a b s t r a c t

Purpose: To improve the quality of chest compression , we developed the assistant-push method, whereby the second rescuer pushes the back of the chest compressor during CC. We investigated the effectiveness and feasibility of assistant push in achieving and maintaining the CC quality.

Methods: This was a randomized crossover trial in which 41 subjects randomly performed both of standard CC (single-rescuer group) and CC with instructor-driven assistant push (assistant-push group) in different order. Each session of CC was performed for 2 minutes using a manikin. Subjects were also assigned to both roles of chest compressor and assistant and together performed CC with subject-driven assistant push. depth of CC, compression to recoil ratio, duty cycle, and rate of incomplete recoil were quantified.

Results: The mean depth of CC (57.0 [56.0-59.0] vs 55.0 [49.5-57.5], P b .001) was significantly deeper, and the compression force (33.8 [29.3-36.4] vs 23.3 [20.4-25.3], P b .001) was stronger in the assistant-push group. The ratio of compression to recoil, duty cycle, and rate of incomplete chest recoil were comparable between the 2 groups. The CC depth in the single-rescuer group decreased significantly every 30 seconds, whereas in the assistant-push group, it was comparable at 60- and 90-second time points (P = .004). The subject assistant- push group performed CCs at a depth comparable with that of the instructor assistant-push group.

Conclusion: The assistant-push method improved the depth of CC and attenuated its decline, eventually helping maintain adequate CC depth over time. Subjects were able to feasibly learn assistant push and performed effectively.

(C) 2014

Introduction

Adequate chest compression is a crucial determinant of successful outcomes over the restoration of spontaneous circulation (ROSC) in cardiac arrest victims because the perfusion during cardiopul- monary resuscitation (CPR) depends on CC [1,2]. Therefore, guidelines have placed more emphasis on the importance of CC during CPR, the current recommendation being to push the chest to a depth of at least 5 cm [3,4]. However, many trained health care providers still perform inadequate depth of CC regardless of in-hospital or out-of-hospital settings [5,6].

? Funding sources/disclosures: This work was supported by a grant (CRI 14019-1) from Chonnam National University Hospital Research Institute of Clinical Medicine, Gwangju, Republic of Korea.

?? This work was supported by a grant (CRI 14019-1) from OO Research Institute of

Clinical Medicine, Chonnam, National University Hospital.

* Corresponding author. Tel.: +82 62 220 6809; fax: +82 62 228 7417.

E-mail address: [email protected] (B.K. Lee).

Several studies investigated the factors affecting the quality of CC [7-13]. Women, children, and lightweight rescuers often have difficulty producing enough physical strength to push the chest to the recom- mended depth. Moreover, the act of CC can easily cause physical fatigue in these rescuers, which results in a rapid decline in CC quality [7-13]. Hasegawa et al [7] suggested that lightweight rescuers should rotate at 1-minute intervals to maintain high quality of CC. In another study, Krikscionaitiene et al [14] reported that a 5-second intervention in which the instructor pushed on the trainee’s shoulders improved the quality of CC during training exercises. Whether special attention is given during training or intervention is performed, there are still limita- tions to achieving and maintaining adequate quality of CC because sex, age, and physical fitness factors (such as weight and height) are fixed. We developed a method similar to that of Krikscionaitiene et al [14] who reported to improve the quality of CC. The approach requires that the second rescuer simultaneously pushes on the back of the first rescuer, who performs CC. We investigated the feasibility of this method and hypothesized that it would be effective in achieving and maintain- ing CC quality, especially among rescuers for whom achieving adequate

CC depth may prove challenging.

http://dx.doi.org/10.1016/j.ajem.2014.12.005

0735-6757/(C) 2014

Methods

Participants

We recruited 41 college students majoring in emergency Medical technology to participate in this study. A minimum sample size of 16 is required for an effect size of 0.89 and statistical power of 90%; these parameters are necessary to detect a 5% difference in preliminary data. Ethical approval was obtained from the institutional review board (CNUH-2014-052). Written informed consent was obtained from all subjects.

Study design and protocol

This was a randomized crossover trial. Subjects were assigned to 2 groups and performed 2 methods of CC on a Resusci Anne (Laerdal, Stavanger, Norway) manikin placed on the floor in different order: standard continuous single-rescuer CC (single-rescuer group) and continuous CC with assistant push (assis- tant-push group). The assistant-push method was performed by an in- structor with basic life support (BLS) certification from the American Heart Association. In this approach, the instructor pushed the subject’s upper back with 1 hand, while they performed CC (Fig. 1). Each CC method was performed without ventilation for 2 minutes using a met- ronome at a rate of 110 min^-1. No visual or acoustic feedback was per- mitted during CC. Each CC method was performed on a load cell (CAS Korea, Seoul, South Korea) to obtain and compare the compression force [15].

After the completion of both methods of CC, the assistant-push method was introduced to the subjects, at which point they were assigned to both roles of chest compressor and assistant. The randomly assigned 41 pairs of subjects performed CC with assistant push without instructor assistance for 2 minutes to identify the feasibility of assistant push during CC.

Data collection

The data for demographics of all participants were obtained, includ- ing age, sex, weight, height, body mass index (BMI), frequency of BLS training, and time since most recent BLS education. Chest compression performance data were collected using the Laerdal SkillReporter (Laerdal), including compression rate, depth of CC, correct depth of CC, ratio of compression to recoil, duty cycle, and incomplete recoil rate. Per- formance of CC on a load cell was recorded to obtain the compression force for every CC. Mean depth of CC by a single rescuer was dichoto- mized; mean compression depth greater than or equal to 50 mm was de- fined as “correct” and mean compression depth less than 50 mm defined as “incorrect” [4]. Difference in mean CC depth was calculated as the difference between mean depth of CC by assistant push and by a single rescuer. Rate of CC depth difference was also calculated as the difference in mean CC depth divided by mean CC depth by a single rescuer.

Data analysis

The categorical variables were expressed as numbers (%). The continuous variables were expressed as means +- SD or medians (inter- quartile range) as a result of the normality test. The paired comparison of continuous variables was performed with the paired t test or Wilcoxon Signed Rank Test as appropriate. The comparison of continu- ous variables between independent groups was performed using the independent t test or Mann-Whitney U test as appropriate. The effect of assistant-push CC over time was assessed using repeated-measures analysis of variance, where the response variables were set as mean CC depth and mean CC depth difference at 30-second intervals. Post hoc analysis at each time point (25-30, 55-60, 85-90, and 115-120 sec- onds) was performed using the paired t test with the Bonferroni correc- tion. The association between continuous variables was evaluated by spearman correlation coefficient. Multivariate forward stepwise linear regression was used to identify variables affecting the depth of CC.

Fig. 1. Assistant-push method. While the primary chest compressor is performing CCs, the second rescuer simultaneously pushes on the primary chest compressor’s upper back with 1 hand.

Compression quality“>chest compression quality according”>Table 1

Comparison of CC quality between the single-rescuer and assistant-push methods

Effect of fatigue on CC depth

Single rescuer (n = 41)

Assistant push P

(n = 41)

The depth of CC decreased over time in both single-rescuer and assistant-push groups (P b .001). However, repeated-measures analysis

CC rate, min^-1 110 (109-110) 110 (109-112) .020

Correct depth of CC, % 98.0 (50.5-100.0) 99.0 (98.0-100.0) b.001

Mean depth, mm 55.0 (49.5-57.5) 57.0 (56.0-59.0) b .001

Compression to recoil ratio 0.80 (0.75-0.91) 0.83 (0.75-0.88) .328

Duty cycle, % 44.7 +- 4.9 44.5 +- 3.6 .743

Incomplete recoil, % 0.0 (0.0-0.0) 0.0 (0.0-0.0) .173

Compression force, kg 23.3 (20.4-25.3) 33.8 (29.3-36.4) b.001 Data are expressed as median with interquartile range or mean +- SD.

Data were analyzed using PASW/SPSS version 18.0 for Windows (IBM, Chicago, IL). A P value b .05 was considered significant.

Results

All 41 subjects (29 men and 12 women) were included in the study. The median age of the participants was 23 years (21-24 years). The medi- an weight was 65 kg (range, 58-73 kg), and the mean height was 171.8 +-

8.2 cm. The median BMI was 22.2 kg/m^-2 (20.5-23.8 kg/m^-2). The medi- an frequency of BLS training sessions was 3 (2-3), and the median time interval from the last BLS training was 6 months (1-12 months).

Chest compression quality

The assistant-push group had a higher CC rate than the single- rescuer group (P = .020). The mean depth of CC, correct depth of CC rate, and compression force were significantly greater in the assistant- push group than in the single-rescuer group (Table 1). The ratio of com- pression to recoil, duty cycle, and rate of incomplete chest recoil were comparable between the 2 groups (Table 1). The incorrect depth of CC group showed significant improvement in CC depth and higher rate of CC depth difference (Table 2). Subjects in the incorrect CC depth group also displayed a significantly shorter stature than those in the correct CC depth group (167.4 +- 8.6 cm vs 173.3 +- 7.7 cm, P = .049). Age, sex, weight, and BMI were comparable between both incorrect and correct depth of CC groups.

Correlation with depth of CC

The correlation analysis and Multivariate linear regression were per- formed for a total of 82 sessions of CC. The highest correlation was found between body weight and depth of CC (r = 0.408, P b .001). Age and height also had significant correlation with depth of CC (r = 0.313, P = .004 and r = 0.363, P = .001, respectively). Female subjects per- formed CC at a significantly shallower median depth than male subjects (53.5 mm [49.0-57.0] vs 57.0 mm [55.0-59.0], P = .002). Body mass

index does not significantly correlate with depth of CC (r = 0.130, P = .244). Weight, height, age, sex, and assistant-push characteristics were included in the regression model. Height (B = 0.291, SE = 0.066, P b .001) and assistant push (B = 4.366, SE = 1.077, P b .001) remained significant in the final multivariate linear regression model (R² = 31.2, P b .001).

of variance showed significant interaction between time and the 2 groups (P = .004) (Fig. 2). The depth of CC at 30-second intervals within 2 minutes was decreased significantly in the single-rescuer group, whereas the depths of CC at 60 and 90 seconds were comparable in the assistant-push group (Fig. 2). The difference in mean CC depth increased over time (P b .001; Fig. 2).

Chest compression quality according to sex

A higher CC rate was observed in the male assistant-push group than in the male single-rescuer group (P = .024), whereas the corresponding female groups showed no difference. The assistant-push method was associated with a higher mean depth of CC, correct depth of CC rate, and compression force in both Males and females (Table 3). The improvement in mean depth of CC and correct depth of CC rate was robust in the female group (Table 3).

Feasibility of assistant-push method

The subject assistant-push group performed depths of CC compara- ble with the instructor assistant-push group (Table 4). The ratio of com- pression to recoil, duty cycle, and rate of incomplete chest recoil were also comparable between these 2 groups (Table 4).

Discussion

The CCs coupled with assistant push improved the depth and the rate of correct depth of CC without increasing incomplete chest recoil, unlike with standard single-rescuer-administered CCs. The increase in mean CC depth was prominent in the incorrect depth of CC group; however, assistant push attenuated the decline in CC capacity over time. One of the benefits of the assistant-push CC method is that it can be performed feasibly and is an effective way to improve upon the classic technique, as we have shown. This clearly fills a niche, as studies show that even health care providers face challenges, when performing ade- quate CPR [5,6]. Depth of CC was 35 +- 10 mm during the first 5 minutes of out-of-hospital CPR, and shallow depth (b 38 mm) of CC was 37.4% during the first 5 minutes of In-hospital CPR (in accordance with CPR guidelines at the time of study) [5,6]. There was a high proportion of study participants who performed CCs with an incorrect mean depth (24.4%, 10/41 subjects) in our study, despite all participants being

students majoring in emergency medical technology.

Weight, height, sex, and age are well-known factors influencing depth of CC, and although they may exhibit individual effects, they are interdependent [7-13]. Subjects who were older, taller, heavier, and of the male sex achieved more adequate depth of CC in a study conducted on schoolchildren [8]. Those who were younger, shorter, lighter, and of the female sex generally displayed a correlation with poor CC perfor- mance; these rescuers would not produce CCs meeting the current guidelines [7-13]. Our correlation analysis showed that weight, height, and age have significant correlation with depth of CC. Being of the male sex is also associated with higher depth of CC. Age, sex, and anthropometric data such as height and weight cannot be readily or easily changed in the short term. Therefore, several researchers

Table 2

Comparison of changes in CC depth between the correct depth group and incorrect depth group

	Correct depth (n = 31)	Incorrect depth (n = 10)	P
Difference in mean CC depth, mm	1.9 +- 2.5	12.0 +- 4.0	b.001
Rate of CC depth difference	0.04 +- 0.05	0.30 +- 0.12	b.001
Data are expressed as mean +- SD.

Fig. 2. Time lapse of the change in CC depth. A, The depth of CC decreased over time in both groups (P b .001). However, the change in CC depth over time was different between the 2 groups (P = .004). The depth of CC decreased significantly at every 30 seconds in the single-rescuer group, whereas the depths of CC at 60 and 90 seconds in the assistant-push group

were comparable. B. The difference in mean CC depth between the single-rescuer group and the assistant-push group increased over time (P b .001). The differences in CC at 90 and 120 seconds were significantly higher than at 30 seconds. ?P b .05 (Bonferroni-adjusted value).

suggested providing special attention during CPR training, a fitness program, 1-minute rotations of CC, or instructor intervention to the rescuers expected to perform inadequate CC [7,9,11,12,14]. Krikscionaitiene et al [14] demonstrated that the training method of pushing on the trainee’s shoulders while performing CC increased the CC depth achieved among female rescuers. They also suggested that further research should be undertaken concerning the effect of a second pair of hands being placed on the shoulders of the primary rescuer [14]. We found the assistant push during CC execution to be similar to the method suggested by Krikscionaitiene et al [14] as an effective method of improving CC quality.

After controlling for confounding factors, the assistant push still remains a significant factor, having improved the depth of CC by

4.366 mm. The consequences of improving CC depth are evident; Edelson et al [16] demonstrated that an increase in depth of CC is associated with increased chance of hospital admissions with ROSC (5% increase per 1 mm), and Kramer-Johansen et al. [17] demonstrated that a 5-mm increase in depth of CC is associated with approximately a 2-fold increase in the odds of successful defibrillation. According to the previous studies, the assistant-push method could increase hospital admission with ROSC by approximately 20% and provide approximately 2-fold increase in the odds of successful defibrillation. Subjects who did not achieve the adequate CC depth by single-rescuer CC in the present study have the potential to improve hospital admission with ROSC by approximately 60% and increase the odds of successful defibrillation by approximately 4-fold. The assistant push slightly increased the CC rate in the present study. An increase in CC rate toward 125 min^-1 was previously associated with better resuscitability [18]. Notably, the assistant-push method would be especially helpful to rescuers with poor physical fitness. It is evident that rescuers of short stature can improve the depth of CC with the assistant-push method because the incorrect CC depth subjects were short of stature, and height remained a significant factor associated with CC depth even after controlling for confounding factors. The improvement in the correct depth of CC

and mean depth of CC was also prominent in female rescuers in the present study.

The level of CC quality declines over time due to rescuer fatigue [19-21]. Hightower et al [19] reported that the compression adequacy declined over time, dropping drastically from 93% of CCs during the first minute to 67% during the second minute. McDonald et al [20] also identified that the quality of CC fell most rapidly within the first 2 minutes and continued to decrease gradually over time during 5 mi- nutes of CPR. Our work indicates that the depth of CC decreased signif- icantly during 2 minutes of compressions administered by subjects in both the single-rescuer and assistant-push groups. However, the assistant-push method attenuated the decline of CC depth and eventu- ally helped maintain more adequate depth of CC over time than the single-rescuer CC approach. The significant difference in depth of CC at 90 and 120 seconds compared with 30 seconds supports the view that assistant push is more effective at improving depth of CC to sustain CC quality throughout 2 minutes of rescue, rather than at the beginning of CPR.

Cardiopulmonary resuscitation education is one of the key issues we can undertake to improve outcomes in cardiac arrest victims. To ensure acquisition and retention of resuscitation knowledge and skills, a sim- plified education-based approach is suggested [22]. The CPR skill should be simple and easy to learn. The participants in the present study were briefly introduced to the assistant-push method after finishing 2 sessions of CC and were able to indirectly experience this approach, if only for the 2 minutes that they were performing CC. In spite of the brief education of assistant push, participants performed the method by themselves with a quality comparable with that of a trained instructor. Therefore, knowledge of the assistant-push technique could be easily disseminated to a wide demographic.

The assistant-push method requires 2 rescuers. The synchrony between the primary compressor and the assistant is essential, when performing assistant-push CC, as any dyssynchrony can inhibit chest recoil. Incomplete chest recoil is known to be associated with decreased

Table 3

Comparison of CC quality between the single-rescuer and assistant-push methods according to sex

	Male single rescuer (n = 29)	Male assistant push (n = 29)	P	Female single rescuer (n = 12)	Female assistant push (n = 12)	P
CC rate, min-1	110 (109-110)	110 (109-112)	.024	110 (107-110)	111 (107-113)	.365
Correct depth of CC, %	99.0 (82.5-100)	99.0 (99.0-100)	.017	63.5 (2.8-96.0)	98.5 (81.7-99.8)	.003
Mean depth, mm	56.0 (52.5-59.0)	58.0 (56.5-60.0)	.001	50.0 (39.0-54.5)	57.0 (52.5-58.0)	.002
Compression to recoil ratio	0.83 +- 0.11	0.83 +- 0.08	.799	0.77 (0.71-0.95)	0.80 (0.69-0.85)	.264
Duty cycle, %	45.0 +- 4.7	45.2 +- 3.1	.803	43.9 +- 5.3	42.7 +- 4.2	.275
Incomplete recoil, %	0.0 (0.0-0.0)	0.0 (0.0-0.0)	.173	(0.0-0.0)	0.0 (0.0-0.0)	1.000
Compression force, kg	23.8 (21.8-26.1)	35.2 (33.6-36.6)	b.001	18.4 (17.0-19.8)	25.2 (22.4-29.3)	.002

Data are expressed as median with interquartile range or mean +- SD.

Table 4

Comparison of CC quality of the assistant-push maneuver: instructor performed vs subject performed

	Instructor assistant push (n = 41)	Subject assistant push (n = 41)	P
CC rate, min-1	110 (109-112)	110 (107-111)	.083
Correct depth of CC, %	99.0 (98.0-100.0)	99.0 (82.5-100.0)	.353
Mean depth, mm	57.0 (56.0-59.0)	57.0 (54.0-60.0)	.301
Compression to recoil ratio	0.83 (0.75-0.88)	0.80 (0.74-0.88)	.734
Duty cycle, %	44.5 +- 3.6	44.7 +- 4.3	.513
Incomplete recoil, %	0.0 (0.0-0.0)	0.0 (0.0-0.0)	.373

Data are expressed as median with interquartile range or mean +- SD.

cardiac index, coronary perfusion pressure, and cerebral perfusion pres- sure [23]. However, use of assistant push did not increase the rate of in- complete chest recoil, regardless of whether method was performed by study participants or a trained instructor. The dyssynchrony also could increase the duty cycle. Animal studies have shown that 30% of com- pression duty cycle provides superior Coronary and cerebral perfusion compared with 60% of duty cycle [24,25]. Under the consideration of practical and educational feasibility, guidelines suggest the optimal level to be a 50% of duty cycle [2]. It should be noted that, in the present study, the duty cycle was also unaffected by the assistant-push method. Our study was performed using a metronome to identify the effective- ness of assistant push in CC depth without confounding effects such as compression rate. However, it is possible that the metronome may aid in keeping the primary compressor and assistant in synchrony, eventu- ally preventing adverse events such as incomplete chest recoil and increase in duty cycle.

Our study has several limitations, the first of which is that this was a simulation study performed on manikins under a controlled experi- mental setting; our results may be different in authentic cardiac arrest victims. Moreover, Hands-only CPR was performed in the present study, and guidelines encourage this hands-only CPR technique for the untrained lay rescuer [2]. Therefore, assistant push can only be applied to hands-only CPR. Despite this fact, assistant push can be also applied to continuous CCs of intubated cardiac arrest victims. Further study is required concerning the effect of assistant push on the standard prac- tices of CPR, including ventilation. One other limitation is that the assistant-push method requires 2 rescuers. Two rescuers can perform CPR by switching the primary compressor every 2 minutes; however, we did not investigate the effect of assistant push on switching rescuing compressor because CC was performed for only 2 minutes in the present study. Thus, it would be beneficial to evaluate the effectiveness of assistant push in the context of prolonged resuscitation. In addition, all participants were young students majoring in emergency medical technology. It is possible that they had encountered or learned CPR previously, through their schooling. They were able to perform CPR relatively well, and it was feasible for them to understand and learn the assistant-push method. However, this approach was invented for the poor performer of CC, and realistically, the assistant-push method should be conducted on poor CC performers such as schoolchildren and those subjects of short stature and light weight.

Conclusions

The assistant-push method improved the depth of CC and is more effective in improvement of CC adequacy to the poor CC performer. The assistant-push approach helped maintain CC quality over a period of 2 minutes, and its efficacy in improving CC depth became prominent over time. Subjects were able to feasibly learn the assistant push and

performed effectively. We suggest that the assistant-push method could be taught to members of the population for whom performing CCs may prove challenging.

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