Resuscitation 81 (2010) 343–347

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Resuscitation

j o u r n a l h o m e p a g e :

w w w . e l s e v i e r . c o m / l o c a t e / r e s u s c i t a t i o n

Simulation and education

Increase in pre-shock pause caused by drug administration before defibrillation:
An observational, full-scale simulation study

夽

Christian Bjerre Høyer

a

,

∗

, Erika F. Christensen

b

, Berit Eika

a

a

Centre for Medical Education, Faculty of Health Sciences, University of Aarhus, Aarhus N, Denmark

b

Department of Prehospital Medical Services, Central Region Denmark, Aarhus N, Denmark

a r t i c l e i n f o

Article history:
Received 22 August 2009
Received in revised form
12 December 2009
Accepted 30 December 2009

Keywords:
Information overload
Advanced life support (ALS)
Ambulance
Cardiac arrest
Cardiac massage
Cardiopulmonary resuscitation (CPR)
Chest compression
Circulation
Defibrillation
Education
Emergency treatment
Guidelines
Manikin
Resuscitation
Transport
Drugs
Pharmacokinetics
Crisis resource management

a b s t r a c t

Background: The importance of circulation during cardiopulmonary resuscitation has led to efforts to
decrease time without chest compressions (“no-flow time”). The no-flow time from the interruption of
chest compressions until defibrillation is referred to as the “pre-shock pause”. A shorter pre-shock pause
increases the chance of successful defibrillation. It is unclear whether drug administration affects the
length of the pre-shock pause. Our study compares pre-shock pause with and without drug administration
in a full-scale simulation.
Methods: This was an observational study in an ambulance including 72 junior physicians and a cardiac
arrest scenario. Data were extracted by reviewing video recordings of the resuscitation. Sequences includ-
ing defibrillation and/or drug administration were identified and assigned to one out of four categories:
Defibrillation only (DC-only) and drug administration just prior to defibrillation (Drug + DC) for which
the pre-shock pause was calculated, and drug administration alone (Drug-only) for which pre-drug time
was calculated.
Results: DC-only sequences were identified in 68/72 simulations, Drug + DC in 24/72, and Drug-only in
33/72. Median pre-shock pauses were 18 s (DC-only) and 32 (Drug + DC), and median pre-drug pause 6. The
variation between pauses was statistically significant (p

 0.001). DC-only and Drug + DC sequences was

found in 22/72 simulations. A statistically significant difference of 8 s was found between the median pre-
shock pauses: 17 s (DC-only) and 25 (Drug + DC) (p

 0.001). For un-paired observations, the pre-shock

pause increased with 78% and for paired observations 47%.
Conclusions: Drug administration prior to defibrillation was associated with significant increases in pre-
shock pauses in this full-scale simulation study.

© 2010 Elsevier Ireland Ltd. All rights reserved.

1. Background

The critical importance of sufficient circulation during car-

diopulmonary resuscitation has led to increased efforts to decrease
no-flow time.

1–5

No-flow time refers to the period during car-

diac arrest without sufficient circulation, and is equivalent to
the time without chest compressions. Several initiatives have
been taken to reduce no-flow time (also referred to as “hands-
off time”) in the treatment recommendations published by the
International Liaison Committee on Resuscitation (ILCOR). Based

夽 A Spanish translated version of the abstract of this article appears as Appendix

in the final online version at

doi:10.1016/j.resuscitation.2009.12.024

.

∗ Corresponding author at: INCUBA Science Park, Skejby, Brendstrupgaardsvej

102, DK-8200 Aarhus N, Denmark. Tel.: [phone].

E-mail addresses:

[e-mail]

,

[e-mail]

(C.B. Høyer).

on ILCOR recommendations, the European Resuscitation Council
(ERC) and the American Heart Association (AHA) now recommend
a compression–ventilation ratio of 30:2 (rather than previously
15:1), and only one defibrillation between each 2-min series of
basic life support (BLS) (rather than three).

6–12

Furthermore, the

AHA recently added a “hands-only CPR” recommendation to their
guidelines.

13

During advanced life support (ALS), BLS is interrupted every

2 min to assess the cardiac rhythm and to guide therapy. For
non-perfusing tachy-arrhythmias (e.g., ventricular fibrillation (VF)
and pulseless ventricular tachycardia), therapy includes defibrilla-
tion alone or drug administration and defibrillation together.

8,9,12

Defibrillation and drug administration are potentially life saving
actions, but they may also increase hands-off time if interrupting
chest compressions. Thus, it is necessary to weigh the disadvan-
tages of interrupting chest compressions against the advantages of
other actions.

0300-9572/$ – see front matter © 2010 Elsevier Ireland Ltd. All rights reserved.
doi:

10.1016/j.resuscitation.2009.12.024

344

C.B. Høyer et al. / Resuscitation 81 (2010) 343–347

Fig. 1. Comparison of advanced life support (ALS) guidelines. The figure shows the
interpretation of ALS guidelines from the American Heart Association (AHA), the
European Resuscitation Council (ERC), and the Norwegian Resuscitation Council
(NRC).

The no-flow time that starts from the interruption of chest

compressions until the delivery of DC-shock is referred to as the
pre-shock pause. A shorter pre-shock pause increases the chance
for successful defibrillation and, accordingly, the return of sponta-
neous circulation (ROSC).

14–17

Current recommendations state that

pre-shock pauses should not exceed 10 s.

18

The recommended timing for drug administration during ALS

differs between authorities, including the ERC, AHA, and the Nor-
wegian Resuscitation Council (NRC) (

Fig. 1

). The ERC and AHA

agree that drugs should be administered just before delivery of
DC-shock

9,12

; however, this apparent agreement encompasses two

different interpretations. As a safety precaution, the ERC dis-
courages touching the patient while charging the defibrillator

7,9

;

consequently, drug administration is to occur prior to charging the
defibrillator. In contrast, the AHA recommends continued chest
compressions – and therefore drug administration – during the
charge phase.

12

Yet another recommendation adds to the discor-

dance as the NRC recommend drug administration happens 60 s
after defibrillation, i.e., during the following cycle of BLS.

19

The rationale for delaying drug administration to 60 s after

defibrillation is dual. One part is pharmacokinetic and patho-
physiological aspects of resuscitation; the other is cognitive
considerations about complexity of guidelines.

The pharmacokinetic and pathophysiological arguments against

administering adrenaline just prior to defibrillation are, according
to the NRC, that myocardial perfusion ceases almost immediately
when chest compressions are interrupted,

20,21

and that it takes up

to 90 s to restore adequate perfusion of the heart after resuming
chest compressions.

20,21

Thus, adrenaline injected into a peripheral

vein only reaches its peak concentration after 90–150 s.

22

As such,

there may be no immediate benefit from adrenaline injected just
prior to defibrillation.

9

The cognitive considerations about guideline complexity can be

summarised to questioning if the focus on drug administration may
shift focus away from defibrillation and thereby increase the pre-
shock pause.

19

In theory, drug administration in itself should not significantly

influence the pre-shock pause since teams should use the BLS cycles
to prepare drugs for subsequent injection.

9

Further, intravenous

injection of 1 ml (as in the case for 1 mg adrenaline) should be very
quick, as should the mandatory saline flush

9

; however, it remains

unclear if drug administration affects the pre-shock pause in prac-

tice. Therefore, the aim of our study was to compare the pre-shock
pause with and without drug administration in a full-scale simula-
tion study.

2. Methods

The data used in this paper originated from our previous

observational study of junior physicians’ skills and behaviour dur-
ing simulated resuscitation.

23

The study included 72 participants

who had graduated within 5 years and were working in internal
medicine departments with acute admissions. Participation was
voluntary, informed consent was obtained, and data were kept
confidential.

The simulations took place in a working ambulance with gen-

uine equipment and personnel (a paramedic and an emergency
medical technician). A computer-controlled manikin with simu-
lated cardiac rhythm, respiration, peripheral blood saturation, and
blood pressure, was placed on the stretcher (ResusciAnne Simulator
& Laerdal PC SkillReporting System, Laerdal Medical, Norway). Sup-
plemental oxygen, intravenous accesses, electrocardiogram, and
self-adhesive defibrillation pads were established in advance.

The scenario involved a patient case with acute coronary

syndrome in need of percutaneous coronary intervention at a
specialised cardiac department. During transfer, the patient expe-
rienced a ventricular fibrillation (VF) cardiac arrest that was
refractory to treatment for 5 min. In the following 3 min, defibril-
lation would invoke ROSC. If not defibrillated within these 3 min,
ROSC would appear no later than 8 min after the onset of VF. In
all simulations, the used monitor/defibrillator, LIFEPAK-12 (Physio-
Control, USA) was of the same type and set to manual mode before
initiating the simulation (in contrast to advisory mode).

2.1. Data and statistics

Video recordings from a digital surveillance camera mounted

in the ambulance documented all simulations, and recordings
were continuously time-stamped by the camera with a built-in
on-screen digital clock. Calculation of intra- and inter-observer
variability was done by random selection of three simulations that
were reviewed (in their full length) twice by two independent per-
sons (a physician and a medical student) and by the first author of
this paper. The inter- and intra-observer coefficients were calcu-
lated using Stata/IC 10.1 (StataCorp, USA).

Events identified in the video recordings included time to onset

of VF, all ventilations, start/stop of all series of chest compressions
(including the number of chest compressions in each series), and
time for defibrillation and drug administration (

Fig. 2

).

Sequences that included defibrillation and/or drug administra-

tion were identified in the dataset and assigned to one out of
four categories: DC-only, Drug + DC, Drug-only, and Drug-during
(

Table 1

). If a pause in chest compressions included several defibril-

lations and/or several drug administrations or if in correct numbers
but in the wrong order, they were excluded.

Table 1
Defibrillations and/or drug administrations were assigned to one out of the four
categories listed in the table. The table shows the actions included in each of the
four categories.

Category

Action

Chest compressions

Drug administration

Defibrillation

DC-only

Interrupted

No

Yes

Drug + DC

Interrupted

Yes

Yes

Drug-only

Interrupted

Yes

No

Drug-during

Ongoing

Yes

No

C.B. Høyer et al. / Resuscitation 81 (2010) 343–347

345

Fig. 2. Example of registrations. The figure illustrates a segment of a simulation exercise. The diagonal numbers represent net time in the simulation, starting with the debut
of the ventricular fibrillation at the time 00:00:00 (hours:minutes:seconds).

For the two categories including defibrillation (DC-only and

Drug + DC), the pre-shock pause was calculated (

Fig. 3

). In order to

compare sequences including defibrillation and sequences includ-
ing drug administration, but not defibrillation, the term “pre-drug
pause” was introduced (

Fig. 3

): The pre-drug pause describes the

hands-off time from chest compressions are interrupted until drugs
are administered and thus represent an equivalent to the pre-shock
pause calculated in events including defibrillation. Time used for
drug administration during chest compressions (Drug-during) was
by definition zero.

In order to prevent results from being skewed by paired obser-

vations, the median value in each category (DC-only, Drug + DC,
and Drug-only) was calculated for each simulation: If a simulation
included more than one case in a single category, e.g. three cases
of defibrillation alone (DC-only), the median duration of the three
pre-shock pauses was calculated and used for further analysis.

Two comparisons were done: First, the duration of the median

pauses in the three categories (DC-only, Drug + DC, and Drug-only)

Fig. 3. Illustration of pauses and categories used in analysis. The upper part of the fig-
ure illustrates two different pre-shock pauses: upper left illustrates a sequence with
only defibrillation (DC-only) and upper right a sequence with drug administration
and defibrillation (Drug + DC). The lower left part of the figure shows a sequence of
a pre-shock pause, when only drugs are administered instead of a DC-shock, that is,
a pre-drug pause (Drug-only). The lower right of the figure illustrates drug injection
during chest compressions (Drug-during).

Fig. 4. Time in seconds since interruption of chest compressions to DC-shock
(DC-only (n = 68) and Drug–DC (n = 24)) or drug injection (Drug-only (n = 33)),
respectively. The three sequences depicted (DC-only, Drug + DC, and Drug-only) did
not necessarily happen in each simulation; consequently the numbers in each group
does not add up to the 72 simulations described. The differences were statistically
significant (one-way analysis of variances, p

 0.001). Values depicted are medians,

upper/lower quartiles, 5–95 percentiles (whiskers), and outliers (dots).

were compared using one-way analysis of variances. Second, intra-
individual comparison between the pre-shock pause in DC-only
and Drug + DC sequences was calculated for all simulations includ-
ing both DC-only and Drug + DC sequences using paired t-test. Both
comparisons were made using GraphPad Prism 5.02 (GraphPad
Software, USA). All time values are given in seconds as median
(lower; upper quartiles) [minimum–maximum].

3. Results

Almost all of the 72 simulations (68 (94%)) included DC-only

sequences, while only 24 (33%) included Drug + DC sequences.
Drug-only sequences were found in 33 (46%) of the simulations
(

Fig. 4

). Furthermore, 24 (33%) simulations included drug admin-

istration during ongoing chest compressions (Drug-during). The
three sequences (DC-only, Drug + DC, and Drug-only) did not nec-
essarily happen in each simulation; consequently, the numbers in
each group do not add up to the 72 simulations described

In the simulations including DC-only sequences (n = 68), the

median pre-shock pause for DC-only sequences was 18 s (14; 23)
[1–38]. In the 24 simulations including Drug + DC sequences the
median pre-shock pause for Drug + DC sequences was 32 s (21; 36)
[12–85]. Drug administration alone happened in 33 simulations
and had a median pre-drug pause of 6 s (3; 12) [1–41]. The difference
between the three groups was statistically significant (one-way
analysis of variances, p

 0.001) (

Fig. 4

). The relative increase in

346

C.B. Høyer et al. / Resuscitation 81 (2010) 343–347

Fig. 5. Pre-shock pause. The figure illustrates the pre-shock pause in the DC-
only and the Drug–DC-groups for the 22 simulations that included both type of
sequences. The difference in pre-shock pause was statistically significant (paired
t-test, p

 0.001). Values depicted are medians, upper/lower quartiles, 5–95 per-

centiles (whiskers), and outliers (dots).

pre-shock pause between DC-only and Drug + DC was 78% (14/18).

A total of 22 (31%) of the simulations included both DC-only

and Drug + DC sequences, which made it possible to compare intra-
individual differences between the pre-shock pause in DC-only
and Drug + DC sequences. In those 22 simulations, the median
pre-shock pause when only defibrillation was done (DC-only)
was found to be 17 s (15; 22) [6; 38] compared to 25 s (21;
36) [12–51] when drugs were administered prior to defibrillation
(Drug + DC) (

Fig. 5

). The difference in means was statistically sig-

nificant (p

 0.001, paired t-test).

Only two physicians performed the recommended flushing

with saline after drug administration. Raising the limb after drug
injection

9

happened only once.

The intra-observer variability coefficients were 0.9966, 0.9981,

and 0.9971, respectively, and the inter-observer variability coeffi-
cients were 0.9897, 0.9913, and 0.9906, respectively.

4. Discussion

In this observational, full-scale cardiac arrest simulation study,

we found an increase in the median pre-shock pause when
drugs were administered prior to defibrillation (25 s) compared
to defibrillation alone (17 s) in 22 simulations that included both
sequences. This 8-s difference in medians is equivalent to a 47%
relative increase (8/17) in the pre-shock pause. Further, compari-
son of all 72 simulations revealed a relative increase in pre-shock
pause between DC-only and Drug + DC at 78% (14/18).

This is an important finding given that a prospective, multi-

centre, observational study of cardiac arrest showed survival to be
71% if the pre-shock pause was within 10.2–20.0 s, but only 60% if
the it was within 21.1–30 s.

14

Pre-shock pauses shorter than 10 s might not be attainable in all

settings. We found pre-shock pauses of 17 and 25 s in the Drug-only
and Drug + DC groups, respectively, and our findings are supported
by those of other studies that found median pre-shock pauses of
15 s,

1

15.3 s,

14

11 s,

24

and 17 s.

25

The findings of pre-shock pauses longer than 10 s need attention.

One explanation is that the charging time of the defibrillator pro-
longs the interruption of chest compressions. This will be the case if
guidelines that discourage touching the patient during charging the
defibrillator are followed (ERC and NRC guidelines,

Fig. 1

). Another

explanation for longer pre-shock pauses may be inappropriately
designed equipment.

26

A third and perhaps more important explanation may be that

the less experienced physician needs more time than the more
experienced to assess the cardiac rhythm before deciding whether
defibrillation is appropriate.

In this study, we observed that performing two resuscitation

actions instead of one correlates with a significant increase in

pre-shock pause. Information overload, i.e., a situation with more
incoming stimuli than the physician has cognitive abilities to pro-
cess, may be one explanation.

27–30

Drug administration is not only a matter of emptying the

syringe, but also entails other actions, such as flushing with saline
(10–20 ml) and raising the limb in the air for 10–20 s.

9,12

Thus,

after deciding on appropriate drug administration, the physician
almost instantaneously has to estimate if this (injection, flush-
ing, raising the limb, etc.) will cause the patient to be left without
chest compressions for more than 10 s, and, in that case omit drug
administration.

9,12,18

To the experienced physician, such actions may be implicit,

but to the less experienced physician substantial efforts may be
necessary in order to recall these details. Further increasing the
number of information units to be processed within the very short
time frame from chest compressions are interrupted to defibrilla-
tion is supposed to be done, constitutes the core concept of “safe
defibrillation”. Safe defibrillation is advocated by the ERC, which
discourages touching the patient while charging the defibrillator
(

18

, pp. 82–83); however, the ERC also recommends administering

drugs while charging the defibrillator as a method of shortening
the pre-shock pause.

31

In our study we observed, that when drugs were administered

apart from defibrillation, but during a pause in chest compressions,
the median pre-drug pause was 6 s. Thus, performing one instead
of multiple procedures can be associated with shorter pauses in
chest compressions. This supports our concerns about informa-
tion overload under the current guidelines, a question also raised
by Meertens et al.

32

who suggested that drug administration just

before defibrillation may divert focus from defibrillation to drug
administration, thereby prolonging the pre-shock pause.

If the onset of the effects of adrenaline does not occur until

minutes after administration,

9,20–22

it should be carefully con-

sidered if this equals that the timing of administration could
be changed without negative consequences. It could be argued
that drug administration during BLS is merely relocating the time
without chest compressions. A counter-argument is the immense
impact that the length of the pre-shock pause has on the chance for
successful defibrillation.

In our study, we saw 24 simulations that included drug

administration during ongoing chest compressions (Drug-during).
One interpretation is that the physicians intuitively prioritised
chest compressions higher than drug administration and there-
fore chose to administer drugs during ongoing chest compressions
instead. Another, of course, would be that they did not know
guidelines.

A limitation in this study is that performance during simulation

is not equal to performance in real life. A manikin is not able to sim-
ulate all vital signs, skin pallor and temperature are just some of the
signs missing as well as it is clear that human life is not at stake.

33

The link between real life and the results presented in this paper is
that the simulations were held within the actual context. The setup
was a genuine ambulance, and the fellow players in the simulation
were real ambulance crews. The drugs, syringes, needles, and fluids
were real. Naturally, the manikin was not real. However, the chest
moved, the pulse was palpable — and vivid communications took
place between the physicians and the simulated patient through
the first minutes of the simulations.

Life-like surroundings and a patient case representing a frequent

challenge to the junior physician constitute a major strength to this
study. In the light of this, and the fact that simplified guidelines have
been shown to increase guideline adherence,

34–36

it seems reason-

able to carefully consider if it is possible to reduce the number of
actions to be performed during the pre-shock pause, thereby reduc-
ing information overload. In order to further elucidate this point, it
will also be necessary to perform studies that focus on only single

C.B. Høyer et al. / Resuscitation 81 (2010) 343–347

347

actions in order to decide whether the action by itself has latent
weaknesses.

5. Conclusions

Observations from our simulation study show that the pre-

shock pause is considerably longer in cases that include intravenous
drug administration prior to defibrillation (25 s) compared to cases
that include only defibrillation (17 s). Considering the recom-
mended maximum 10-s delay, both pauses were too long; however,
the delay related to drug administration is noteworthy as the pre-
shock pause represents time without sufficient circulation.

Our results suggest that altering the resuscitation sequence from

administering drugs before defibrillation to after defibrillation may
improve the outcome of resuscitation. As Kern et al. concluded
in 2002, “Any technique that minimizes lengthy pauses in chest
compressions [

. . .] should be given serious consideration”.

17

Conflict of interest statement

None to declare.

Acknowledgements

The authors wish to extend our greatest thanks to the enthu-

siastic ambulance crews for participating in the simulations and
to Peter G. Brindley MD, FRCPC, Division of Critical Care Medicine,
University of Alberta, Edmonton, Alberta Q1, Canada, for critical
review of the manuscript, as well as Anthony J. Handley MD, FRCP,
Colchester, England. Funding sources: This simulation study was
supported by a grant by the County of Aarhus, Denmark. Falck,
Denmark sponsored ambulances and personnel.

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