Introduction

Chest compressions (CCs) play a vital role in successful cardiopulmonary resuscitation (CPR)[1]. According to American Heart Association (AHA) 2015 guideline, high quality of CCs demand several conditions; Hand position should be two hands on the lower half of the sternum, chest compression should be performed at a rate of 100-120/min, full recoil of chest should be performed after each compression and minimizing interruptions[1]. CCs with an adequate depth has been recognized as an important aspect of high-quality CPR for survival and for favorable neurological outcomes[2]. Compression depth has been changed to at least 5 cm but should not exceed 6 cm in 2015 AHA recommendations from at least 5 cm in 2010[1]. The definition of appropriate rate of CCs was also changed to 100-120/min in 2015 from at least 100/min in 2010. In recent observational study, increased median duration of resuscitation, longest 25-mins, had a higher likelihood of return of spontaneous circulation during in-hospital cardiac arrest.[3] This study suggested the longer duration of CPR could improve survival rate in–hospital cardiac arrest, however, to maintain correct compressions with sufficient depth is considerably difficult throughout the course of long CPR. [4, 5] Many previous studies have proven that rescuer fatigue negatively affects CC depth especially during the longer CPR.[4, 6, 7] Although AHA recommends to change chest compression person in every 2 min cycle to maintain high quality CPR, to our knowledge, no previous study has illustrated the sufficient number of personnel in total required to perform CCs taking into account minimal rescuer fatigue in 30 min CPR. The aim of our study was to ascertain the sufficient number of personnel needed for CCs with adequate depth during 30 min CPR.

Materials and methods

Results and discussion

Participants’ characteristics

During the study period, we recruited 143 participants (median age 23 years, male 58(40%)). Two participants in group A dropped from this trial because they got too tired to continue CC. Therefore this study involved 141 participants for the analyses. This was more than pre-defined number of participants and therefore we think this study has enough power. We randomly assigned them to one of the four groups. The flow chart was shown in Fig 1. The baseline characteristics of the participants are shown in Table 1. No statistically significant differences in body weight, height, sex, and previous CPR training were observed among the participants of the four groups.

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Fig 1. Participant flow chart.

https://doi.org/10.1371/journal.pone.0189412.g001

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Table 1. Participants’ characteristics.

https://doi.org/10.1371/journal.pone.0189412.t001

Decline in the quality of CCs depending on decreasing CC personnel.

The results of the sufficient CC depth ratio, CC quickness and sufficient recoil ratio of each group in each cycle are shown in Table 2. Even though it was not statistically significant, the median of sufficient CC depth ratio in group A and B gradually decreased over 30 min course as compared to group C and D. In all four groups, CC quickness increased each cycles and recoil rate remained stable overall.

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Table 2. Sufficient CC depth ratio, CC quickness and complete recoil rate in each cycle over 30 min CPR.

https://doi.org/10.1371/journal.pone.0189412.t002

The main results of our study are shown in Table 3. With the decrease in the CC rest period, a significant decrease in the sufficient CC depth ratio was observed in the second to the last cycle as compared to the first cycle. The median changes were −4%, −3%, 0%, and 0% in groups A, B, C, and D, respectively; the differences were statistically significant (p < 0.01). The decrease was profound for female participants (−13%, −6% 0%, and 0%; p = 0.03). Alternatively, we did not find significant changes for the male participants (0%, 0%, 0%, and 0%; p = 0.4).

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Table 3. Differences of the outcomes between 1st chest compression cycle and 2nd to the last chest compression cycle.

https://doi.org/10.1371/journal.pone.0189412.t003

There were statistically significant deference between Group A and C, Group A and D, Group B and C in the sufficient CC depth ratio using the Wilcoxon signed-rank test as post-hoc analysis (P <0.01, P = 0.02, P = 0.02, respectively).

Among the secondary outcomes, we found the significantly higher rate of CC as the CC rest period was shorter. The median changes are 6, 4, 5, and 1 (times/min) in each group respectively (p < 0.01). Again, this change was significant for the female participants (p < 0.01) but not significant for the male participants (p = 0.48). No significant change in sufficient recoil ratio (p = 0.94) was observed.

Discussion

In this manikin-based randomized parallel trial, we found that rescuers with shorter CC rest period could not maintain CC with adequate depth during 30-min of CPR as compared to those with longer CC rest period. The median changes with regard to a sufficient CC depth ratio decreased by 4% for the two min interval group and by 3% for the four min interval group and these decreases can be 36% and 17%, respectively, according to the 25th percentile.

We consider that these changes can deteriorate the chances of survival, as many previous studies have shown that a subtle change in CC depth affects the outcome and even a slight decrease in CC depth can worsen the rate of return of spontaneous circulation [2, 9–11]. The decrease in sufficient CC ratio was dependent on the rest period; that is, a profound decrease was found in the shorter rest period group. This was consistent with the finding of previous studies, which found a time-dependent deterioration in CC. These studies suggested that rescuer fatigue plays an important role in the decline in CC quality[4, 6, 7]. In fact, several studies proved that rescuer fatigue can negatively affect the quality of CCs, by using physiological markers such as oxygen saturation by pulse oximetry, blood lactate concentration, heart rate, and neuromuscular function[12–14]. Our study also demonstrated that the rate of CC was higher as the CC rest period was shorter, confirming previous study results [2, 15–17]. This finding suggests that faster CC may be inducing rescuer fatigue and leads to poor sufficient CC depth ratio. As CC with pace-making devices such as metronome is known to maintain the adequate speed and depth of CCs[18, 19]. Using such devices during CPR might mitigate the harmful effects of shorter interval in relation to rescuer fatigue as well.

We found a significant decrease in sufficient CC ratio in the female subgroup but found no significant difference among any of the groups in the male subgroup. Previous studies have pointed out that female rescuers have more difficulty in maintaining the quality of CC than male rescuers possibly because of differences in the physical strength[20, 21].

Our study has several strengths. To the best of our knowledge, this is the first randomized controlled trial to determine the appropriate number of personnel to prevent the deterioration of CC quality. Several studies have shown a significant decline in the quality of CCs by consecutive performance due to rescuer fatigue, but the sufficient resting time for maintaining the quality during CPR has been unclear [4]. The finding of our study suggested that at least four personnel in a rescue team with 6 min rest period per person are necessary to maintain the quality of CC during 30 min of CPR.

Our study demonstrates good randomization, and no statistically significant differences were observed among groups A, B, C, and D with respect to age, body weight, height, CPR experience, duration of CPR training and regular exercise habits. In addition, we believe we were able to average the knowledge and skills of the participants through practical training and lectures by using a manikin just before the performance. Therefore, we can conclude that the lack of knowledge or skill had no role in our study results.

Our study also has some limitations. Firstly, most of our participants did not have sufficient clinical experience in CPR. In fact, none of our participants had official AHA BLS/ACLS certification. Thus, we should be careful in generalizing the results for clinically experienced rescuers. However, some previous studies showed that well-trained rescuers such as physicians in the emergency department and EMS also have difficulty maintaining the quality of CC [5, 22]. These findings may imply that well-trained rescuers also need a similar rest period between each CC.

Secondly, the quality of CC was defined based on the 2010 American Heart Association guideline for CPR and emergency cardiovascular care. The 2015 American Heart Association guideline recommends that the depth of CC should be more than five cm and less than six cm. We are unsure how the recommendations could or could not affects our results. Finally, this was a manikin-based study. The differences between the hardness of the chest of the manikin and that of a human must be considered, because this might affect rescuer fatigue.

Conclusion

According to our research, a 6 min interval after 2 min of CC is vital in order to sustain the quality of CC during a 30-min CPR cycle. Based on the 2015 AHA guidelines for CPR and emergency cardiovascular care[1, 23], rescuers are supposed to change their CC every 2 min during CPR. Hence, our study suggests that the favorable number of personnel for a 30-min CPR with good quality CC during in-hospital cardiac arrest is at least four when the rescue team consists of men and women.

Supporting information

Acknowledgments

We gratefully acknowledge all members of the emergency department of Fukui University Hospital for their helpful comments on the data analysis and study design.