British Journal of Anaesthesia 89 (3): 405-8 (2002)
Delays in defibrillation: influence of different monitoring
techniques
G. D. Perkins1*, C. Roberts2 and F. Gao1
Department of Intensive Care Medicine and Resuscitation Training Department, Birmingham Heartlands
Hospital, Bordesley Green East, Birmingham B9 5SS, UK
^Corresponding author
Background. Rapid defibrillation is the most important intervention required for a patient in
cardiac arrest due to ventricular fibrillation or ventricular tachycardia. Isolated case reports of
spurious asystole may have seen a change in practice, moving away from monitoring through
defibrillator paddles and gel pads in favour of attaching electrocardiograph (ECG) leads for the
initial monitoring of a collapsed patient. We surveyed current preferences for initial monitoring
and estimated the difference in time taken to deliver the first shock with the following three
monitoring techniques: defibrillator paddles and gel pads, ECG leads and hands-free adhesive
pads.
Methods. Sixty Advanced Life Support (ALS) course directors, selected at random, were
questioned to establish their current practice. Twenty ALS providers received 5 min revision in
the three techniques for the initial monitoring of a collapsed patient and were then randomly
tested to measure the time from confirmation of arrest to the first shock.
Results. Forty-two directors indicated their preferred methods for initial monitoring as 74%
leads, 21% paddles and 5% hands-free adhesive pads. Before testing, 10 providers preferred
paddles and 10 preferred leads. Monitoring through leads 54 (range 49-65) s was significantly
slower than paddles 28 (24-31) s, PO.0I and adhesive pads 23 (19-27) s, PO.0I. There was
no significant difference in the time taken between paddles and adhesive pads.
Conclusion. The current practice of monitoring through leads delays the time to deliver the
first shock. We recommend that initial monitoring through leads be discontinued in favour of
hands-free adhesivepads or defibrillator paddles/gel pads.
BrJ Anaesth 2002; 89: 405-8
Keywords: complications, cardiac arrest; equipment, defibrillators; monitoring,
electrocardiography
Accepted for publication: April 20, 2002
Since the first descriptions over 50 years ago, defibrillation
has become established as the standard treatment of a
patient in cardiac arrest due to ventricular fibrillation (VF)
or ventricular tachycardia (VT).1 The critical importance of
early defibrillation has been clearly shown in several large,
prospective clinical studies. Delays in defibrillation are
associated with poor outcome.2"5 Outside the monitored
environment of the operating theatre, coronary and intensive
care units, the underlying rhythm in the collapsed patient
needs to be determined rapidly. Three techniques are
currently available: defibrillator paddles and gel pads,
standard ECG leads, or hands-free adhesive gel pads.
In 1999 the medical devices agency issued a safety notice
warning that spurious asystole might be diagnosed in error
after attempted defibrillation using paddles and gel pads.6 A
further report was published shortly afterwards in the British
Medical Journal of a similar episode at a district general
hospital in England,7 when a patient was monitored using
gel pads with defibrillator paddles. After delivering a shock,
a period of apparent asystole was noted on the defibrillator
monitor (shown as a continuous or broken line); however,
simultaneous electrocardiographic (ECG) lead monitoring
with independent electrodes showed that the patient
remained in VF. Without additional monitoring with ECG
leads, a delay in the delivery of further shocks would have
resulted. Despite the limited number of reports of spurious
asystole in the literature,6"8 the wide publicity these reports
have received may have changed practice from the rapid
© The Board of Management and Trustees of the British Journal of Anaesthesia 2002
Perkins et al.
Table 1 ALS course directors' initial monitoring preferences
n (%)
ECG leads
Defibrillator paddles and gel pads
Hands-free adhesive pads
31 (74)
9(21)
2(5)
paddles/gel pad technique to monitoring initially through
standard ECG leads.
We set out to determine current preferences for the initial
monitoring of the collapsed patient and to measure the
difference in time taken to deliver the first shock with the
following three monitoring techniques: defibrillator paddles
and gel pads, ECG leads, and hands-free adhesive pads.
Methods
The study was divided into two parts. In the first part, 60
electronic questionnaires were sent to Advanced Life
Support (ALS) course directors selected randomly from
the Resuscitation Council UK register of course directors in
September 2001. Course directors are experienced ALS
trainers with medical, nursing or paramedical backgrounds
who have been granted permission to lead the Resuscitation
Council UK Advanced Life Support Provider Course. A
follow-up telephone call to non-responders was made 2
months later. The questionnaire asked the course directors
to specify their preference and teaching practice for the
initial monitoring of the collapsed patient.
In the second part of the study, 20 doctors or nurses were
recruited without prior warning to perform a defibrillation
test. All subjects had undertaken the Resuscitation Council
UK Advanced Life Support Provider Course and were
working at Birmingham Heartlands Hospital. The subject's
preference for initial monitoring was recorded before
testing. Five minutes of revision time was given in a
standardized manner, covering the three different techniques for initial monitoring that were to be tested. These
three techniques were: (i) defibrillator paddles and gel pads,
where gel pads (defib-pads; 3M, Germany) and defibrillator
paddles are placed on the patient's chest; (ii) ECG leads,
where three standard ECG (3M-red-dot; 3M, Germany)
electrodes are used for monitoring and gel pads/paddles are
used for defibrillation; and (iii) hands-free adhesive pads
(Multi-function Adult electrode pads; Hewlett Packard,
UK), which are adhesive electrode pads used for monitoring
and defibrillation. All tests were undertaken on a Laerdal
adult ALS manikin skill trainer using a Heartsim 200
rhythm simulator (Laerdal Medical, Norway). The
Codemaster XL (Hewlett Packard) defibrillator was used
for all tests, with default monitoring set to 'paddles' for
monitoring through paddles/gel pads, and 'leads' (lead II)
for ECG leads and hands-free adhesive pad tests. There was
-no significant difference in charge time between the
defibrillators used (2.4 (range 2.4-2.4) s for defibrillator 1
compared to 2.3 (2.3-2.4) s for defibrillator 2 during 10
successive shocks />>0.05). The training manikin is
designed to have the ECG leads attached directly onto the
chest wall and therefore it was not possible to obtain reliable
ECG signals by attaching the ECG electrode dots to the
ECG monitoring points. To reflect clinical practice, subjects
actually attached leads and electrodes to the manikin's
chest, but the ECG signal was fed directly to the defibrillator
after the third lead had been attached correctly.
The subjects were then presented with three simulated
defibrillation tests in a randomized order (block randomization). The manikin was stated to be in cardiac arrest and the
subject was required to establish initial monitoring, determine the underlying rhythm and deliver the first shock. The
time taken from the start of each test until the defibrillator
was charged to 200 J (as indicated by the defibrillator
audible warning bleep) was recorded.
Statistical analysis
Data were entered into Excel 97 (Microsoft, NY, USA) and
analysed using SPSS 10.0 for windows (SPSS Inc., Chicago,
IL, USA). Monitoring preferences from all subjects were
analysed using %2 and Fisher's exact tests. Defibrillation test
data were analysed for normality and found to be in a nonnormal distribution. Friedman's repeated measures analysis
of variance (ANOVA) on ranks with Dunnett's test was used
for multiple comparisons between the three monitoring
techniques. Data were expressed as medians (interquartile
range). A P value <0.05 was considered statistically
significant.
Results
In part 1 of the study, 42 (70%) course directors replied to
the questionnaire. The majority (74%) indicated that their
preferred method of initial monitoring of the collapsed
patient was ECG leads (Table 1). In part 2 of the study, 10
nurses and 10 doctors were recruited for the defibrillation
test. The median duration from attendance on the Advanced
Life Support Provider Course was 7.5 months (range 1^8
months). Ten subjects reported defibrillator paddles and gel
pads and 10 reported ECG leads as their preferred initial
monitoring technique. There was no statistical difference in
preferences between subjects trained >24 months previously
(i.e. before the first reports of spurious asystole) and those
trained more recently (P=0.63).
The time taken to deliver the first shock using ECG leads
was 54 (49-65) s compared with defibrillator paddles and
gel pads 28 (24-31) s; f<0.01 and hands-free adhesive pads
23 (19-27) s; P<0.01. There was no significant difference in
the time taken between paddles and hands-free adhesive
pads (Fig. 1).
406
Monitoring techniques and delays in defibrillation
— Median El Interquantile range "1
Maximum/minimum
120-i
P<0.01
P<0.01
I
10080-
60-
l_
40-
1
I
20-
I
i
I
NS
n
Paddles
Leads
Pads
Fig 1 Box plot of time taken to deliver first shock.
Discussion
The principal findings of this study are that contrary to
current guidelines,9 most ALS course directors recommend
that initial monitoring is performed using ECG leads. We
found that this delays the delivery of the first shock on
average by 26.4 s compared with defibrillator paddles and
gel pads, and by 31 s compared with hands-free adhesive
pads.
A potential limitation of our findings from the questionnaire survey to ALS course directors is the moderate
response rate. However, the clear preference (74%) for
monitoring initially through ECG leads amongst the
respondents suggests that this teaching practice is widespread. The second part of this, study consisted of a
simulated cardiac arrest using a resuscitation manikin and
has several inherent limitations. First, the prior revision and
controlled environment of the laboratory test is likely to
have shortened the time to first shock for all tests, as the
equipment was immediately available and defibrillator
operators were probably more relaxed than during a genuine
cardiac arrest. Secondly, the signal quality obtained through
the resuscitation manikin may be different from that seen in
clinical practice, although our experience is that it is similar
irrespective of which monitoring technique is used. The
poor quality signals seen when attaching ECG leads and
electrodes to the manikin may have artificially increased the
time taken to deliver the first shock with this technique.
However, this was identified in a pilot study and overcome
by feeding the electrical signal directly from the rhythm
simulator to the defibrillator during the actual study. Despite
these limitations, the findings of this study can probably
reasonably be extrapolated to the clinical environment.
After the early reports of spurious asystole, Bradbury and
colleagues conducted an in vitro study to investigate this
phenomenon.10 Using a low (50 Q) and high impedance
(1050 Q) defibrillator test model they measured the time
delay in the return of a test signal following defibrillation
through gel pads and hands-free adhesive pads. They found
significant delays (up to 61 s) in the return of the test signal
with the gel pad/paddle combination using the high
impedance test model after several shocks. This was caused
by retention of the electrical charge by the gel pads.
However, no such delays in the return of the test signal
occurred with the low impedance system or when handsfree adhesive pads were used with either system. As the low
impedance test model is closer to the reported mean
transthoracic impedance of patients in cardiac arrest,11
they concluded that the results supported their clinical
observations that spurious asystole is relatively rare in
practice. In addition spurious asystole occurs only after
several successive shocks so this should not influence the
choice of initial monitoring. If after two or three shocks the
rare phenomenon of spurious asystole is seen on the
monitor, then ECG lead monitoring should be rapidly
established.
Whilst our experience and that of others7 10 suggests that
spurious asystole occurs only rarely, no prospective studies
have formally investigated this phenomenon. A recent study
examining the recurrence of VF following defibrillation
with automated external defibrillators (and hands-free
adhesive pads) in the pre-hospital environment reported
delays in the recurrence of VF of >30 s in half of all the
patients studied.12 To our knowledge there have been no
reported cases of spurious asystole occurring with the
hands-free adhesive pads. The work by Bradbury and
colleagues10 suggests that it is unlikely to occur with this
device. However, only simultaneous ECG lead monitoring
can determine if some of these delays could be attributable
to spurious asystole, and further prospective studies are
required.
The choice of initial monitoring technique in cardiac
arrest is considered an important issue in resuscitation
training. We have recently reported that in a group of 25
ALS instructors, five considered that initial monitoring with
defibrillator paddles and gel pads without simultaneous
ECG lead monitoring constituted unacceptable performance,13 although current guidelines recommend the defibrillator paddles and gel pads technique for initial
monitoring.9 At present we are aware of only a handful of
high profile case reports reporting the phenomena of
spurious asystole.6"8 14 Monitoring though ECG leads may
delay defibrillation by on average 30 s. Early defibrillation
improves survival from cardiac arrest,2^4 n 16 and extrapolating the data presented in the modified Larsen model for
survival from cardiac arrest5 17 it can be anticipated that
delays in defibrillation of this order may reduce survival by
3.5-5%.
In the absence of convincing data that spurious asystole is
common, we recommend that in the unmonitored collapsed
patient, initial monitoring through leads should not be used,
and hands-free adhesive pads or defibrillator paddles and gel
pads should be; however, if asystole or apparent loss of
407
Perkins et al.
signal occurs after defibrillation with defibrillator paddles
and gel pads then monitoring with ECG leads should be
established as soon as possible. After the first three shocks
are given, the ECG leads can then be attached if appropriate
while basic life support is initiated. This recommendation is
consistent with the advice recently published in the
Resuscitation Council UK Instructor Bulletin.
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