Differences in the performance of resuscitation according to the resuscitation guideline terminology during infant cardiopulmonary resuscitation: "Approximately 4 cm" versus "at least one-third the anterior-posterior diameter of the chest".

AIM: This study was conducted to investigate the effect of resuscitation guideline terminology on the performance of infant cardiopulmonary resuscitation (CPR).
METHODS: A total of 40 intern or resident physicians conducted 2-min CPR with the two-finger technique (TFT) and two-thumb technique (TT) on a simulated infant cardiac arrest model with a 1-day interval. They were randomly assigned to Group A or B. The participants of Group A conducted CPR with the chest compression depth (CCD) target of "approximately 4 cm" and those of Group B conducted CPR with the CCD target of "at least one-third the anterior-posterior diameter of the chest". Single rescuer CPR was performed with a 15:2 compression to ventilation ratio on the floor.
RESULTS: In both chest compression techniques, the average CCD of Group B was significantly deeper than that of Group A (TFT: 41.0 [range, 39.3-42.0] mm vs. 36.5 [34.0-37.9] mm, P = 0.002; TT: 42.0 [42.0-43.0] mm vs. 37.0 [35.3-38.0] mm, P < 0.001). Adequacy of CCD also showed similar results (Group B vs. A; TFT: 99% [82-100%] vs. 29% [12-58%], P = 0.001; TT: 100% [100-100%] vs. 28% [8-53%], P < 0.001).
CONCLUSIONS: Using the CCD target of "at least one-third the anterior-posterior diameter of the chest" resulted in deep and adequate chest compressions during simulated infant CPR in contrast to the CCD target of "approximately 4 cm". Therefore, changes in the terminology used in the guidelines should be considered to improve the quality of CPR. TRIAL REGISTRATION: Clinical Research Information Service; cris.nih.go.kr/cris/en (Registration number: KCT0003486).

RCT Entities:   Population Interventions Outcomes

Introduction

Adequate chest compression depth (CCD) is one of the key components for improving survival rate of out-of-hospital cardiac arrest [1-3]. Recommended CCD for adult cardiac arrest patients had been adjusted from “at least 5 cm” to “approximately 5 cm” in the 2015 international consensus of International Liaison Committee on Resuscitation because Stiell et al. reported that maximum survival was expected in the depth interval from 40.3 to 55.3 mm (peak, 45.6 mm) [4-6]. These changes had influenced international guidelines [1–3, 7]. Although the 2015 American Heart Association and European Resuscitation Council guidelines maintained the recommended CCD as “at least 5 cm”, the 2015 Resuscitation Council of Asia and Korean guidelines for CPR changed the recommended CCD to “approximately 5 cm” according to the 2015 international consensus [3, 4, 7]. This discrepancy among the CPR guidelines confused both the instructors and trainees of CPR. Additionally, the word “approximately” might limit the chance of achieving adequate CCD. Indeed, Trethewey et al. reported recently that the performance of CCD decreased when the recommended CCD included the word “approximately” in contrast to the performance seen with “at least” during adult cardiac arrest simulation [8].

The CPR guidelines for infants recommend that the CCD should be “approximately 4 cm” or “at least one-third the anterior-posterior diameter of the chest” simultaneously [9-11]. We hypothesized that the CCD achieved following the CCD target of “approximately 4 cm” might be lower than CCD achieved following the CCD target “at least one-third the anterior-posterior diameter of the chest”. However, there was a possibility that the different terminologies for the CCD might affect other CPR performance variables such as hand position, chest compression rate, chest wall recoil, hands-off time, and ventilation parameters. Therefore, we also examined these parameters as secondary outcomes based on the different CCD terminologies used.

Materials and methods

Study ethics

The study protocol and informed consent form were approved by the Chung-Ang University Hospital Institutional Review Board on 3rd December 2018 (Approval number: 1803-012-347). The study was registered at the Clinical Research Information Service (cris.nih.go.kr/cris/en) on 11th February 2019 (Registration number: KCT0003486). The first participant was recruited on 22th February 2019 and the last on 17th August 2019. All participants provided written informed consent before participating in the study.

Study design

The present study was a prospective randomized simulation trial with parallel arms (Fig 1).

Fig 1

Study flow diagram.

CPR, cardiopulmonary resuscitation.

All participants conducted a 2-min CPR with the two-finger chest compression technique (TFT) and two-thumb encircling hands technique (TT) on a simulated infant cardiac arrest model. A wash out period of 1 day was provided between the experiments. Further, the study participants were randomized to Group A or B with a ratio of 1:1. Participants of Group A conducted all experiments with the CCD target of “approximately 4 cm” and those of Group B conducted all experiments with the CCD target of “at least one-third the anterior-posterior diameter of the chest”. Data were analysed after completion of all experiments.

Study participants

The inclusion criteria were as follows: intern or resident physicians who completed the basic life support course for healthcare professionals within 2 years in our hospital and decided to participate in the study voluntarily after receiving a complete description of the study protocol. Age, sex, and race were not considered as limitations for study participation. The exclusion criteria were as follows: doctors who could not conduct infant CPR because of injuries sustained to their hands or fingers within the last 2 weeks; doctors who declined participation in the study or withdrew their consent within the study period; and doctors who injured their hands or fingers during the experiments.

Study protocol

The experiments were conducted with an infant cardiac arrest simulation model involving a three-month-old-sized infant manikin (Resusci Baby QCPR, Laerdal Medical, Stavanger, Norway). The same manikin was used in all experiments. The anterior-posterior diameter of the chest of the manikin was 12 cm. The manikin was laid on the floor in the supine position. All experiments were performed with a CPR duration of 2 minutes, and with a chest compression-to-ventilation ratio of 15:2. Using a face shield, mouth-to-mouth ventilation was administered. The researcher who was in charge of data collection instructed the participants to use the index and middle fingers of the dominant hand when they used TFT for chest compressions, because the index and middle fingers (of the dominant hand) in combination are the most effective, second only to the two-thumb technique [12, 13]. Additionally, for all experiments, the position of the participants was standardized as follows: the right-handed participants were asked to sit on the right side of the manikin and the left-handed participants were asked to sit on the left side of the manikin in the kneeling position. The non-dominant hand was used to maintain head-tilt position during the chest compression period for TFT. Data were collected during the experiments by a sensor embedded in the manikin and were extracted through a computer (Simpad SkillReporter, Laerdal Medical). The Simpad screen was hidden and not visible to either the participant or the researcher.

Randomization method

The study participants were allocated randomly to Group A or B with stratified randomization method according to their sex for the purpose of allocating the participants in each group with the same ratio of sex. We controlled for sex based on the following reasons: the CCD for women rescuers was inferior to those of men rescuers because factors such as lower body weight and low level of muscular fitness could decrease CCD [14-17]. The present study was a randomized controlled trial that included minimal number of participants. Therefore, a difference in the sex ratio between the two groups might act as a potential confounder. As a result, two randomization lists were created through assignment of a random number (from 1 to 6) to six permuted blocks (1: AABB, 2: BBAA, 3: ABAB, 4: BABA, 5: ABBA, 6: BAAB) obtained through a computer program, with the initial letter of each group being either “A” or “B”.

Outcome variables

The primary outcome variable was average compression depth (ACD, mm). Secondary outcome variables were the ratio of correct hand position around lower half of sternum (correct hand position, %), total compressions (n), the ratio of chest compressions achieving chest compression depth over 38 mm (adequate depth, %), the ratio of complete chest wall recoil within 5 mm from baseline (complete recoil, %), average compression rate (n/min), the ratio of adequate chest compression rate between 100/min to 120/min (adequate rate, %), hands-off time (sec), total ventilations (n), and average ventilation volume (ml). Moreover, data on the characteristics of study participants, such as sex, age, position at the hospital, and dominant hand, were collected.

Sample size calculation

The ACD for TFT with the index and middle fingers of the right hand was 41.6 ± 1.1 mm and the ACD for TT was 43.1 ± 0.9 mm in a previous study [12]. We hypothesized that the ACD with a target CCD of “approximately 4 cm” would be lower than that with a target CCD of “at least one-third the anterior-posterior diameter of the chest” by as much as the standard deviation (1.1 mm for TFT and 0.9 mm for TT). The two-sided significance level was set at 0.05 and the statistical power was set at 80%. With a drop-out rate of 20%, the minimum number of study participants in each group was calculated to be 20 using a web-based program (Sample size calculator: two parallel-sample means). Thus, 40 participants were finally recruited.

Statistical analysis

All statistical analyses were performed using IBM SPSS Statistics, version 25.0 (IBM Corp., Armonk, New York, USA). Continuous variables were presented as mean ± standard deviation or median (interquartile range) according to the normality of the data distribution, whereas categorical variables were expressed as frequencies and percentages. The normality of the data distribution was analysed using the Shapiro-Wilk test or the Kolmogorov-Smirnov test. For normally distributed data, the two-sided independent sample t-test was used for the comparison of data between groups, otherwise, the Mann-Whitney U test was used. The difference between the categorical variables was assessed with the Pearson’s chi-squared test or Fisher’s exact test as appropriate. A P-value of less than 0.05 was considered statistically significant.

Results

Baseline characteristics

Overall, 40 intern or resident physicians were recruited and assigned randomly to the two groups (Group A = 20, Group B = 20). None of the participants were excluded. There were no significant differences in the sex, age, position at the hospital, specialities of the resident physician, and handedness between Groups A and B (Table 1).

Table 1

Characteristics of the study participant according to the study group.

Variables	Group A (n = 20)	Group B (n = 20)	P-value
Male sex (%)	15 (75.0)	15 (75.0)	1.000
Age (years)	27.5 (26.0, 29.0)	26.5 (25.0, 29.5)	0.529
Position			1.000
Resident physician	11 (55.0)	11 (55.0)
Intern physician	9 (45.0)	9 (45.0)
Specialities of the resident physician			0.830
Emergency Medicine	3 (27.3)	4 (36.4)
Internal Medicine	4 (36.4)	3 (27.3)
Pediatrics	2 (18.2)	0 (0.0)
General Surgery	0 (0.0)	2 (18.2)
Orthopedics	0 (0.0)	1 (9.1)
Dermatology	1 (9.1)	1 (9.1)
Psychiatrics	1 (9.1)	0 (0.0)
Right handedness (%)	18 (90.0)	19 (95.0)	1.000

Data are expressed as n (%) except for age, which is presented as median and interquartile range.

Comparisons between Group A and B

The ACDs of Group B were significantly deeper than those of Group A for both chest compression techniques (TFT: 41.0 [39.3–42.0] mm vs. 36.5 [34.0–37.8] mm, P = 0.002; TT: 42.0 [42.0–43.0] mm vs. 37.0 [35.3–38.0] mm, P < 0.001; Table 2, Fig 2). The proportion of trials wherein adequate depth was achieved was also significantly higher in Group B (TFT: 99% [82–100%] vs. 29% [12–58%], P = 0.001; TT: 100% [100–100%] vs. 28% [8–53%], P < 0.001). The proportion of trials where complete recoil was noted in Group B was significantly higher than that in Group A for TFT (98% [88–100%] vs. 87% [76–92%], P = 0.001). However, no significant difference in this regard was noted for TT (Table 2). Other variables, including correct hand position, total compressions, average compression rate, adequate rate, hands-off time, total ventilations, and average volume, were not significantly different between the groups.

Table 2

Comparisons of the variables according to the group.

Variables	Group A (n = 20)	Group B (n = 20)	P-value
Infant cardiopulmonary resuscitation using the two-finger chest compression technique
Correct hand position (%)	100 (100, 100)	100 (100, 100)	0.779†
Total compressions (n)	136 (129, 145)	144 (134, 150)	0.192†
Average compression depth (mm)	36.5 (34.0, 37.8)	41.0 (39.3, 42.0)	0.002†
Adequate depth (%)	29 (12, 58)	99 (82, 100)	0.001†
Complete recoil (%)	87 (76, 92)	98 (88, 100)	0.001†
Average compression rate (n/min)	120 ± 14	123 ± 16	0.480*
Adequate rate (%)	22 (2, 82)	6 (0, 45)	0.289†
Hands-off time (sec)	52 (50, 55)	50 (49, 54)	0.211†
Total ventilations (n)	16 (14, 18)	16 (14, 18)	0.659†
Average volume (ml)	41 (36, 44)	38 (32, 42)	0.383†
Infant cardiopulmonary resuscitation using the two-thumb encircling hands technique
Correct hand position (%)	100 (100, 100)	100 (100, 100)	0.799†
Total compressions (n)	136 (135, 149)	136 (135, 150)	0.820†
Average compression depth (mm)	37.0 (35.3, 38.0)	42.0 (42.0, 43.0)	<0.001†
Adequate depth (%)	28 (8, 53)	100 (100, 100)	<0.001†
Complete recoil (%)	12 (9, 19)	11 (9, 21)	0.698†
Average compression rate (n/min)	131 (129, 134)	130 (127, 140)	0.779†
Adequate rate (%)	1 (0, 9)	2 (0, 5)	0.242†
Hands-off time (sec)	53 ± 5	54 ± 4	0.888*
Total ventilations (n)	15 ± 3	16 ± 4	0.576*
Average volume (ml)	47 ± 7	49 ± 10	0.540*

P < 0.05 are presented in bold.

Group A: chest compression depth target of “approximately 4 cm”

Group B: chest compression depth target of “at least one-third the anterior-posterior diameter of the chest”

*Statistical significance was tested using two-sided independent sample t-test.

†Statistical significance was tested using Mann-Whitney U test.

Fig 2

Comparisons of average compression depths according to the group.

A. Two-finger chest compression technique (P = 0.002), B. Two-thumb encircling hands technique (P < 0.001).

Discussion

The results of the present study supported our hypothesis that the CCD according to the CCD target of “at least one-third the anterior-posterior diameter of the chest” was deeper than the CCD according to the CCD target of “approximately 4 cm”.

Deakin et al. also reported the performance of CPR according to different CCD targets [18]. Although the rescuers could discriminate the different CCD targets precisely, they did not achieve the target depths in all trials. We speculate that the target depth was not achieved because the depths were presented as ranges (e.g. 4.0–5.0 cm, 4.5–5.5 cm, and 5.0–6.0 cm). The rescuers might limit the force applied because of the upper margin of the target depth range. Considering these results, we hypothesized that if the term “approximately” is used to define the CCD, results similar to those seen when the CCD was defined as a range will be noted.

Previously, the 2005 guidelines recommended the CCD for adults as a range (Table 3) [19-21].

Table 3

Recommended chest compression depth in the international guidelines since 2005.

	2005	2010	2015
Recommended depth for adults
International consensus of ILCOR	At least 4–5 cm [19]	Al least 5 cm [5]	Approximately 5 cm [4]
ERC guideline	4–5 cm [20]	At least 5 cm (but not exceeding 6 cm) [22]	At least 5 cm (but not exceeding 6 cm) [2]
AHA guideline	Approximately 4–5 cm [21]	At least 5 cm [23]	At least 5 cm (but not exceeding 6 cm) [1]
Recommended depth for child
International consensus of ILCOR	Approximately 1/3 of the chest [24]	At least 1/3 of the chest or approximately 5 cm [25]	At least 1/3 of the chest or by 5 cm [26]
ERC guideline	Approximately 1/3 of the chest [27]	At least 1/3 of the chest or approximately 5 cm [28]	At least 1/3 of the chest or by 5 cm [9]
AHA guideline	Approximately 1/3-1/2 of the chest [21]	At least 1/3 of the chest or approximately 5 cm [29]	At least 1/3 of the chest or approximately 5 cm [10]
Recommended depth for infant
International consensus of ILCOR	Not evaluated	At least 1/3 of the chest or approximately 4 cm [25]	At least 1/3 of the chest or by 4 cm [26]
ERC guideline	Approximately 1/3 of the chest [27]	At least 1/3 of the chest or approximately 4 cm [28]	At least 1/3 of the chest or by 4 cm [9]
AHA guideline	Approximately 1/3-1/2 of the chest [21]	At least 1/3 of the chest or approximately 4 cm [29]	At least 1/3 of the chest or approximately 4 cm [10]

AHA, American Heart Association; ERC, European Resuscitation Council; ILCOR, International Liaison Committee on Resuscitation

This range-based definition of the recommended depth was subsequently removed from the 2010 guidelines [5, 22, 23]. Simultaneously, the recommended depth for the paediatric population was changed from “approximately 1/3 of the chest” to “at least 1/3 of the chest” [21, 24, 25, 27–30]. However, the term of “approximately” had not been completely removed from the guidelines, and “approximately 5 cm” or “approximately 4 cm” has been used since the 2010 guidelines were formulated. Although the International Liaison Committee on Resuscitation and European Resuscitation Council changed “approximately” to “by” in the 2015 paediatric guidelines, the term “approximately” remained in the 2015 American Heart Association guidelines [9, 10, 26]. Moreover, the term “by” might cause confusion in the same manner as with “approximately”.

The results of the present study showed that compared to “at least one-third the anterior-posterior diameter of the chest”, the term “approximately 4 cm” could significantly limit the CCD. The CCD has been reported to be usually higher with TT when compared to TFT [12, 31–34]. However, in this study, ACD and the proportion of cases wherein the adequate depth was achieved were significantly different between the groups for both TT and TFT (Fig 2).

Another interesting result was regarding the proportion of trials where complete recoil was noted with the TFT (Table 2). This result suggests that compared to the term “at least one-third the anterior-posterior diameter of the chest”, the term “approximately 4 cm” could limit the proportion of trials with complete recoil. However, similar results were not noted for TT. In case of TT, the proportion of trials with complete recoil were low in both groups, and these findings are consistent with those of a previous study [35]. However, we could not confirm why the proportion of trials with complete recoil with the TT was low in both the groups.

Previous studies have demonstrated that higher survival is associated with deeper CCD in the paediatric population [36]. Considering the negative (e.g. decreasing CCD) effect of the term “approximately 4 cm”, changes in the terminology used in the guidelines should be considered.

This study had several limitations that warrant mention. First, we recruited only medical doctors; therefore, our results cannot be generalised to other types of rescuers. Second, since the results of the present study were obtained from simulation experiments with a manikin, the results may not be identical to those obtained from CPR performed on humans. Third, we only compared two terminologies, i.e. “approximately” and “at least”, while “4 cm” and “one-third the anterior-posterior diameter of the chest” are also different. Therefore, there is a possibility that the term “one-third the anterior-posterior diameter of the chest” might have been attributable for the differences noted in the CCD between the groups in contrast to “4 cm”. However, the anterior-posterior diameter of the chest of the manikin was 12 cm, and thus, theoretically, “4 cm” and “anterior-posterior diameter of the chest” are the same. Nevertheless, the rescuers might perceive these two terms differently, and consequently, perform CPR in a different manner.

Conclusions

Using the CCD target of “at least one-third the anterior-posterior diameter of the chest” resulted in deep and adequate chest compressions during infant CPR when compared to with the CCD target of “approximately 4 cm”. Therefore, changes in the terminology used in the guidelines should be considered to improve the quality of CPR.

(XLSX)

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24 Jan 2020

PONE-D-19-34142

Differences in the performance of resuscitation according to the resuscitation guideline terminology during infant cardiopulmonary resuscitation: “approximately 4 cm” versus “at least one-third the anterior-posterior diameter of the chest”

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Reviewer #1: 1. In line 49, what is being referred to as the “same problem”? Is it the confusion that is detailed in Lines 44-45, or the decrease performance of CCD referred to in lines 45-48, or both?

2. In Line 51, “the quality of CPR” is not explicitly defined as what the study designates to determine what “quality” is/means.

3. The hypothesis, lines 51-55, states the belief that one CCD target will result in “lower” quality of CPR than the other CCD target. As the hypothesis lays out the objective of proving one being lesser than the other, the data, analysis, and discussion is based upon the context of one being better than the other. Although this is one in the same, it would be more consistent to present the information uniformly (i.e. discussing how one CCD target is of lower quality rather than of higher quality vs. stating a hypothesis that one CCD target is of better quality than the other).

4. Under Study Participants, line 74-75 states that “Age, sex, and race were not considered as limitations for study participations.” However, under Randomization Method, lines 104-105, groups were randomized by stratifying according “to their sex for the purpose of allocating the participants in each group with the same ratio of sex.” Is not sex, therefore, an inclusion criterion for study participation if the aim of randomization of the groups were to make sure the sex ratio was equivalent? If no participants were dropped, then was those recruiting participants aware and/or considering the number of males and females that were approached and volunteered for the study?

5. “Quality,” again, has not been defined for this study. Therefore, when discussing quality, as is in Lines 191-192, in comparison to the quality of chest compression in other studies, it becomes difficult for the reader to understand the comparison/contrast being made. Please define what the study indicates as “quality CPR” and “quality chest compressions”

6. Caution when using the term “significantly.” In lines 198-200, when using the phrase “significantly lower” it eludes to the reader that there was a statistically significant (P < 0.05) outcome where in fact the authors are stating the opposite. For example one can say based on the findings of this study that there was no statistical difference between groups A and B for complete recoil and the proportion of trials where complete recoil was noted was fewer than that required for overall high quality CPR, which is consistent to a previous study. Not that, line 198, “was significantly lower than that required for high quality CPR...”

7. Lines 201-202, “…the risk of injury might be increased when using the term “at least” contradicts the study’s conclusions and hypothesis. If stating/concluding Group B, with CCD target of “at least”, was better than Group A, CCD target of “approximately”, then by having Lines 201-202 causes doubt and conflicting view point. Be careful on wording in addressing this point.

8. Based on the third limitation outlined in Lines 208-214, the issue in the discussion and conclusion is that one cannot state that the use of “approximate” vs “at least” being better than the other, as the author has done, without accounting for confounding variables which is the entire phrase of the CCD target. One cannot conclude, based on the study design and data presented, that the differences between the groups were to “approximate” vs “at least” or “one third the anterior-posterior diameter of the chest” vs “4 cm.” It can only be discussed/concluded on the entire phrase itself and not to the segments within the phrase. Would therefore remove the context around Lines 190-191 and Lines 195-197.

Reviewer #2: PONE-D-19-34142: statistical review

SUMMARY. This study estimates the effect of two resuscitation guidelines on the performance of infant cardiopulmonary resuscitation, measured in terms of average compression depth (ACD; primary outcome) and a battery of secondary outcomes. I have some concerns about the definition of the variables under study (major issue 1), the presentation of the results (major issue 2) and, finally, a possible limitation of the study (major issue 3)

MAJOR ISSUES

1. Lines 110-115. The description of the secondary outcomes is a bit cryptic. For example, how is "correct hand position" defined? What does the number of total compressions measure? When is depth "adequate"? When is recoil "complete"? A detailed description of the outcomes under study is not only a courtesy to the readers (such as me) who are not necessarily experts of resuscitation methods, but it also allows results reproducibility. In addition, in which sense do these variables measure resuscitation performance?

2. In the statistical analysis section, the authors correctly say that they use the Chi-square tests or Fisher exact tests to compare proportions. However, in Table 2 differences between proportions are incorrectly tested using the Mann-Whitney U test (at least this is what the note of the table says). Please clarify.

3. Lines 89-90: the same manikin was used in all the experiments. Isn't this a limitation of the study? Shouldn't one exploit manikins of different sizes to robustify the results? Please clarify this point.

Reviewer #3: The methodology appears to be sound, and the results do appear to be consistent with the data (supplemental data).

Their statistical analysis plan appears to be appropriate as well. Though I wish they would have described or mentioned what data was normally distributed or not.

It appears that it was only interns or residents that participated in the study. I would have mentioned this in the study, instead of saying medical doctors.

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Reviewer #1: Yes: Adnan Mesiwala, DO

Reviewer #2: No

Reviewer #3: No

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30 Jan 2020

30 January 2020

Kevin Ching, MD

Academic Editor

PLOS ONE

Dear Editor,

I wish to re-submit the manuscript titled “Differences in the performance of resuscitation according to the resuscitation guideline terminology during infant cardiopulmonary resuscitation: “approximately 4 cm” versus “at least one-third the anterior-posterior diameter of the chest”.” The manuscript ID is PONE-D-19-34142.

We thank you and the reviewers for your thoughtful suggestions and insights. The manuscript has benefited from these insightful suggestions. I look forward to working with you and the reviewers to move this manuscript closer to publication in PLOS ONE. The manuscript has been rechecked and the necessary changes have been made in accordance with the reviewers’ suggestions. Thank you for your consideration. I look forward to hearing from you.

Sincerely,

Je Hyeok Oh, MD, PhD

Department of Emergency Medicine,

Chung-Ang University College of Medicine,

84 Heukseok-ro, Dongjak-gu, Seoul 06974, Republic of Korea

Tel. no.: +82 2 6299 1820

Fax no.: +82 2 6264 1119

Email address: jehyeokoh@cau.ac.kr

Our response to the comments of the Reviewer #1:

1. In line 49, what is being referred to as the “same problem”? Is it the confusion that is detailed in Lines 44-45, or the decrease performance of CCD referred to in lines 45-48, or both?

Answer) Thank you for your comments. The problem refers to the fact that the guideline of cardiopulmonary resuscitation used both terminologies “at least” and “approximately” simultaneously. We have deleted the sentence to avoid misinterpretation.

2. In Line 51, “the quality of CPR” is not explicitly defined as what the study designates to determine what “quality” is/means.

Answer) Thank you for your comments. Our study focused on whether the different terminologies might affect the chest compression depth. Therefore, we changed the phrase “the quality of CPR” to “the chest compression depth” to clarify the hypothesis.

3. The hypothesis, lines 51-55, states the belief that one CCD target will result in “lower” quality of CPR than the other CCD target. As the hypothesis lays out the objective of proving one being lesser than the other, the data, analysis, and discussion is based upon the context of one being better than the other. Although this is one in the same, it would be more consistent to present the information uniformly (i.e. discussing how one CCD target is of lower quality rather than of higher quality vs. stating a hypothesis that one CCD target is of better quality than the other).

Answer) Thank you for your comments. The primary goal of the present study was to compare the chest compression depth (CCD) achieved based on the different terminologies used for defining the CCD. Therefore, we arranged the text of the manuscript so that it focuses on the CCD. However, there was a possibility that the different terminologies for the CCD might affect other CPR performance variables such as hand position, chest compression rate, chest wall recoil, hands-off time, and ventilation parameters. Therefore, we also examined these variables as secondary outcome based on the different CCD terminologies used.

4. Under Study Participants, line 74-75 states that “Age, sex, and race were not considered as limitations for study participations.” However, under Randomization Method, lines 104-105, groups were randomized by stratifying according “to their sex for the purpose of allocating the participants in each group with the same ratio of sex.” Is not sex, therefore, an inclusion criterion for study participation if the aim of randomization of the groups were to make sure the sex ratio was equivalent? If no participants were dropped, then was those recruiting participants aware and/or considering the number of males and females that were approached and volunteered for the study?

Answer) Thank you for your comments. Although we did not limit the participants based on age, sex, and race, we used a stratified allocation method based on sex with the purpose of controlling for participant’s sex between the groups. We controlled for sex based on the following reasons: the chest compression depth (CCD) for women rescuers was inferior to those of men rescuers (Hansen et al. PMID: 21629121) because factors such as lower body weight and low level of muscular fitness could decrease CCD (Krikscionaitiene et al. PMID: 22345324, Oh et al. PMID: 27624370, Lopez-Gonzalez et al. PMID: 27344099). The present study was a randomized controlled trial that included a minimal number of participants (n = 40). Therefore, a difference in the sex ratio between the two groups might act as a potential confounder. We have added the reason for using stratified allocation in the methods section.

Although the researcher in charge of collecting data knew the allocated sequence, we did not determine the number of men or women participants prior to starting data collection. We assigned the participants to the groups according to their sex using two randomization lists. The randomization lists were included in the supplementary file (S1 Data set.xlsx). Therefore, the participants also did not know the number of men or women participants and were blinded to the allocation of the group.

5. “Quality,” again, has not been defined for this study. Therefore, when discussing quality, as is in Lines 191-192, in comparison to the quality of chest compression in other studies, it becomes difficult for the reader to understand the comparison/contrast being made. Please define what the study indicates as “quality CPR” and “quality chest compressions”

Answer) Thank you for your comments. The quality of cardiopulmonary resuscitation (CPR) is defined by five key factors required for high quality CPR such as chest compressions of adequate rate, chest compressions of adequate depth, full chest recoil between compressions, minimizing interruptions in chest compressions, and avoiding excessive ventilation (Kleinman et al. PMID: 26472993). However, we agree with the reviewer’s concern that there would be confusions in the interpretation of “quality of CPR”. Therefore, as recommended, we have replaced the term “quality of CPR” with “chest compression depth”.

6. Caution when using the term “significantly.” In lines 198-200, when using the phrase “significantly lower” it eludes to the reader that there was a statistically significant (P < 0.05) outcome where in fact the authors are stating the opposite. For example one can say based on the findings of this study that there was no statistical difference between groups A and B for complete recoil and the proportion of trials where complete recoil was noted was fewer than that required for overall high quality CPR, which is consistent to a previous study. Not that, line 198, “was significantly lower than that required for high quality CPR...”

Answer) Thank you for your comments. We used the term “significantly” to denote extremely low values (the ratio of complete recoil was only 11-12%). However, we agree with the reviewer’s concern. Therefore, we have revised the sentence to state “the proportion of trials with complete recoil were low in both groups”.

7. Lines 201-202, “…the risk of injury might be increased when using the term “at least” contradicts the study’s conclusions and hypothesis. If stating/concluding Group B, with CCD target of “at least”, was better than Group A, CCD target of “approximately”, then by having Lines 201-202 causes doubt and conflicting view point. Be careful on wording in addressing this point.

Answer) Thank you for your comments. We have revised the sentence as “Previous studies have demonstrated that higher survival is associated with deeper CCD in the paediatric population. Considering the negative effects (e.g. decreasing CCD) of defining CCD using the term “approximately”, changes in the terminology used for the guidelines should be considered.”.

8. Based on the third limitation outlined in Lines 208-214, the issue in the discussion and conclusion is that one cannot state that the use of “approximate” vs “at least” being better than the other, as the author has done, without accounting for confounding variables which is the entire phrase of the CCD target. One cannot conclude, based on the study design and data presented, that the differences between the groups were to “approximate” vs “at least” or “one third the anterior-posterior diameter of the chest” vs “4 cm.” It can only be discussed/concluded on the entire phrase itself and not to the segments within the phrase. Would therefore remove the context around Lines 190-191 and Lines 195-197.

Answer) Thank you for your comments. We agree with the reviewer’s concern. Instead of removing the sentence, we have revised the sentences as follows: “The results of the present study showed that the term ‘approximately 4 cm’ could significantly limit the CCD when compared to ‘at least one-third the anterior-posterior diameter of the chest.’ This result suggests that compared to the term ‘at least one-third the anterior-posterior diameter of the chest’, the term ‘approximately 4 cm’ could limit the proportion of trials with complete recoil in addition to CCD.

Our response to the comments of the Reviewer #2:

1. Lines 110-115. The description of the secondary outcomes is a bit cryptic. For example, how is "correct hand position" defined? What does the number of total compressions measure? When is depth "adequate"? When is recoil "complete"? A detailed description of the outcomes under study is not only a courtesy to the readers (such as me) who are not necessarily experts of resuscitation methods, but it also allows results reproducibility. In addition, in which sense do these variables measure resuscitation performance?

Answer) Thank you for your comments. We agree with the reviewer’s concern. We have revised the sentence for describing secondary outcome variables as “Secondary outcome variables were the ratio of correct hand position around lower half of sternum (correct hand position, %), total compressions (n), the ratio of chest compressions achieving chest compression depth over 38 mm (adequate depth, %), the ratio of complete chest wall recoil within 5 mm from baseline (complete recoil, %), average compression rate (n/min), the ratio of adequate chest compression rate between 100/min to 120/min (adequate rate, %), hands-off time (sec), total ventilations (n), and average ventilation volume (ml).” All parameters were measured by the embedded sensors within the infant manikin (Resusci Baby QCPR, Laerdal Medical, Stavanger, Norway) and transferred to the mobile laptop computer (Simpad SkillReporter, Laerdal Medical). Adequacy of parameters such as depth limit of adequate depth and complete recoil was determined by the manufacturer (Laerdal Medical). However, the range of adequate depth, rate, and location of chest compression were recommended by the cardiopulmonary resuscitation (CPR) guidelines. We evaluated these parameters because these parameters (e.g. adequate depth, adequate rate, complete recoil, minimizing hand-off time, adequate ventilation volume) were recommended by the guideline when defining high quality CPR (Kleinman et al. PMID: 26472993).

2. In the statistical analysis section, the authors correctly say that they use the Chi-square tests or Fisher exact tests to compare proportions. However, in Table 2 differences between proportions are incorrectly tested using the Mann-Whitney U test (at least this is what the note of the table says). Please clarify.

Answer) Thank you for your comments. All variables included in table 2 are continuous variables. Therefore, we compared the variables using two-sided independent sample t-test or Mann-Whitney U test. We used the Chi-square tests or Fisher exact tests for analysing categorical variables in Table 1. Please, check the data in the supplementary file (S1 Data set.xlsx).

3. Lines 89-90: the same manikin was used in all the experiments. Isn't this a limitation of the study? Shouldn't one exploit manikins of different sizes to robustify the results? Please clarify this point.

Answer) Thank you for your comments. Theoretically, the reviewer’s comment is accurate. However, the limitation of using the same manikin model is included in the limitations of the simulation trial. In addition, using various kinds of manikin models or different manikin models can be a confounder. For example, if we conducted a laboratory experiment with different animal models or different experimental tools, the validity of the study results would be doubtful. Although the present study was a human trial, the nature of the methodology was experimental.

Our response to the comments of the Reviewer #3:

1. Their statistical analysis plan appears to be appropriate as well. Though I wish they would have described or mentioned what data was normally distributed or not.

Answer) Thank you for your comments. Instead of describing the normal distribution of data, we showed the method of statistical methods at the bottom of the table. For example, the data analysed by using two-sided independent sample t-test were normally distributed and the data analysed by using Mann-Whitney U test were not normally distributed.

2. It appears that it was only interns or residents that participated in the study. I would have mentioned this in the study, instead of saying medical doctors.

Answer) Thank you for your comments. We have revised the term “medical doctors” to “intern or resident physicians” as recommended. Thank you.

Sincerely yours,

Je Hyeok Oh, MD, PhD

Submitted filename: Response to the reviewers comments.docx

Click here for additional data file.

3 Mar 2020

PONE-D-19-34142R1

Differences in the performance of resuscitation according to the resuscitation guideline terminology during infant cardiopulmonary resuscitation: “approximately 4 cm” versus “at least one-third the anterior-posterior diameter of the chest”

PLOS ONE

Dear Prof. Oh,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

==============================

Thank you for your edits. The revised manuscript has addressed our concerns. One minor additional question: What specialty of interns and residents were enrolled? We only know that they were certified in BLS. It is possible that the specialty of residents might impact on their CCD. For instance, a pediatric resident (who has more confidence with children) might be more aggressive than an internal medicine resident, leading to deeper compressions by the pediatric residents. If the distribution of different specialities between Group A and B are unequal, this could bias the results.==============================

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4 Mar 2020

4 March 2020

Kevin Ching, MD

Academic Editor

PLOS ONE

Dear Editor,

I wish to re-submit the manuscript titled “Differences in the performance of resuscitation according to the resuscitation guideline terminology during infant cardiopulmonary resuscitation: “approximately 4 cm” versus “at least one-third the anterior-posterior diameter of the chest”.” The manuscript ID is PONE-D-19-34142_R1.

We thank you and the reviewers for your thoughtful suggestions and insights. The manuscript has benefited from these insightful suggestions. I look forward to working with you and the reviewers to move this manuscript closer to publication in PLOS ONE. The manuscript has been rechecked and the necessary changes have been made in accordance with the reviewers’ suggestions. Thank you for your consideration. I look forward to hearing from you.

Sincerely,

Je Hyeok Oh, MD, PhD

Department of Emergency Medicine,

Chung-Ang University College of Medicine,

84 Heukseok-ro, Dongjak-gu, Seoul 06974, Republic of Korea

Tel. no.: +82 2 6299 1820

Fax no.: +82 2 6264 1119

Email address: jehyeokoh@cau.ac.kr

Our response to the comments of the Reviewer #1:

1. Thank you for your edits. The revised manuscript has addressed our concerns. One minor additional question: What specialty of interns and residents were enrolled? We only know that they were certified in BLS. It is possible that the specialty of residents might impact on their CCD. For instance, a pediatric resident (who has more confidence with children) might be more aggressive than an internal medicine resident, leading to deeper compressions by the pediatric residents. If the distribution of different specialities between Group A and B are unequal, this could bias the results.

Answer) Thank you for your valuable comments. We have revised the manuscript according to the reviewer’s recommendation. In detail, there were no specialities in the intern physician. In South Korea, intern physicians rotate all clinical fields (specialities) for one year before starting the course of resident physician. Therefore, we have compared whether there was a difference in the specialities of the resident physician according to the groups. As a result, there were no differences in the distribution of specialities between Group A and B. We have added the results in the table 1.

Submitted filename: Response to the reviewers comments.docx

Click here for additional data file.

6 Mar 2020

Differences in the performance of resuscitation according to the resuscitation guideline terminology during infant cardiopulmonary resuscitation: “approximately 4 cm” versus “at least one-third the anterior-posterior diameter of the chest”

PONE-D-19-34142R2

Dear Dr. Oh,

We are pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it complies with all outstanding technical requirements.

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With kind regards,

Kevin Ching, M.D.

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

11 Mar 2020

PONE-D-19-34142R2

Differences in the performance of resuscitation according to the resuscitation guideline terminology during infant cardiopulmonary resuscitation: “approximately 4 cm” versus “at least one-third the anterior-posterior diameter of the chest”

Dear Dr. Oh:

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on behalf of

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PLOS ONE