chest compression rate may be n”>American Journal of Emergency Medicine (2012) 30, 226-230

Brief Report

A higher chest compression rate may be necessary for metronome-guided cardiopulmonary resuscitation

Tae Nyoung Chung MD ^a,b,?, Sun Wook Kim MD ^a, Je Sung You MD ^a,

Young Soon Cho MD ^c, Sung Phil Chung MD, PhD ^a, Incheol Park MD, PhD ^a

^aDepartment of Emergency Medicine, Yonsei University College of Medicine, Seodaemun-Gu, Seoul 120-752,

Republic of Korea

^bDepartment of Emergency Medicine, Bundang CHA Hospital, CHA University College of Medicine, Bundang-Gu,

Seongnam-Si, Gyoenggi-Do 468-712, Republic of Korea

^cDepartment of Emergency Medicine, Soonchunhyang University Bucheon Hospital, Wonmi-Gu, Bucheon-Si, Gyoenggi-Do 420-767, Republic of Korea

Received 3 October 2010; revised 8 November 2010; accepted 16 November 2010

Abstract

Objectives: Metronome guidance is a simple and economical feedback system for guiding cardiopulmonary resuscitation (CPR). However, a recent study showed that metronome guidance reduced the depth of chest compression. The results of previous studies suggest that a higher chest compression rate is associated with a better CPR outcome as compared with a lower chest compression rate, irrespective of metronome use. Based on this finding, we hypothesized that a lower chest compression rate promotes a reduction in chest compression depth in the recent study rather than metronome use itself.

Methods: One minute of chest compression-only CPR was performed following the metronome sound played at 1 of 4 different rates: 80, 100, 120, and 140 ticks/min. Average compression depths (ACDs) and Duty cycles were compared using repeated measures analysis of variance, and the values in the absence and presence of metronome guidance were compared.

Results: Both the ACD and duty cycle increased when the metronome rate increased (P = .017, b.001). Average compression depths for the CPR procedures following the metronome rates of 80 and 100 ticks/min were significantly lower than those for the procedures without metronome guidance.

Conclusions: The ACD and duty cyle for chest compression increase as the metronome rate increases during metronome-guided CPR. A higher rate of chest compression is necessary for metronome-guided CPR to prevent suboptimal quality of chest compression.

(C) 2012

Introduction

The Quality of cardiopulmonary resuscitation (CPR) is a very important prognostic factor for cardiac arrest [1-3].

* Corresponding author. Tel.: +82 2 2228 2460; fax: +82 2 2227 9908.

E-mail address: [email protected] (T.N. Chung).

Many trials have been executed to improve the Quality of CPR using various Feedback devices [4-13]. Metronome guidance is a very cost-effective and feasible method relative to other feedback techniques. In addition, metronome guidance has been shown to improve the outcome of CPR [4-6]. Its ability to regulate the compression rate and ventilation has also been confirmed by multiple studies [4-6,13-15]. Furthermore, one

0735-6757/$ - see front matter (C) 2012 doi:10.1016/j.ajem.2010.11.026

study demonstrated that hyperventilation during CPR could be prevented by metronome guidance [13]. However, negative effects of this method have also been reported; one study reported that metronome guidance reduced the average depth of chest compression, which is an important quality factor for CPR [14]. Metronome-guided CPR may need to be discouraged if the negative effect on the depth of chest compression cannot be avoided because a sufficient depth is one of the most important factors affecting survival after CPR [16,17].

Oh et al [14] suggested that the reduction in the average chest compression depth (ACD) may be caused by the multitasking required by the simultaneous use of auditory perception and CPR technique. However, the exact cause of this reduction has not yet been elucidated. It is important to identify the cause to prevent the possible negative impact of metronome guidance on CPR.

There is a consistent finding among studies that evaluated the effect of metronome guidance on CPR; a higher chest compression rate was associated with a better CPR outcome than a lower chest compression rate, irrespective of metronome use [4-6,14]. However, there has been no study focusing on the effect of the metronome rate on metronome- guided CPR. Hence, we performed this study to evaluate whether the metronome rate affects the quality of closed chest compression during metronome-guided CPR.

Materials and methods

Study design

This study was approved by our institutional review board. This was a prospective, randomized, cross-over trial involving simulated 1 person CPRs.

Participants

Senior medical students from our institution who had finished their 2 mandatory CPR training courses, which were based on the American Heart Association basic life support course according to the 2005 American Heart Association guidelines for CPR and emergency cardiovas- cular care [18], within 1 year were enrolled in this study. Students who had a history of significant medical illness or were unable to perform high-impact exercise were excluded from this study. Informed consent was obtained from all participants.

Equipment

A Resusci Anne manikin with a PC Skill Reporting System (Laerdal, Stavanger, Norway) was used for measur- ing and recording CPR data. Metronome sounds were synthesized using the audio synthesizing software Reason

(Propellerhead, Stockholm, Sweden) with the signal proces- sing software package Waves gold bundle (Waves, Knox- ville, TN). Four different metronome rates were used: 80, 100, 120, and 140 ticks/min.

Study protocols

The participants performed 4 sets of Continuous chest compressions for 1 minute following the metronome sounds, which were played with rates of 80, 100, 120, and 140 ticks/ min in a random sequence. To avoid the effect of rescuer fatigue, sufficient resting time (more than 20 minutes) was guaranteed between the sets. In addition, 1 minute of chest compression was separately performed without metronome guidance or any additional instruction for the rate of chest compression as a baseline for comparison.

Measures

Average compression depth (mm), duty cycle (percent), a fraction of inaccurate hand positions (percent), and a fraction of incomplete releases (percent) were all measured using PC Skill Reporting System.

Data analysis

A repeated measure analysis of variance was used to compare the quality of chest compression for the CPR procedures following the increasing metronome rates. A paired t test was used to compare the quality of chest compression for each procedure with metronome guidance (80, 100, 120, and 140 ticks/min) with those in the absence of metronome guidance (baseline). A Friedman test and a Wilcoxon Signed Rank Test were used for nonparametric data. A Bonferroni correction was applied for multiple compar- isons. The data were considered significant when the P value was less than .05. A sample size of 27 and a power of 0.80 were calculated to detect a 15% difference in the ACDs for each procedure with metronome guidance (80, 100, 120, and 140 ticks/min).

Microsoft Office Excel 2007 (Microsoft Corporation, Redmond, WA) was used to record and analyze the data, and the Predictive Analytics Software Statistics 18.0 software package (SPSS Inc, Chicago, IL) was used for the statistical analysis. G?Power 3.1 (Heinlich-Heine Universitat, Dussel- dorf, Germany) was used to calculate the sample size [19].

Results

A total of 27 senior medical students participated in the study. The mean age of the participants was 24 +- 2 years, and there were 9 female participants (33%). The ACD signifi- cantly increased as the metronome rate increased (P = .017), following a linear trend (P b .001) (Fig. 1A). Duty cycle also

Fig. 1 Estimated marginal means of (A) average compression depths and (B) duty cycles according to the rate of metronome.

Table 1 Results of multiple comparisons with the procedures without metronome guidance

The rate of metronome

No metronome

80 ticks/min 100 ticks/min 120 ticks/min 140 ticks/min

significantly increased as the metronome rate increased (P b

.001), also following a linear trend (P b .001) (Fig. 1B). Fractions of inaccurate hand positions and incomplete releases were not significantly affected by increases in the metronome rate (P = .654, .504, respectively: results of nonparametric test). The ACDs for CPR procedures with metronome rates of 80 and 100 ticks/min were significantly lower than those for procedures without metronome guidance. The duty cycles for the procedures following metronome rates of 120 and 140 ticks/min were significantly higher than those for the procedures without metronome guidance. Fractions of inaccurate hand positions and incomplete releases did not identify any difference between these factors (Table 1).

Discussions

This is the first study to specifically evaluate the effect of the rate of metronome on the quality of CPR. Our results suggest that metronome guidance lowers the ACD when it occurs at a rate of 100 ticks/min, which is the current recommended chest compression rate. In fact, a rate higher than this is necessary to avoid lowering the ACD, which will ultimately lead to suboptimal chest compression.

This study was based on the previous study by Oh et al [14], which demonstrated that metronome-guided CPR reduced the ACD. Our results suggest that this negative effect might be caused by the difference in the rate of chest compressions between the metronome group and control group, rather than the use of metronome itself. This is supported by our multiple comparison analysis, which demonstrates that a significantly lower ACD was only observed in the CPR procedures following a rate of 100 ticks/min or below and not in procedures following higher rates.

Average compression depth (mm) a	43.4 +- 11.8	43.8 +- 13.3	45.3 +- 11.7	46.4 +- 11.4	47.4 +- 11.2
P value c	.005	.007	.128	.250	NA
Duty cycle (%) a	37.8 +- 7.0	41.5 +- 6.5	44.1 +- 50.4	47.1 +- 5.5	40.1 +- 5.8
P value c	.023	.117	b.001	b0.001	NA
Fraction of inaccurate hand positions (%) b	0.0 (1.0)	0.0 (0.0)	0.0 (0.0)	0.0 (0.0)	0.0 (0.0)
P value d	.753	.225	.696	.715	NA
Fraction of incomplete releases (%) b	0.0 (0.0)	0.0 (1.0)	0.0 (0.0)	0.0 (1.0)	0.0 (0.0)
P value d	.753	.086	.735	.515	NA
Average compression rate (numbers/min) a	79.1 +- 0.3	99.2 +- 0.5	119.5 +- 0.9	139.4 +- 1.0	109.7 +- 11.2
P value c	b.001	b.001	b.001	b.001	NA
NA indicates not applicable. a numerical values on table: mean +- standard deviation. b Numerical values on table: median (interquartile range). c Statistical significance under Bonferroni correction: P b .0125. d Results of nonparametric tests, statistical significance under Bonferroni correction: P b .0125.

A significant change in the ACD following an increase in the metronome rate is consistent with the results of Kern et al [4], which demonstrated a difference in end-tidal CO₂ (ETCO2) levels between CPRs guided by metronome rates of 80 and 120 ticks/min. The higher ETCO2 level in this study may be caused by deeper chest compressions. Furthermore, our results demonstrate not only a difference in ACDs between metronome rates but also a linear increase in ACD with increasing metronome rate. This suggests that restricting the compression rate to 100 ticks/min might reduce the ACD in the metronome guidance group, which is consistent with findings of Oh et al [14]. The relationship between the compression rate and ACD is supported by another result from our study: the duty cycles of chest compression increased with increasing metronome rate. The duty cycle approached 50% as the metronome rate increased, which is the duty cycle recommended by guidelines because of its simplicity [18]. This may provide the rescuer more comfort while performing chest compressions and may increase the effectiveness of their chest compressions. Further studies to clarify the relationship between the depth and duty cycle of chest compression are warranted.

Multiple comparisons of procedures following the 4 different metronome rates with those without metronome guidance demonstrated better performance in terms of duty cycles in the procedures following rates of 120 ticks/min or higher and worse performance in terms of ACD in the procedures following rates of 100 ticks/min or lower. This suggests that a higher rate than that recommended by the guidelines is required to improve metronome-guided CPR. Our data suggest that a rate of 120 ticks/min or higher should be used. Furthermore, it is much more difficult for an untrained person to achieve a certain compression force using a conventional compression rate [20]. This supports the necessity of using a higher compression rate with metronome-guided CPR, and guidance on the rate would be useful for the untrained person.

Fractions of inacurrate hand positions and incomplete releases were not affected by the different metronome rates or by metronome guidance itself, as demonstrated by the multiple comparison analysis. This result suggests that a higher rate of chest compression does not increase the error rate of chest compressions and may also support using a higher rate in metronome-guided CPR. However, rescuer fatigue was not considered in our study, and this may be aggravated by an increase in the rate of chest compression. However, Jantti et al [15] did not find that rescuer fatigue affected any quality indicators for participants who received and did not receive metronome guidance with CPR. Their average compression rates were quite different (137 +- 18 vs 98 +- 2), despite the significant difference in the subjective opinions of rescuer fatigue. Further evaluation of the use of high frequency chest compression in metronome-guided CPR, including the assessment for rescuer fatigue, is necessary.

The mean of average compression rates of the procedures without metronome guidance was higher than those with

metronome rate of 100 ticks/min but lower than those with metronome rate of 120 ticks/min in multiple comparisons. However, the mean of ACDs of the procedures without metronome guidance was not lower than those with metronome rate of 120 ticks/min and faster. This implies that the lower compression rate may not be an only mechanism explaining the poor performance of metronome guidance CPR shown in the previous study [14]. Further investigation will be needed.

In summary, the ACD is increased with an increase in the metronome rate without increasing the error rate of chest compression. Considering the positive effects associated with the ventilation rate and cost-effectiveness of metronome guidance [13,14], this technique can be considered as a useful adjunct for CPR if suboptimal chest Compression quality is prevented. This poor quality can be avoided if the metronome rate is increased.

Limitations

Our study has a few limitations. First, this was a manikin- based simulation study, which is quite different from the clinical setting, so there may be some difficulties in clinical application. However, this study focused on the performance of CPR and not on the response of patients. In addition, the simulation equipment used in this study has been well validated and routinely used to measure the performance of CPR. Hence, the results still have value for clinical application. Second, this study only compared CPRs with metonome guidance set at a few different rates and without metronome guidance. A study with more fractionated metronome rates and consideration for consistency in the actual compression rate and metronome rate is necessary for these results to be generalized.

Conclusions

The average depth and duty cycle of chest compression increase as the metronome rate increases during metronome- guided CPR. The average depth of chest compression is significantly lower in metronome-guided CPR with the rate set equal to or below the rate recommended by the guidelines (100 ticks/min). A higher rate of chest compression is necessary during metronome-guided CPR to prevent the suboptimal quality of chest compression.

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