Article, Emergency Medicine

Comparison of chest compression kinematics associated with over-the-head and standard cardiopulmonary resuscitation

Brief Report

Comparison of chest compression kinematics associated with over-the-head and standard cardiopulmonary resuscitation?

Chih-Hsien Chi MD a, Jui-Yi Tsou b c, Fong-Chin Su PhD b,?

aDepartment of Emergency Medicine, National Cheng Kung University, Tainan, Taiwan bInstitute of Biomedical Engineering, National Cheng Kung University, Tainan, Taiwan cDepartment of Physical therapy, Fooyin University, Kaohsiung, Taiwan

Received 23 July 2008; revised 29 August 2008; accepted 29 August 2008

Abstract

Background: Over-the-head cardiopulmonary resuscitation (CPR) is a method of chest compression, which may be easier to perform than standard CPR in a confined space.

Purpose: The purpose of this study was to evaluate the effects of over-the-head CPR on the kinematics and the force of delivered compressions.

Methods: The subjects were 21 health care providers who were experienced in CPR. Each participant performed over-the-head CPR (O) and standard CPR (S). The compression-to-ventilation ratio was 30:2. The CPR duration was 2 minutes in each position, with a rest period of 15 minutes between each instance. The order in which positions were adopted was randomized. A manikin was equipped with a 6-axial force load cell to collect 3-dimensional compression forces at a sampling rate of 1000 Hz. An 8-camera digital motion analysis system was used to collect 3-dimensional trajectory information. Data were compared by Crossover design analysis of variance (P b .05 represents statistical significance).

Results: No significant differences in range of motion of the head, shoulder, lower trunk, hip, and knee were obtained using the 2 methods. The compression forces in O and S were 386.64 +- 47.32 and 397.35 +-

41.89 N, respectively (P N .05). No significant differences between the compression frequencies, depths, and percentages correct were obtained using the 2 methods.

Conclusions: There were no differences between the kinematics, compression forces, depths, and frequencies obtained using the O and S CPR methods as practiced by experienced providers.

(C) 2009

Introduction

? The authors would like to thank National Science Council of the Republic of China, Taiwan, for financially supporting this research under contract no. NSC 94-2320-B-006-041.

* Corresponding author. Tel.: +886 6 2760665; fax: +886 6 2343270.

E-mail address: [email protected] (F.-C. Su).

early cardiopulmonary resuscitation (CPR) is an impor- tant action in the Chain of survival for cardiac arrest [1-3]. However, a normal cardiac output could not be obtained even when chest compression is correctively and optimally performed [4]. This condition is worsened when the CPR

0735-6757/$ – see front matter (C) 2009 doi:10.1016/j.ajem.2008.08.029

is implemented or performed in a confined space, for example, in the ambulance.

There has been little prior work on the effects of rescuers of performing CPR in a confined space. Recently, an alternative method called over-the-head CPR has been developed for such conditions [5]. Unlike in standard CPR, in which the rescuers must place a knee above and beside the head of the victim to perform ventilation and chest compression, in this approach, the CPR provider need not move their body during alternate chest compression and ventilation. Investigations have demonstrated that the efficiency of over-the-head CPR is as good as or even better than that of standard CPR [5-8].

Most research on CPR techniques discusses the effects of motion (performance outcome), compression depth, com- pression rate, and cyclic time [9,10]. However, the position of the rescuer may affect the muscle recruitment and therefore the performance of CPR [11]. The hypothesis of this study is that the effect that positioning might have on standard vs over-the-head CPR, that is, the position affects the kinematics (angle of motion) and kinetics (forces delivered, depth, and frequency) during CPR. This work thus explores the effect of motion on the performance of chest compression. The goal of this work was to compare over-the-head CPR with standard CPR to investigate the kinematics and kinetic factors of the over-the-head CPR on manikin model.

Materials and methods

Study design

This experiment was performed using a crossover design. It was approved by the Human Ethics Committee of the National Cheng Kung University Hospital (Tainan, Taiwan). All subjects provided informed and written consent.

Twenty-one emergency medical professionals, compris- ing 15 male emergency medical technician firefighters and 6 female emergency department registered nurses from a university medical center, participated voluntarily. All subjects were experienced in prehospital or in-hospital standard CPR. The approach follows that demonstrated by our group earlier [11].

Study protocol

The participants had no muscular skeletal injury, sprain, or pain. No food was eaten 30 minutes before the tests. The ingestion of alcohol, tea, and coffee was prohibited on the day of each test. The study was performed at the motion analysis laboratory of the Department of Medical Engineer- ing. The participants, who were all experienced emergency health care providers, reviewed both methods on manikins before they began the tests.

Each participant then performed CPR in 2 positions– standard CPR while kneeling beside the Resusci Anne

manikin (Laerdal Medical, Wappingers Falls, NY) placed on the floor and over-the-head CPR on the floor. The compression-to-ventilation ratio was 30:2 simulating 2 person CPR following 2005 Basic Life Support (BLS) guidelines [12]. The External Cardiac Compression (ECC) duration was 2 minutes in each position, alternating with rest periods of 15 minutes. The order of the adopted positions was randomized. To maintain the compression rate for more than 100/min, a metronome was used as the audio prompt in every ECC position. Other compression variables were recorded by using the Laerdal Resusci Annie manikin. Participants were blind to the values of the parameters in the study.

Motion analysis

Three-dimensional motion analysis was performed to define and compare the motions of the joint angles. An image-based motion analysis system was adopted with markers’ reflecting light back to sensors. A similar 3- dimensional motion analysis was used to define patterns of joint motion in a study of various Musculoskeletal problems, which are generally linked to repetitive motion.

To record the movements, a set of reflective markers were placed on selected anatomical landmarks on the surface of the body of each subject. Thirty-seven passively reflective markers were placed on selected anatomical landmarks on the right upper extremity, head, trunk, and bilateral lower extremity of each subject to determine the embedded axes of segments. The linkage diagram of reflective markers for motion analysis was shown in Fig. 1. In addition, three marks were placed on the load cell to define the coordinate system of the cell. A video-based motion system with 8 Motion Analysis HiRes cameras (Motion Analysis Corp, Santa Rosa, Calif) recorded the marker motion, with high- resolution and complex motion capturing. The presented data show both the compression and the decompression phases, and the results represent the mean average angle measured during a period of 20 seconds. The light-reflective marker positions in 3-dimensional space were captured and quantified using a charge-coupled device and Motion Analysis EVA software (Motion Analysis Corp, Santa Rosa, Calif). The operating software of the system gathers the 2-dimensional camera images and processes the data to 2- dimensional or 3-dimensional assessments [11].

Delivery of compression forces

The manikin was equipped with a 6-axial force transducer (AMTI MC3A-6-1000, Advanced Mechanical Technology Inc, Watertown, Mass) to measure 3-dimensional compres- sion forces at a sampling rate of 1000 Hz. This transducer was fixed to the sternum of the manikin. The transducer was

7.62 cm (3 in) high, so the rescuers were placed 7.62 cm (3 in) above the floor of the laboratory on a flat wood box to reach a similar height to that of ordinary manikin operation.

Fig. 1 Linkage diagram of reflective markers for motion analysis. A, lateral view; B, front view; and C, oblique view.

Data analysis

The data on joint angles and compression forces were obtained during the middle cycles of the CPR session. Suppose a difference of 5% in percent change of compres- sion force is considered of Clinically meaningful difference. By using crossover design, assuming that the SD is 10%, the

required sample size to achieve an 80% power at ? = .05 for correctly detecting such difference is more than 16. The means and SDs of the demographic and outcome variables were obtained and presented. Data were analyzed using SPSS version 13 (SPSS, Chicago, Ill). Statistical significance was set at P b .05 throughout the experiment. Descriptive statistics were obtained, and a paired t test was conducted to

Fig. 2 Cyclic dynamic changes in joint angles during chest compression. No difference existed between cyclic movement patterns of over- the-head and standard groups.

Table 1 Range of motion (joint angles, in degree) associated with various positions (over-the-head and standard)

Joint

Movement

Over-the-head

Mean +- SD

Standard

Mean +- SD

Mean difference

95% confidence interval

Upper Lower

P

Head

Flexion-extension

5.60 +- 3.17

5.53 +- 3.30

0.06

-0.54 0.67

.83

Upper trunk

Flexion-extension

2.05 +- 0.88

2.00 +- 0.87

0.05

-0.24 0.34

.73

Abduction-adduction

0.86 +- 0.46

0.94 +- 0.73

-0.07

-0.35 0.21

.59

Rotation

0.85 +- 0.35

0.7 +- 0.22

0.15

0.01 0.28

.03 ?

Lower trunk

Flexion-extension

1.83 +- 1.58

1.96 +- 1.73

-0.14

-0.46 0.18

.39

Abduction-adduction

0.67 +- 0.29

0.73 +- 0.27

-0.06

-0.20 0.09

.42

Rotation

0.49 +- 0.24

0.53 +- 0.24

-0.04

-0.15 0.06

.42

Shoulder

Flexion-extension

3.18 +- 1.20

3.03 +- 1.03

0.15

-0.32 0.63

.50

Abduction-adduction

2.66 +- 1.41

2.72 +- 1.62

-0.06

-0.57 0.44

.80

Rotation

2.12 +- 1.13

2.08 +- 1.71

0.04

-0.50 0.58

.88

Elbow

Flexion-extension

6.16 +- 3.89

5.93 +- 3.67

0.23

-0.61 1.07

.58

Wrist

Flexion-extension

4.65 +- 2.27

4.66 +- 2.84

-0.02

-0.91 0.88

.97

Hip

Flexion-extension

12.28 +- 3.62

12.31 +- 3.60

-0.03

-0.69 0.64

.94

Abduction-adduction

1.03 +- 0.69

0.93 +- 0.50

0.10

-0.17 0.36

.46

Rotation

4.48 +- 2.51

4.22 +- 2.28

0.26

-0.44 0.96

.45

Knee

Flexion-extension

3.72 +- 1.80

4.20 +- 1.76

-0.48

-0.95 0.00

.05

Ankle

Flexion-extension

3.76 +- 3.42

2.94 +- 2.74

0.81

0.01 0.61

.05

* P b .05 as significant.

study the difference between the joint angles and the compression forces obtained using the 2 methods. The effect was significant as P b .05.

Results

The mean age of the participants was 28.5 +- 4.1 years old, their mean height was 168.6 +- 6.9 cm, and their weight was

68.0 +- 10.5 kg. Fig. 2 indicates that the cyclic dynamic change of the joint angles during chest compression was similar. No difference existed between the cyclic motion patterns of the over-the-head and standard group. Almost all range of motion (joint angles, in degree) associated with various positions indicated no significant change in angles during the middle cycle of the CPR session (Table 1). The only significant difference was between the angles of the upper trunk in over-the-head and standard groups (0.85 +- 0.35 vs 0.70 +- 0.22; P = .03). The mean compression force

(Newton) of the over-the-head and standard groups were

386.64 +- 47.32 and 397.35 +- 41.89, respectively (P N .05). Table 2 presents the performance outcome associated with various positions. The average compression depth, average compression rate, and percentage correct (%) compression did not differ significantly between the over-the-head and standard groups.

Discussion

The principal finding in this study is that rescuers performing chest compressions on a manikin deliver similar forces, kinematics, and performance whether they use the standard or over-the-head technique.

A previous study by Handley [5] demonstrated that the mean compression depth was significantly less, more compressions of incorrect depth occurred, and poor Hand placement was more likely when the over-the-head method

Table 2 Performance outcome in various positions (over-the-head and standard)

Performance outcome

Over-the-head

Standard

Mean

95% confidence

P

difference

interval

Mean +- SD

Mean +- SD

Upper Lower

Average compression rate (time/min)

111.14 +- 16.60

110.23 +- 15.26

0.90

-3.11 4.92

.64

Average depth (mm)

47.14 +- 3.07

47.47 +- 3.50

-0.33

-1.87 1.20

.65

Average number per min

112.80 +- 20.79

109.76 +- 15.75

3.04

-1.59 7.69

.18

Percentage correct (%)

64.61 +- 34.95

59.71 +- 40.30

4.90

-5.92 15.73

.35

Too deep

5.19 +- 8.14

7.66 +- 10.75

-2.47

-5.84 0.89

.14

Too shallow

0.76 +- 0.80

0.83 +- 1.07

-0.04

-0.55 0.46

.84

was used. The authors suggested that additional training may be required before the technique can be safely implemented. Our work compares these 2 methods by kinematic measure- ment and of manikin output. The only difference between the over-the-head and standard methods was in the upper trunk rotation angle. However, this measured difference between angles was less than 1? and may not be clinically significant. The reason for this variation is that during standard CPR, even in 2-person resuscitation, the rescuer turns toward the head of the victim to evaluate him or her, which may explain the larger angular change in the standard position.

The percentages of correct compressions obtained using these 2 methods were similar. The results and data herein were similar to those of earlier studies in both positions, perhaps indicating that over-the-head CPR is of a similar quality to standard position CPR [13-16]. The compression force delivered and other parameters support this assertion. The motion analysis system here was used to define patterns of joint movement of various musculoskeletal problems, usually related to repetitive motion [13]. This study differed from previous over-the-head CPR studies in setting out to compare angles of joint motion and compres- sion force between the 2 techniques. The rationale for measuring these parameters is based on the cyclical move- ment of CPR that results in repetitive thoracolumbar excursion [17-19]. The clinical relevance for measuring

these parameters warrants further investigations.

This study has limitations. First, the ventilation variables in over-the-head and standard CPRs were not evaluated. Second, the hand-off times were not studied because of limitations of the equipment software. Third, the participants were clinical experts in chest compression in a simulation environment; the effect of kinematics variables associated with bystander-level rescuers using the over-the-head technique on a manikin model is unknown.

In this study, we have identified several previous studies that have compared standard to over-the-head CPR and on the whole found them to be equivalent in compression efficacy. No differences existed between the kinematics, compression forces, depths, and frequencies obtained using over-the-head and standard CPR methods as performed experienced providers.

Acknowledgment

Ted Knoy is appreciated for his editorial assistance.

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