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ARTICLE IN PRESSG ModelESUS 5989 1–5
Resuscitation xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Resuscitation
j ourna l h o me pa g e : www.elsev ier .com/ locate / resusc i ta t ion
linical paper
ompressions during defibrillator charging shortens shock pauseuration and improves chest compression fraction during shockableut of hospital cardiac arrest�
heldon Cheskesa,b,c,∗, Matthew R. Commonc,d, P. Adam Byersc, Cathy Zhanc,aurie J. Morrisonb,c
Sunnybrook Centre for Prehospital Medicine, Toronto, ON, CanadaUniversity of Toronto, Division of Emergency Medicine, Toronto, ON, CanadaRescu Li Ka Shing Knowledge Institute, St. Michaels Hospital, Toronto, ON, CanadaInstitute of Medical Science, University of Toronto, Toronto, ON, Canada
r t i c l e i n f o
rticle history:eceived 16 January 2014eceived in revised form 8 March 2014ccepted 1 May 2014
eywords:ardiopulmonary resuscitationeart arrestesuscitationurvival
a b s t r a c t
Background: Previous studies have demonstrated significant relationships between shock pause durationand survival to hospital discharge from shockable out-of hospital (OHCA) cardiac arrest. Compressionsduring defibrillator charging (CDC) has been proposed as a technique to shorten shock pause duration.Objective: We sought to determine the impact of CDC on shock pause duration and CPR quality measuresin shockable OHCA.Methods: We performed a retrospective review of all treated adult OHCA occurring over a 1 year periodbeginning August 1, 2011 after training EMS agencies in CDC. We included OHCA patients with an initialshockable rhythm, available CPR process data and shock pause data for up to the first three shocks ofthe resuscitation. CDC by EMS personnel was confirmed by review of impedance channel measures. Weevaluated the relationship between CDC and shock pause duration as the primary outcome measure.Secondary outcome measures investigated the association between CDC and CPR quality measures.Results: Among 747 treated OHCA 149 (23.4%) presented in a shockable rhythm of which 129 (81.6%)met study inclusion criteria. Seventy (54.2%) received CDC. There was no significant difference betweenthe CDC and no CDC group with respect to Utstein variables. Median pre-shock pause (15.0 vs. 3.5 s; �11.5; 95% CI: 6.81, 16.19), post-shock pause (4.0 vs. 3.0 s; � 1.0; 95% CI: −2.57, 4.57), and peri-shockpause (21.0 vs. 9.0 s; � 12.0; 95% CI: 5.03, 18.97) were all lower for those who received CDC. Mean chestcompression fraction was significantly greater (0.77 vs. 0.70, � 0.07; 95% CI: 0.03, 0.11) with CDC. Nosignificant difference was noted in compression rate or depth with CDC. Clinical outcomes did not differbetween the two approaches (return of spontaneous circulation 62.7% vs. 62.9% p = 0.98, survival 25.4%
vs. 27.1% p = 0.82), although the study was not powered to detect clinical outcome differences.Conclusions: Compressions during defibrillator charging may shorten shock pause duration and improveschest compression fraction in shockable OHCA. Given the impact on shock pause duration, further studywith a larger sample size is required to determine the impact of this technique on clinical outcomes fromshockable OHCA.© 2014 Published by Elsevier Ireland Ltd.
Please cite this article in press as: Cheskes S, et al. Compreduration and improves chest compression fraction during shochttp://dx.doi.org/10.1016/j.resuscitation.2014.05.001
� A Spanish translated version of the abstract of this article appears as Appendixn the final online version at http://dx.doi.org/10.1016/j.resuscitation.2014.05.001.∗ Corresponding author at: Sunnybrook Centre for Pre-Hospital Medicine, 77rown’s Line, Suite 100 Toronto, ON, Canada M8W 3S2.
E-mail addresses: [email protected], [email protected]. Cheskes).
ttp://dx.doi.org/10.1016/j.resuscitation.2014.05.001300-9572/© 2014 Published by Elsevier Ireland Ltd.
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1. Introduction
Survival from out-of-hospital cardiac arrest (OHCA) continuesto challenge Emergency Medical Services (EMS) systems.1–3 Withthe advent of the 2010 American Heart Association-International
ssions during defibrillator charging shortens shock pausekable out of hospital cardiac arrest. Resuscitation (2014),
Liaison Committee on Resuscitation (AHA-ILCOR) guidelines forCardiopulmonary Resuscitation (CPR), interest has focused onimproving survival through improvements in CPR.4,5 Chest com-pression fraction (CCF), compression rate and depth, peri-shock
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ARTICLEESUS 5989 1–5
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ause duration and chest compression release velocity have alleen associated with improved survival to hospital discharge fromHCA.6–9 Shorter peri-shock pause duration and in particular pre-
hock pause duration have as well been associated with improvedeurological outcome from OHCA.10 Defibrillator mode (automaticr manual mode) is known to have a significant impact on pre-hock pause duration as a result of the mandatory time requiredor both defibrillator analysis and charging in automatic mode.10,11
variety of techniques have been shown to decrease pre-shockause duration when employed by providers in a simulated resus-itation environment.12 Chest compressions performed during theefibrillator charging phase (CDC) is one technique that has beenuggested in an attempt to mitigate the impact of defibrillatorharging time on pre-shock pause duration. Edelson et al.13 pre-iously have demonstrated significant improvements in pre-shockause duration by employing CDC in the inhospital environment.o previous studies have examined the impact of CDC performedy paramedics during OHCA. If CDC consistently shortens pre-shockause duration, it may have significant impact on both terminationf ventricular fibrillation and survival from OHCA. We thereforeought to explore the impact of CDC on shock pause duration andPR quality metrics during shockable OHCA.
. Methods
.1. Setting and design
The study took place in the Regions of Peel and Halton inhe province of Ontario, Canada. The regions cover an area of040 km2 and have a combined population of 1.6 million people.MS responds to a volume of 100,000 emergency calls per year.rehospital medical care is provided by advanced care paramedicsfull advanced life support skills) and primary care paramedicsbasic life support skills with the addition of a small number of
edications and manual defibrillation). Both agencies are part ofhe Resuscitation Outcomes Consortium (ROC), Toronto site, andarticipate in both ROC Epistry14,15 as well as all ROC cardiac ran-omized controlled trials. Since 2006, both agencies have collectedPR process data (chest compression rate, depth, CCF and shockause duration). Training in the technique of CDC occurred dur-
ng both EMS services’ continuing medical education immediatelyrior to the study start date of August 1, 2011. Training consistedf both didactic classroom instruction on the importance of min-mizing peri-shock pause duration and practical manikin-basedcenario training where paramedics learned to apply the CDC tech-ique during each shock delivered in a cardiac arrest resuscitation.oll E series defibrillators (Zoll Medical, Chelmsford, MA, USA) weremployed during the study period with no change in either hard-are or software configuration.
This study consisted of a retrospective review of prospectivelyollected data on the impact of CDC on shock pause duration, CPRuality metrics and clinical outcomes for a 1 year period beginningugust 1, 2011. The protocol was approved by the St. Michael’sospital Research Ethics Board (REB) as an amendment to eachgency’s pre-existing ROC REB approval.
. Study population
Patients eligible for this study included those 18 years of agend older who sustained non-traumatic OHCA with a first EMShythm of ventricular fibrillation or pulseless ventricular tachycar-
Please cite this article in press as: Cheskes S, et al. Comprduration and improves chest compression fraction during shochttp://dx.doi.org/10.1016/j.resuscitation.2014.05.001
ia (VF/VT) for which CPR process data for at least one shock wasbtained. The initial rhythm was determined to be VF/VT if the ini-ial rhythm was interpreted as VF/VT by the initial EMS providernd a shock was provided. Patients were excluded if they received
PRESSn xxx (2014) xxx–xxx
public access defibrillation before EMS arrival, or if their arrest waswitnessed by EMS.
4. Measurement
CPR process data from all eligible resuscitations were reviewedand assessed for duration of pre- and post-shock pauses, CCF, com-pression rate and compression depth up to and including onlythe third shock, to minimize confounding by other resuscitationinterventions (intubation, intravenous epinephrine or intravenousantiarrythmics). Pre-shock pause was defined as the time inter-val between chest compression cessation (as detected in theimpedance channel waveform) and shock delivery. Post-shockpause was defined as the time between shock delivery and chestcompression resumption (as detected in the impedance channelwaveform). Peri-shock pause was defined as the total of the pre-and post-shock pause time. CCF was defined as the proportionof time spent performing chest compressions during which thepatient was without spontaneous circulation.
All resuscitations were assessed for the presence or absenceof CDC. If chest compressions were clearly noted during the defi-brillator charging phase then the individual shock was noted tohave CDC. Resuscitations were either classified as CDC, if >50%of shocks delivered during a resuscitation demonstrated CDC, ornon-CDC if they did not. All resuscitations were assessed by twoinvestigators to ensure uniform classification with respect to thepresence or absence of CDC. The primary outcome measure wasthe relationship between CDC and shock pause duration. Secondaryoutcome measures investigated the association between CDC andCPR quality metrics (CCF, compression rate, compression depth).The relationship between CDC and clinical outcomes of return ofspontaneous circulation (ROSC) and survival to hospital dischargewere also examined.
5. Statistical analysis
Descriptive statistics were used to assess whether baselinecharacteristics remained consistent across study cohorts (CDC andnon-CDC). The relationship between CDC and all outcome meas-ures (median shock pause duration, CPR quality metrics, ROSC, andsurvival to hospital discharge) was calculated by univariate regres-sion analysis using a chi-squared test. To ensure our findings wererobust and not cofounded by the limitation of our analysis to thefirst three shocks of each resuscitation, we performed a secondaryper shock analysis on all shocks administered during the studyperiod to assess the association between shock pause duration andCDC. Study data management and storage was accomplished usingMicrosoft SQL Server 2008 (v.10.0.5848.0, Microsoft Corporation,Redmond, WA, USA), while statistical analysis was performed withSAS (v.9.3, SAS, Cary, NC, USA).
6. Results
Fig. 1 displays a CONSORT diagram of all cases included in thestudy. Of 747 treated, unwitnessed cardiac arrest resuscitations,20% had an initial arrest rhythm of VF/VT. Of those 149, CPR processdata was missing on 20 cases leaving 129 for analysis. Seventy (54%)of these cases were identified as CDC cases.
Table 1 compares the baseline characteristics of both studycohorts. No significant differences in Utstein variables or resusci-tation duration were noted between the two cohorts. Shocks per
essions during defibrillator charging shortens shock pausekable out of hospital cardiac arrest. Resuscitation (2014),
resuscitation and percent of shocks (first three) receiving CDC weresignificantly greater in the CDC then non CDC group.
Table 2 displays the association between CDC and median shockpause duration at the patient level (patients categorized as CDC or
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ARTICLE IN PRESSG ModelRESUS 5989 1–5
S. Cheskes et al. / Resuscitation xxx (2014) xxx–xxx 3
Fig. 1. Consort diagram of study cohort.
Table 1Study population baseline characteristics.
No CDC CDC p
n 59 70Age (mean) [year] 63.78 64.47 0.79Male [%] 77.97 74.29 0.63Public Location [%] 30.51 32.86 0.78Bystander witnessed [%] 71.19 70.00 0.89Bystander CPR [%] 50.85 52.86 0.82Response time (median) [min] 5.42 5.20 0.26Resuscitation duration (median) [min] 20.90 23.55 0.29Shocks per resuscitation (mean) 3.14 4.79 0.005First three shocks receiving CDC [%] 0.056 0.78 <0.001
CDC = compressions during charging; min = minutes.
Table 2Patient based univariate analysis of the impact of compressions during defibrillatorcharging on median shock pause duration.
No CDC CDC p value Difference 95% CI
Pre-shock pause (s) 15.0 3.5 <0.001 11.5 (6.81, 16.19)Post-shock pause (s) 4.0 3.0 0.11 1.0 (−2.57, 4.57)Peri-shock pause (s) 21.0 9.0 <0.001 12.0 (5.03, 18.97)
C
nmctSp
psabsts8
Table 3Shock based univariate analysis of the impact of compressions during defibrillatorcharging on median shock pause duration.
Non-CDC CDC p Difference 95% CI
n 314 159Pre-shock pause (s) 16 3 <0.001 13 (10.57, 15.43)Post-shock pause (s) 4 3 0.09 1(−0.68, 2.68)Peri-shock pause (s) 21 7 <0.001 14 (10.49, 17.51)
CDC = compressions during charging; s = seconds.
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DC = compressions during charging; s = seconds.
on CDC). Median values in the table represent the median of theedian individual case shock durations for all CDC and non-CDC
ases. Significant reductions in pre and peri-shock pause dura-ions were noted for CDC cases when compared with non-CDC.pecifically CDC cases demonstrated reductions in pre-, post- anderi-shock pause durations of 77%, 25% and 57% respectively.
Table 3 displays the association between CDC and median shockause duration incorporating all shocks administered during thetudy. In contrast to Table 2 this represents a shock based analysiss opposed to a patient based analysis of CDC. Similar to our patientased analysis, significant reductions were noted in pre- and peri-hock pause durations for shocks in which CDC occurred as opposedo shocks where CDC did not occur. Specifically CDC shocks demon-
Please cite this article in press as: Cheskes S, et al. Compreduration and improves chest compression fraction during shochttp://dx.doi.org/10.1016/j.resuscitation.2014.05.001
trated reductions in pre-, post- and peri-shock pause durations of1%, 25% and 67% when compared to non CDC shocks.
able 4nivariate analysis of impact of compressions during defibrillator charging on CPR qualityospital discharge.
No CDC C
Number of cases 59
CPR fraction 0.71
Compression depth (cm) 5.03
Compression rate (per min) 104.57 1ROSC 62.7%
Survival to hospital discharge 25.4%
DC = compressions during charging; CPR = cardiopulmonary resuscitation; ROSC = return
Fig. 2. Scatterplot showing shock pause duration vs. proportion of shocks per resus-citation where compressions during charging was used.
Table 4 displays the association between CDC and CPR qual-ity metrics (CCF, compression rate and compression depth) andthe selected clinical outcomes (ROSC, and survival to hospital dis-charge). A significant increase (p < 0.001, 95% CI (0.026, 0.11) in CCFof 8% was noted for CDC cases, whereas there was no apparent effecton chest compression depth or rate. No significant difference wasnoted in clinical outcomes between the two study cohorts.
Fig. 2 displays a scatterplot showing shock pause duration versusproportion of shocks per resuscitation where compressions duringcharging was used. Significant reductions are noted to occur in pre-and peri-shock pause duration as the proportion of shocks with CDCincreases. A subtle drop in post-shock pause duration is as wellnoted to occur.
7. Discussion
To our knowledge, this study represents the only out-of-hospitalstudy to date examining the relationship between CDC and shockpause duration, CPR quality metrics and clinical outcome measures.Study data analysis demonstrated significant improvement in bothshock pause durations (pre- and peri-) and CCF. These improve-ments persisted regardless of whether the analysis was performed
ssions during defibrillator charging shortens shock pausekable out of hospital cardiac arrest. Resuscitation (2014),
was no significant association between chest compression depth orrate; although in theory there is no physiological reason why CDC
metrics and clinical outcomes of return of spontaneous circulation and survival to
DC p value Difference 95% CI
700.77 0.003 0.06 (0.026, 0.11)5.36 0.066 0.33 (−0.20, 0.68)
06.73 0.37 2.16 (−2.43, 6.75)62.9% 0.99 0.2 (−0.17, 0.17)27.1% 0.83 1.7 (−0.14, 0.17)
of spontaneous circulation.
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hould impact these two variables. CDC, when performed properlyntuitively would decrease pre-shock and peri-shock interval yetn improvement in post-shock pause duration was also noted. It isur belief that paramedics who are focused on improving shockause duration and CPR quality by implementing interventions
ike CDC may be more focused on the importance of minimizingnterruptions during CPR, which may account for the benefit seenn post-shock pause duration in the cohort receiving CDC. Givenhe previously demonstrated associations between shock pauseuration, CCF and survival to hospital discharge8,10 it would seemlausible that CDC may impact critical clinical outcomes such asOSC and survival to hospital discharge. Unfortunately the sam-le size of our study was insufficient to adequately address thisuestion. Assuming an absolute improvement in survival of 5% inhe CDC cohort, a sample size of 2500 cases (alpha 5%, power 80%)ould be required to adequately power the study to detect differ-
nces in clinical outcomes. Due to the magnitude of the proposedample size, a large multi-center trial would be required. Based onrevious research demonstrating a reduction in survival of 7% forach 5 increase in pre-shock pause10, our findings of a 13 s decreasen median pre-shock pause by employing CDC has the potentialo improve survival by 18%. Few interventions in cardiac arrestesuscitation have the potential to improve survival by this degree.
Our findings are consistent with the findings of Edelson et al.13
ho were able to demonstrate that rescuer performance of chestompressions during the defibrillator “charging phase” signifi-antly lowered pre-shock pause intervals to less than 3 s (median.6 s; IQR: 1.9, 3.8). The improvement in pre-shock pause noted inhe Edelson study of 80% (13.3–2.6 s) was somewhat greater thanhe 64% improvement noted in our study and may be explainedy the lack of “run in” period after training for our paramedicroviders. Sell et al.16 discovered a significant relationship betweenre- and post-shock pause durations and the likelihood of ROSC inatients presenting in VF in a small study of OHCA resuscitations.eceiver–operator curves demonstrated an optimal pre-shockause duration of 2.3 s, which was only achievable by providerserforming CDC.
Defibrillator mode has long been noted to have a significantmpact on shock pause duration particularly automated exter-al defibrillators (AED). The mandatory time required for rhythmnalysis and defibrillator charging have been known to have a dele-erious impact on pre-shock pause duration.9–11,17 While CDC haseen shown to decrease pre-shock pause in AED mode, similaresults can be obtained by pre-charging the manual mode defibril-ator (pressing the defibrillator charge button prior to completionf the CPR cycle) thereby eliminating the defibrillator charge timefter rhythm assessment.12,13
Technological advances in defibrillator software which allowsnderlying rhythm analysis during CPR as well as defibrillatorharging and delivery of a shock immediately at the end of thePR interval could significantly decrease pre-shock pause intervalsbviating the need for CDC.18,19 Similarly, improved algorithmsllowing for earlier detection of shockable rhythms while work-ng in automated mode could also decrease pre-shock pause time.inally a new paradigm in defibrillator software voice promptsay exist particularly when providers work in AED mode. Voice
rompts have classically been programmed to state “Stop CPR”uring automatic defibrillator analysis and charging phase. Givenur study findings voice prompts stating “Continue CPR” duringefibrillator charging may be appropriate.
CDC and the quest for the shortest possible pre-shock pauseave raised concerns surrounding provider safety (inadvertent
Please cite this article in press as: Cheskes S, et al. Comprduration and improves chest compression fraction during shochttp://dx.doi.org/10.1016/j.resuscitation.2014.05.001
hock of provider performing compressions). A systematic reviewy Hoke et al.20 failed to substantiate these concerns. A very smallumber (15) of adverse events involving unintentional shockselivered to rescuers have been reported in this review since the
PRESSn xxx (2014) xxx–xxx
advent of widespread defibrillator use by medical personnel. Symp-toms consisting of tingling sensations, discomfort, and minor burnswere most common; in no case were any long term effects reported.Similarly Edelson et al.13 only noted one case of inadvertent shockadministration with no untoward effects. Our providers wore latexgloves during resuscitations and we are unaware of any incidentsof unintentional shock of providers during the study period.
Recent animal models and human feasibility models havedemonstrated the potential benefit and safety of completely elim-inating shock pauses via “hands on defibrillation”.21,22 Given thesurvival benefit to shortening pre-shock pause, further studyappears warranted to determine whether any survival benefitexists between a short pre-shock pause strategy using CDC and ano shock pause or “hands on defibrillation” strategy.
Our study has several limitations. After training in the techniqueof CDC only 54 percent of paramedics performed CDC during thestudy period. As the study period progressed, the proportion of CDCcases increased, indicating that providers were either becomingmore comfortable using the technique, or becoming more effectivein its application. We believe this trend may have been eliminatedby allowing a “run in” period for providers to get used to the tech-nique and maximize its use. Additionally, despite our training ofCDC to minimize pre-shock pause, some providers may have bal-anced the need to perform CDC to eliminate pre-shock pause witha concomitant concern of provider safety. Our decision to minimizedownstream resuscitation confounding (intubation, antiarrythmicuse, epinephrine use, in hospital care) by limiting our analysis toonly the first three shocks may have impacted the total numberof cases available by excluding shock pause intervals in prolongedresuscitations. The findings of our secondary shock based analy-sis employing all shocks provided during the study suggests thatour findings are in fact not confounded by limiting shock num-ber. Our study sample size was impacted by the relatively low rate(20%) of VF/VT in our study population. Our data is abstracted froman observational registry and as such we can only demonstrate anassociation between CDC performance and shock pause durationrather than a causal relationship. Lastly, the study took place inregions with high performing and heavily monitored EMS systemswith rapid response times and overall high CPR quality. The applica-bility of our findings to other EMS systems without similar systemresponse optimization and CPR quality characteristics is uncertain.
8. Conclusion
Compressions during defibrillator charging may shorten shockpause duration and improves chest compression fraction in shock-able OHCA. Further study with a larger sample size is required todetermine the impact of this technique on clinical outcomes fromshockable OHCA.
Conflict of interest statement
Dr. Cheskes has received speaking honorarium from Zoll Med-ical. Dr. Cheskes has received grant funding as Co PI, Toronto site,Resuscitation Outcomes Consortium. Dr. Morrison has receivedgrant funding as PI, Toronto site, Resuscitation Outcomes Consor-tium. No other grant disclosures.
Acknowledgements
essions during defibrillator charging shortens shock pausekable out of hospital cardiac arrest. Resuscitation (2014),
We would like to acknowledge the hard work and dedicationof all paramedics of both the Region of Peel Paramedic Serviceand Halton EMS. Research in the pre-hospital setting would notbe possible without the tireless efforts of their paramedics.
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