a b s t r a c t

Objective: The posture of the rescuer while performing the one-handed chest compression (OHCC) has not yet been evaluated. This study aimed to investigate the effect of vertical compression during pediatric cardiopulmo- nary resuscitation (CPR) using the OHCC technique.

Methods: This was a prospective randomized crossover simulation trial. A total of 42 medical doctors conducted a 2-min single-rescuer CPR using the conventional OHCC (Test 1) or vertical OHCC (Test 2) technique on a Pediatric manikin. The chest compression and Ventilation parameters were measured in real time during the experiments using sensors embedded in the manikin. In addition, the compression force of each technique was measured using a force plate.

Results: The average and adequate chest compression depth (CCD) were significantly higher in Test 2 than in Test 1 (average depth: 54.0 mm (interquartile range [IQR]: 48.5-56.0) in Test 2 vs. 49.0 mm (IQR: 40.0-54.0) in Test 1, P < 0.001; adequate depth: 99.0% (IQR: 36.3-100.0) in Test 2 vs. 52.0% (IQR: 0.0-98.0) in Test 1, P < 0.001). The

average force of compression was also significantly higher in vertical OHCC than that in conventional OHCC (25.7 kg +- 4.4 in vertical OHCC vs. 24.5 kg +- 4.2 in conventional OHCC, P < 0.001). The ventilation parameters were not significantly different between Tests 1 and 2.

Conclusions: The vertical OHCC could provide a deeper and more adequate CCD compared with the conventional OHCC, and the advantages of the vertical OHCC originate from the superiority of the compression force.

(C) 2022

1. Introduction

Rescuers can use either a one-handed (one-handed chest compression [OHCC] technique) or two-handed (two-handed chest compression [THCC]) technique during pediatric cardiopulmonary re- suscitation (CPR) depending on the size and hand span [1]. Although THCC has been associated with deeper chest compression depth and compression force in manikin studies, no clinical data are available to determine whether OHCC or THCC produces better out- comes for children receiving CPR [2-4].

The method and posture of THCC are well known because this technique is used simultaneously in adult cardiac arrest victims. How- ever, the method and posture of OHCC have not been well described in the guidelines owing to the lack of evidence. Although the guidelines

* Corresponding author at: Department of Emergency Medicine, Chung-Ang University College of Medicine, 84 Heukseok-ro, Dongjak-gu, Seoul 06974, Republic of Korea.

E-mail addresses: [email protected] (J.H. Oh), [email protected] (H. Noh), [email protected] (J.G. Lee), [email protected] (D.-K. Kim).

from the European resuscitation council indicated that the rescuer could use the other hand to maintain an airway or stabilize the compression arm at the level of the elbow when performing the OHCC, the posture of the compression arm has not been described [1]. Two studies evalu- ated the effect of posture modification during continuous OHCC [5,6]. These studies modified the posture of OHCC in two steps. First, the axis of the rescuer’s compression arm was adjusted to compress the lower half of the sternum vertically. Second, the opposite hand was wrapped around the elbow joint of the rescuer’s compression arm. The results supported that these modifications in the posture of OHCC could maintain a deeper average CCD than those of conventional OHCC [5]. However, whether a deeper average CCD can be achieved from vertical compression due to the simultaneous adjustments of the two steps (vertical compression and stabilization of the elbow joint) could not be determined. Hence, we hypothesized that posture modifi- cation, that is, vertical chest compression, might improve CCD during OHCC (Fig. 1). In addition, this improvement in the CCD might be due to the higher power of the vertical compression compared with that of conventional OHCC. If a deeper CCD is achieved by vertical compression,

https://doi.org/10.1016/j.ajem.2022.06.044

0735-6757/(C) 2022

Fig. 1. Postures during one-handed chest compression.

A: Posture during conventional one-handed chest compression. B: Posture during vertical one-handed chest compression.

the other hand can be used to maintain the airway. Hence, this study aimed to investigate the effects of vertical compression during pediatric CPR using an OHCC.

1. Methods
   1. Study design

This study was a prospective, randomized crossover simulation trial (Fig. 2). The participants in group A performed a 2-min CPR using

conventional OHCC (Test 1). After passing the washout period of 1 day, they performed a 2-min CPR using vertical OHCC (Test 2). The participants in group B followed the trial sequence in reverse order. The chest compression forces of both techniques were measured after completion of Tests 1 and 2.

• 1. Study participants

Medical doctors who were members of the CPR team at our hospital voluntarily participated in the study after receiving a complete

Fig. 2. Study flow diagram.

CPR, cardiopulmonary resuscitation.

description of the study protocol. Participants who could not perform CPR due to arm or hand injuries within the past two weeks, declined to participate in the study, and injured their arms or hands during the experiments were excluded. participant recruitment was started on April 13, 2021 and ended on November 21, 2021.

• 1. Posture modification

To enhance the quality of the OHCC, the axis of the chest compres- sion arm was adjusted to the chest compression area to maximize the rescuer’s weight load by compressing the sternum vertically (Fig. 1) [7-9].

• 1. Study protocol

The experiments were conducted with a child cardiac arrest simula- tion model using a 5-year-old-sized pediatric manikin (Resusci Junior QCPR; Laerdal Medical, Stavanger, Norway). The manikin was placed on the floor in supine position. All experiments were performed with a CPR duration of 2 min and chest compression-to-ventilation ratio of 30:2. mouth-to-mouth ventilation was administered using a face shield. CPR-prompting devices such as a metronome were not used during the experiments as these types of devices can affect the CCD [10,11]. For all experiments, the positions of the participants were standardized as fol- lows: right-handed participants were placed on the right side of the manikin, whereas left-handed participants were placed on the left side of the manikin. The non-dominant hand was used to maintain the head-tilt position during the chest compression period when the OHCC technique was used in pediatric CPR (Fig. 1). Data were collected in real time during the experiments using a sensor embedded in the manikin and were extracted using a computer (SimPad PLUS with SkillReporter, Laerdal Medical). The rescuers were not allowed to view their performance on the SimPad screen during the experiments. After the completion of the experiments, all participants measured the com- pression forces of the conventional and vertical OHCC. Compression forces were measured using force plates (Biometrics, Newport, UK) in the E-LINK Evaluation System (Biometrics) and E-LINK Evaluation and Exercise Systems, version 13 software (Biometrics). The strength of each technique was described as the average value of the five consecu- tive chest compressions.

• 1. Randomization method

The study participants were randomly assigned to groups A and B using a randomization list created with random number sequences ob- tained using a web-based program. Six permuted blocks labeled with the letter assigned to each group (“A” or “B”) were matched according to the random number sequence (1: AABB, 2: BBAA, 3: ABAB, 4: BABA, 5: ABBA, and 6: BAAB). To control the sex ratio between groups A and B, two randomization lists were created for each sex (randomization list 1 for men and list 2 for women). The randomization list was created on March 20, 2021.

• 1. Outcome variables

The primary outcome variable was the average CCD (mm). The sec- ondary variables were the ratio of correct hand position (%), number of total chest compressions (number), ratio of adequate depth (%), ratio of complete recoil (%), average chest compression rate (compressions/ min), ratio of adequate rate (%), hands-off time (s), number of total ven- tilations (number), average Ventilation volume (mL), and average force (kg). In addition, data on the study participants’ characteristics, such as sex, age, position at the hospital, and handedness (right or left), were collected.

• 1. Sample size calculation

The sample size was calculated based on a previous study that evaluated the effect of metronome guidance on OHCC using the same Simulation model [10]. In a previous study, the average CCD during OHCC without metronome feedback was 52.7 +- 5.7 mm [10]. A signifi- cant difference was defined as 50% of the standard deviation in a previ- ous study (CCD of 2.85 mm). The population variance was set to 5.7². The two-sided significance level was set at 0.05, while the statistical power was set at 80%. The minimum number of study participants in each group was calculated using a web-based program (sample size calculator: two crossover-sample means) and was determined to be 16 individuals [12]. Thus, 32 participants were required to test our hy- pothesis.

• 1. Statistical analysis

All statistical analyses were performed using SPSS Statistics (version 26.0; IBM Corp., Armonk, New York, USA). Continuous variables were expressed as mean +- standard deviation or median (interquartile range) according to the normality of the distribution, whereas categor- ical variables were expressed as frequencies and percentages. The normality of the distribution was analyzed using the Shapiro-Wilk test and Kolmogorov-Smirnov test. The data between Test 1 and Test 2 were compared using the paired t-test or Wilcoxon signed-rank test, according to the normality of the distribution. The difference between categorical variables was determined using Pearson’s chi-square test or Fisher’s exact test, as appropriate. Statistical significance was set at P < 0.05.

• 1. Ethics statement

The study protocol was approved by the Institutional Review Board of our hospital on March 10, 2021 (approval number: 2111-005-449). All participants provided written informed consent prior to their partic- ipation in the study.

1. Results
   1. Baseline characteristics

A total of 42 medical doctors were recruited and randomly assigned to two groups. None of the participants was excluded from the study. The average age of the participants was 26.0 (25.0-29.0) years. Most of the participants were men (32/42 [76.2%]) and right-handed (41/42 [97.6%]). No significant intergroup differences were observed in terms of age, sex, position at hospital, or handedness (Table 1).

Table 1

Baseline characteristics.

Group	Group A (n = 25)	Group B (n = 17)	P value
Average age (years)	26.0 (25.0-28.0)	26.0 (25.0-29.0)	0.896
Male sex	20/25 (80.0%)	12/17 (70.6%)	0.482
1Resident physician	7/25 (28.0%)	5/17 (29.4%)	0.921
Specialty			0.947
Emergency medicine	3/7 (42.9%)	3/5 (60.0%)
Internal medicine	0/7 (0.0%)	1/5 (20.0%)
General surgery	1/7 (14.3%)	0/5 (0.0%)
Neurosurgery	0/7 (0.0%)	1/5 (20.0%)
Obstetrician	1/7 (14.3%)	0/5 (0.0%)
Otolaryngologist	1/7 (14.3%)	0/5 (0.0%)
Radiologist	1/7 (14.3%)	0/5 (0.0%)
Right-handed	24/25 (96.0%)	17/17 (100.0%)	1.000

¹ Other position was an “intern physician.”

Table 2

Comparisons of the parameters between the conventional one-handed chest compression technique and vertical one-handed chest compression technique.

addition, the average hands-off time of vertical OHCC was significantly lower than that of conventional OHCC (Table 2). The ventilation param- eters were not significantly different between Tests 1 and 2 (Table 2).

Test Test 1 (conventional

OHCC)

Test 2 (vertical OHCC)

P value

The average compression force of the vertical OHCC was significantly higher than that of the conventional OHCC (Table 2 and Fig. 3).

(n = 42) (n = 42)

correct hand position (%) 100.0 (98.3-100.0) 100.0 (100.0-100.0) 0.011

1. Discussion

Total compressions (number)

151.5 (147.5-163.0) 153.0 (149.5-168.0) 0.051

Average depth (mm) 49.0 (40.0-54.0) 54.0 (48.5-56.0) <0.001

Adequate depth (%) 52.0 (0.0-98.0) 99.0 (36.3-100.0) <0.001

Complete recoil (%) 100.0 (95.8-100.0) 100.0 (99.0-100.0) 0.013

Average rate (/min) 106.5 (99.0-113.0) 106.5 (102.3-114.3) 0.199

Adequate rate (%) 93.0 (42.8-98.0) 96.0 (46.8-99.0) 0.280

Hands-off time (s) 10.0 (8.0-10.3) 8.5 (7.0-10.0) 0.001

Total ventilation (number) 8.0 (6.0-9.0) 9.0 (7.8-10.0) 0.102

The results of the present study support our hypothesis that the

average CCD of vertical OHCC is significantly deeper than that of con- ventional OHCC, and this advantage of the vertical OHCC is related to the superiority of the compression force.

These results could be expected because the main determinant of the CCD, that is, the chest compression force, is proportional to the res-

Average ventilation

volume (mL)

152.7 +- 54.4 154.6 +- 63.8 0.727

cuer’s upper body mass [7-9,13,14]. To maximize the effect of the res-

cuer’s upper body mass, vertical compression is required. However,

Average force (kg) 24.5 +- 4.2 25.7 +- 4.4 <0.001

P values of <0.05 are presented in bold. OHCC, one-handed chest compression.

3.2. Test 1 (conventional one-handed chest compression) versus test 2 (ver- tical one-handed chest compression)

The average CCD of the conventional OHCC was significantly lower than that of the vertical OHCC (Table 2 and Fig. 3). The adequacy of chest compressions was also superior in vertical OHCC (Table 2). In

whether the ratio of complete recoil would decrease when the vertical OHCC was used remained a concern as there was a trade-off relation- ship between CCD and chest wall recoil. Moreover, no deterioration was observed in the ratio of complete recoil when vertical OHCC was used. The ratio of complete recoil in vertical OHCC was significantly higher than that in conventional OHCC (Table 2).

Another interesting result was a shorter hands-off time during verti- cal OHCC compared with that during conventional OHCC (Table 2). This result was unexpected, and the exact reason for the shorter hands-off time during vertical OHCC remains unknown. The distance between the mouth of the pediatric manikin and the mouth of the rescuer was

Fig. 3. Comparisons of average chest compression depths and compression forces between the conventional one-handed chest compression technique and the vertical one-handed chest compression technique.

COHCC, conventional one-handed chest compression; VOHCC, vertical one-handed chest compression.

Fig. 4. The posture of the modified one-handed chest compression technique.

relatively shorter during vertical OHCC than during conventional OHCC (Fig. 1). This difference in distance between the manikin’s mouth and rescuer’s mouth might contribute to the short hands-off time during vertical OHCC. Although the number of total compressions did not differ statistically between the conventional and vertical OHCC, the shorter hands-off time might be another advantage of vertical OHCC.

The vertical OHCC could be a standard posture when performing the OHCC as all parameters of the experiments supported that the vertical OHCC was superior to the conventional OHCC. However, another study is warranted to determine whether the vertical OHCC is superior to the modified OHCC reported in previous studies or not [5,6]. Simple modification of the vertical OHCC would be a better option because the other hand could be used to maintain the victim’s airway during vertical OHCC. If the modified OHCC reported in previous studies (vertical compression plus elbow stabilization) could produce a higher compression force than the vertical OHCC, it would be a better option in the in-hospital setting because the airway could be maintained by an- other CPR team member (Fig. 4). Further studies comparing the chest compression force between the vertical OHCC and the modified OHCC are needed to establish this strategy.

In case of complications associated with CPR such as sternal or rib fracture, the possibility of complication might be increased when using the vertical OHCC compared with using the conventional OHCC because of the difference in the compression power. However, consider- ing the clinical data supporting that deeper CCD was associated with higher survival compared to shallower CCD, we believe that the vertical OHCC might be a better option for cardiac arrest children compared with the conventional OHCC [15].

This study had several limitations. First, only medical doctors were recruited in this study. Therefore, our results cannot be applied to other rescuers. Second, because the results of the present study were obtained from simulation experiments using a manikin, they may not be identical to those obtained from CPR performed in humans. The dif- ferences in the environment between simulated cardiac arrest and real CPR might have affected the participants’ motivation and performance.

1. Conclusion

The vertical OHCC could provide a deeper and more adequate CCD compared with the conventional OHCC, and the advantages of the ver- tical OHCC is related to the superiority of the compression force.

Funding

This research did not receive any specific grant from funding agen- cies in the public, commercial, or not-for-profit sectors.

Authors’ contributions

OH JH contributed to the study conception and design. NOH H and LEE JG contributed to the data acquisition. NOH H, Lee JG, Kim DK, and OH JH contributed to the data analysis and interpretation. OH JH con- tributed to the drafting and critical revision of the manuscript for impor- tant intellectual content. All the authors have read and approved the final version of the manuscript.

CRediT authorship contribution statement

Je Hyeok Oh: Writing – review & editing, Writing – original draft, Vi- sualization, Validation, Supervision, Software, Resources, Project admin- istration, Methodology, Investigation, Funding acquisition, Formal analysis, Conceptualization. Hyeonseok Noh: Project administration, Methodology, Investigation, Formal analysis, Data curation. Jun Gyu Lee: Methodology, Investigation, Formal analysis, Data curation. Don- Kyu Kim: Resources, Methodology, Investigation, Formal analysis.

Declaration of Competing Interest

None.

Acknowledgements

The authors thank all participants from our hospital for their contri- butions to this study.

References

1. Van de Voorde P, Turner NM, Djakow J, de Lucas N, Martinez-Mejias A, Biarent D, et al. European resuscitation council guidelines 2021: Paediatric life support. Resus- citation. 2021;161:327-87. https://doi.org/10.1016/j.resuscitation.2021.02.015.
2. Kim MJ, Lee HS, Kim S, Park YS. Optimal chest compression technique for paediatric cardiac arrest victims. Scand J Trauma Resusc Emerg Med. 2015;23(1):36. https:// doi.org/10.1186/s13049-015-0118-y.
3. Stevenson AG, McGowan J, Evans AL, Graham CA. CPR for children: one hand or two? Resuscitation. 2005;64(2):205-8. https://doi.org/10.1016/j.resuscitation. 2004.07.012.
4. Topjian AA, Raymond TT, Atkins D, Chan M, Duff JP, Joyner Jr BL, et al. Part 4: Pedi- atric basic and advanced life support: 2020 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2020;142(16_suppl_2):S469-523. https://doi.org/10.1161/CIR.0000000000000901.
5. Lee SS, Lee SD, Oh JH. Comparison between modified and conventional one-handed chest compression techniques for child cardiopulmonary resuscitation: a randomised, non-blind, cross-over simulation trial. J Paediatr Child Health. 2019; 55(11):1361-6. https://doi.org/10.1111/jpc.14422.
6. Choi HS, Oh JH, Kim JW, Hong JY, Kim CW, Lee DH, et al. The effect of posture modification during continuous one-handed chest compression: a pilot study using in-hospital Pediatric cardiac arrest simulation. Signa Vitae. 2016;12(1):43-6.
7. Maier GW, Tyson Jr GS, Olsen CO, Kernstein KH, Davis JW, Conn EH, et al. The phys- iology of external cardiac massage: high-impulse cardiopulmonary resuscitation. Circulation. 1984;70(1):86-101. http://www.ncbi.nlm.nih.gov/pubmed/6723014.
8. Oh JH, Kim CW. Relationship between chest compression depth and novice rescuer body weight during cardiopulmonary resuscitation. Am J Emerg Med. 2016;34(12): 2411-3. https://doi.org/10.1016/j.ajem.2016.09.006.
9. Oh JH. A trade-off relationship between chest compression depth and chest wall re- coil during cardiopulmonary resuscitation. Am J Emerg Med. 2017;35(10):1572-3. https://doi.org/10.1016/j.ajem.2017.04.028.
10. Yang D, Lee W, Oh J. Effect of the use of metronome feedback on the quality of pe- diatric cardiopulmonary resuscitation. Int J Environ Res Public Health. 2021;18

(15):8087. https://doi.org/10.3390/ijerph18158087.

1. Oh JH, Lee SJ, Kim SE, Lee KJ, Choe JW, Kim CW. Effects of audio tone guidance on performance of CPR in simulated cardiac arrest with an advanced airway. Resuscita- tion. 2008;79(2):273-7. https://doi.org/10.1016/j.resuscitation.2008.06.022.
2. Sample Size Estimation. Centre for Clinical Research and Biostatistics, The Chinese University of Hong Kong. Available from: . http://www2.ccrb.cuhk.edu.hk/stat/ mean/tsmc_equality.htm [accessed 11 June 2020].
3. Roh YS, Lim EJ. Factors influencing quality of chest compression depth in nursing students. Int J Nurs Pract. 2013;19(6):591-5. https://doi.org/10.1111/ijn.12105.
4. Krikscionaitiene A, Stasaitis K, Dambrauskiene M, Dambrauskas Z, Vaitkaitiene E, Dobozinskas P, et al. Can lightweight rescuers adequately perform CPR according to 2010 resuscitation guideline requirements? Emerg Med J. 2013;30(2):159-60. https://doi.org/10.1136/emermed-2011-200634.
5. Sutton RM, French B, Niles DE, Donoghue A, Topjian AA, Nishisaki A, et al. 2010 American Heart Association recommended compression depths during pediatric in-hospital resuscitations are associated with survival. Resuscitation. 2014;85(9): 1179-84. https://doi.org/10.1016/j.resuscitation.2014.05.007.