a b s t r a c t

Introduction: Chest compressions depth and complete chest recoil are both important for high-quality Cardio- Pulmonary Resuscitation (CPR). It has been demonstrated that Anthropometric variables affect chest compres- sion depth, but there are no data about they could influence chest recoil. The aim of this study was to verify whether physical attributes influences chest recoil in lay rescuers.

Methods: We evaluated 1 minute of compression-only CPR performed by 333 laypersons immediately after a Basic Life Support and Automated external defibrillation (BLS/AED) course. The primary endpoint was to verify whether anthropometric variables influence the achievement a complete chest recoil. Secondary endpoint was to verify the influence of anthropometric variables on chest compression depth.

Results: We found a statistically significant association between weight and percentage of compressions with cor- rect release (p <= 0.001) and this association was found also for height, BMI and sex. People who are heavier, who are taller, who have a greater BMI and who are male are less likely to achieve a complete chest recoil. Regarding chest compressions depth, we confirm that the more a person weighs, the more likely the correct depth of chest compressions will be reached.

Conclusions: Anthropometric variables affect not only chest compression depth, but also complete chest recoil. CPR instructors should tailor their attention during training on different aspect of chest compression depending on the physical characteristics of the attendee.

(C) 2017

Introduction

Out of hospital cardiac arrest (OHCA) kills about 1 person per 1000 inhabitants every year and it is one of the leading causes of death in the industrialized countries [1,2]. Survival from OHCA has not signifi- cantly improved in almost 30 years and the aggregate survival rate, re- corded across various populations, is between 6.7% and 8.4% [3]. The

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

* Corresponding author at: Via S.Ennodio 10, 27100 Pavia (PV), Italy.

E-mail address: [email protected] (A. Somaschini).

¹ Joint first Authorship: contributed equally to this work.

chances of survival during an out of hospital cardiac arrest (OHCA), as stressed by ILCOR 2015 recommendations [4], strongly depend on early and high quality Cardio-pulmonary resuscitation , meaning CPR with chest compressions performed with correct depth (between 5 and 6 cm), correct rate (between 100 and 120 compressions per min- ute), correct hand position and complete chest recoil [5]. Both chest compression depth and complete chest recoil are fundamental to achieve a good quality chest compression as it has been demonstrated that both of them influence blood pressure, cardiac output, coronary perfusion pressure, and therefore, survival [6-8]. It is well known that anthropometric variables affect chest compression depth: in particular, underweight rescuers are less likely to be able to perform compressions of adequate depth [9] and, consequently, they require special attention

http://dx.doi.org/10.1016/j.ajem.2017.03.060

0735-6757/(C) 2017

E. Contri et al. / American Journal of Emergency Medicine 35 (2017) 1266-1268 1267

Table 1 Mean values (+-SD) and percentiles of the demographic characteristics of the population. Mean values (+-SD) of the chest compressions parameters: chest compression depth (Cdepth), percentage of compression with complete chest recoil (Crecoil), number of compressions per minute (Crate) and percentage of compressions with correct hand position (Cpostion).

	Weight (cm)	Height (cm)	BMI (kg/m2)	Age (years)	Cdepth (mm)	Crecoil (%)	Crate (%)	Cpostion (%)
Mean value	68 +- 14	171 +- 9	23.1 +- 3.6	35 +- 14	50 +- 7	78 +- 31	118 +- 11	94 +- 21
25th percentile	57	165	20.3	23
50th percentile	67	171	23	32
75th percentile	77	177	25.3	45

during CPR training [10]. On the other hand, there are no data on how anthropometric variables could affect chest recoil. The aim of this study was to determine whether the variables related to physical attri- butes influence chest recoil in a population of lay rescuers.

Materials and method

Study design

We performed a retrospective study of lay rescuers over 18 years of age who participated to a Basic Life Support and Automated External Defibrillation (BLS/AED) training course in the IRC-Comunita Training Centers of the nonprofit associations Pavia nel Cuore (Via de Canistris 7, Pavia, Italy) and Robbio nel Cuore (Via Mortara 5, Robbio, Pavia, Italy) between June 2014 and June 2016. It’s our practice to record, at the end of every BLS/AED course, 1 min of compression-only CPR for each participant who passes the final examination: we utilized these data for the present study. Duration of 1 min has been chosen to mini- mize the deterioration of chest Compression quality because of fatigue, according to the results from Nishiyama et al. [11].

According to results of our previous study [12], we have been using the real-time visual feedback during many of our courses, since 2015. We included only courses performed without any feedback, in order to avoid any influence of feedback on our results.

Endpoints

The primary endpoint of the study was to verify whether anthropo- metric variables influence the ability to achieve complete chest recoil. Secondary endpoint was to verify whether anthropometric variables in- fluence chest compression depth.

Course characteristics, devices and parameters

The BLS/AED course consisted of 1 h of theory and 4 h of practice with an instructor:attendees:manikin ratio of 1:5:1. The manikin used for the course was Laerdal Little Anne (Laerdal Medical, Inc., AS, Norway). At the end of the course we recorded 1 min of compression- only CPR using a Resusci Anne Wireless SkillReporter software, version

1.1.0.20 (Laerdal Medical, Inc., AS, Norway) connected to the Laerdal Resusci Anne Wireless SkillReporter manikin (Laerdal Medical, Inc., AS, Norway) for participants who passed the final examination only. We analysed, for each participant, the percentage of correctly released compressions, the percentage of compressions with correct depth (50-60 mm), the number of compressions and the percentage of com- pressions performed with correct hand position. Recorded results

were associated to a serial number, date and anthropometric variables of the provider (gender, height, weight, Body Mass Index (BMI) and age).

Statistical analysis

All data were inputted in anonymous form into a database (Microsoft Excel 2010) and then analysed with SPSS 22.0 Windows ver- sion (SPSS Inc., Armonk, NY). We stratified our population into quartiles for height, weight, BMI, age and into 2 groups based on sex. We evalu- ated differences among the quartiles by analysis of variance (ANOVA) using the Fisher’s least significant difference (LSD) correction for the post-hoc comparisons. We compared the two sex groups with Chi- square for categorical variables and Student t-test for continuous vari- ables. All categorical data are expressed in percentages, while continu- ous variables are expressed as median with their interquartile range. A p-value b 0.05 was defined as statistically significant.

Results

We enrolled 333 participants (177 male and 156 female) eligible for this study: lay rescuers, over 18 years old and participating a BLS/AED course without any feedback. Population anthropometric characteristics and values of quartiles are presented in Table 1.

Primary endpoint

Regarding our primary endpoint we found a statistically significant inverse association between weight and percentage of compressions with correct release (p <= 0.001) (Table 2). This association was found also for height, BMI and sex, while it was not significantly associated with age.

Secondary endpoint

Regarding the percentage of participants who were able to reach a mean compression depth between 5 and 6 cm, we found a statistically significant association for weight, height, BMI and sex, while it was not found for age (Table 3).

Discussion

External chest compression are the principal elements of Circulatory support during CPR [13] and chest compression depth, chest compres- sion rate and complete chest recoil play a key role to obtain high-quality chest compressions [4]. It has been widely demonstrated that

Table 2

Percentage of chest compressions performed with correct release (Median +- IQR) for the different quartiles and the different anthropometric characteristics

	1st quartile	2nd quartile	3rd quartile	4th quartile	Male	Female	p-Value
Weight	99 +- 8	97 +- 19	86 +- 60	82 +- 68			b0.001
Height	98 +- 13	97 +- 34	95 +- 31	84 +- 63			b0.001
BMI	99 +- 8	97 +- 19	85 +- 61	86 +- 48			b0.001
Age	96 +- 33	92 +- 29	96 +- 36	92 +- 48			0.820
Sex					93 +- 49	97 +- 17	0.003

1268 E. Contri et al. / American Journal of Emergency Medicine 35 (2017) 1266-1268

Table 3 Percentage of participants who performed a mean compression depth between 5 and 6 for the different quartiles and the different anthropometric characteristics

6. Conclusions

Complete chest recoil and compression depth are deeply influenced

1st quartile

2nd quartile

3rd quartile

4th

quartile Male Female p-Value

by anthropometric variables. BLS/AED instructors should tailor the course focusing their attention during training on different features of

Weight 35.0% 49.4% 69% 81% b 0.001

Height 39.5% 55.8% 65.8% 73.6% b 0.001

BMI 38.6% 58.3% 60.2% 78.3% b 0.001

Age 60.2% 55.4% 63.1% 56.6% 0.738

Sex 72.6% 42.9% b 0.001

anthropometric variables influence chest compression depth and, in particular, underweight rescuers are less likely to be able to perform chest compressions of adequate depth compared to normal weight or overweight rescuers [9,10]. Conversely there are no data on how an- thropometric variables could influence chest recoil. Our study demon- strated that chest recoil depends on the physical characteristics of the rescuer: people who are heavier, who are taller and who have a greater BMI are less likely to achieve a complete chest recoil. Consistently, male subject achieve complete chest recoil less than female subject. Regard- ing chest compressions depth, we confirm that the more a person weighs, the more likely the person is able to reach the correct depth of chest compressions. Moreover people who are taller, who have a great- er BMI and male subjects are more likely to achieve a compression depth between 5 and 6 cm. Age, in our population, did not affect either chest recoil or chest compression quality, suggesting that probably only physical characteristics influence the performance, regardless of age. In conclusion, we have demonstrated that anthropometric variables are important not only to achieve the correct compression depth, but also to obtain a complete chest recoil. This evidence is really valuable for CPR instructors who should tailor the teaching, focusing their attention on different features of chest compressions depending on the subject they are teaching to: for people who are high, heavy and males they should focus on achieving the complete chest recoil, whilst for people who are lightweight, short and females they should focus on achieving the correct compression depth.

5. Limitations

The manikin used for the course was Laerdal Little Anne (Laerdal Medical, Inc., AS, Norway), whilst the single minute of compression- only CPR was performed on a slightly different manikin, a Laerdal Resusci Anne Wireless SkillReporter manikin (Laerdal Medical, Inc., AS, Norway). We think that this little difference could not affect our re- sults because all the people use the two manikins in the same way and for the same time and, moreover, the manikin are very similar and, ac- cording to manufacturer specifications, it’s necessary the same force to achieve the same compression depth.

Another limitation is that it is a retrospective study. Nevertheless, all the courses were performed using the same methodology (i.e., same slides, same syllabus), in the same place (i.e., the headquarters of the two associations), at the same time of the day (weekend mornings) and by the same pool of instructors.

chest compressions depending on the physical characteristics of the attendee.

Disclosure

The authors report no conflicts of interest.

Acknowledgments

We would like to thank all of the volunteers of the nonprofit associ- ations Pavia nel Cuore and Robbio nel Cuore for their irreplaceable work in organizing BLS/AED courses for free. We offer a special thanks to Dr. Dario Fina, Dr. Beatrice Zelaschi and Dr. Marzia Di Maggio for their help in data collection.

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