD. ⁎P b .05.
537
Fig. 3. The fractions of chest compressions with sufficient depth of the trials with different rate of chest compressions according to the rate of metronome. Bars represent mean ± SD. ⁎P b .05.
4.1.1. One hundred forty compressions/min might lead to fatigue point occurred early and sternum imcomplete rebounded In our study, the chest compression rate was not an entire mutually exclusive variable to other chest compression quality factors. The main advantage of increasing compression rate (140 compressions/min) was a significant increase in the fractions of correct hand position, which was close to 100%. However, this might be at the cost of the incomplete rebounded sternum (rescuers' hands never left the chest wall). The main drawbacks of excessively fast compression rates were a significant decrease in the time at which fatigue occurred, the decay of compression quality, and a significant decrease in adequate compression depth. 4.1.2. One hundred compressions/min should pay attention to hand position In this study, we have observed that, at the rate of 100 compressions/ min, the fractions of chest compressions with sufficient depth decreased significantly, and the fractions of correct hand position were very poor. We cannot definitely explain why this rate cannot improve chest compression quality in our study, but we can offer a speculation. In the present study, we acquired a metronome to control the rate. When the metronome guidance was used, the chest compression rate was within the current guidelines, but the number of actually performed chest compressions per minute was lower, compared with other rates. In the other words, the pause between the consecutive compressions was longer at this rate. According to our experience, our hands were more likely left chest wall during the longer pause. Consequently, the fractions of correct hand position were small. According to the physical knowledge, if we want to acquire higher speed, we need give out greater strength. It is not hard to figure that the power is insufficient at the lower rate. Therefore, it is difficult to achieve the sufficient depth. Moreover, previous studies have shown that using a metronome or
Fig. 4. The percentage of correct hand position of the trials with different rate of chest compressions according to the rate of metronome. Bars represent mean ± SD. ⁎P b .05.
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to the metronome-guided CPR because there could have been an additional effect of metronome guidance on the quality of chest compression. Further studies concentrating on this area are needed. 5. Conclusion Our study supported the concern of some people that there may be a risk of increasing recommended chest compression rate without providing an upper limit. Based on our study, we recommended 120 compressions/min as an appropriate choice. Further study is necessary to validate the recommended chest compression rate for establishing the renewed guidelines. Acknowledgments Fig. 5. Fatigue point of the trials with different rate of chest compressions according to the rate of metronome. Bars represent mean ± SD. ⁎P b .05.
music to guide compression rates might lead to a slight decrease in depth, compared with no metronome or music [11,12]. It could also be one of the reasons. 4.1.3. One hundred twenty compressions/min could acquire better CPR quality We found that, in this study, the rate of 120 compressions/min seemed considerable. At the rate of 120 compressions/min, rescuers could achieve the target ACD and keep it sufficient most of the time (~90%), which was the vital factor to ROSC. The recoil was approximate to 90%, which was more sufficient than that of 140 compressions/min. At the same time, the wrong hand placement was nearly not observed. Above all, using 120 compressions/min, the arrival of our fatigue comes later (106 seconds) than the other 2 rates. Both the AHA and ERC guidelines have recommended changing the rescuer every 2 minutes (120 seconds) to prevent a serious decline in the quality of chest compressions resulted from rescuer fatigue [4,8]. Combined with 120 compressions/min, they brought out the best in each other. Interestingly, in a recent 2012 out-of-hospital adult CA investigation, the Resuscitation Outcomes Consortium demonstrated that ROSC peaked at a compression rate of approximately 125/min and then declined [13]. This result provided evidence for our hypothesis. 4.2. Limitations Our study has a few limitations. First, this was a manikin-based simulation study, which is quite different from the clinical setting. It is not clear whether the quality of CPR given to manikins is equivalent to the quality of CPR given to patients. Subsequently, direct implementation of our findings in a clinical setting should be performed with great caution. Second, every chest compression in the study was performed with metronome guiding because of the need to induce a certain chest compression rate range. Therefore, an application of the results is limited
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