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S Afr Fam Pract
ISSN 2078-6190 EISSN 2078-6204

NW REFRESHER COURSE

Cardiopulmonary resuscitation (CPR) has over the past 60 years
become an ubiquitous skill amongst medical professionals and
laypeople alike. Over the past several decades, a number of
different research findings have led to fundamental changes in
the methods used in attempts to reverse cardiac arrest. In order
to understand our current practice, it is important to have a firm
grip on the history of modern resuscitation.

CPR is comprised of 3 individual components; rescue breathing,
compressions, and defibrillation. Each of these developed
separately, in some cases over hundreds or even thousands of
years.1 Following a spate of drownings across Europe in the 18th
century, the Paris Academy of Sciences (Académie des Sciences)
in 1740 issued a recommendation for the use of mouth-to-mouth
resuscitation in drowned victims.2 In 1744, the first successful
use of this method in a human was documented by Tossach.1
Thereafter a number of different ventilation approaches were
attempted, and it took more than 200 years before mouth-to-
mouth and mouth-to-airway were shown to be the most efficient
methods of artificial respiration.3

At around the same time, several investigations into the effect of
electric shock applied to the myocardium brought forth the next
leap forward in resuscitation science – defibrillation. In 1956, Zoll
published his seminal paper detailing four patients in ventricular
fibrillation who had been defibrillated, one of whom survived to
discharge.4 Despite this discovery it wasn’t until the 60s that the
various components of CPR began to be utilised together.

During defibrillation experiments on dogs, Kouwenhoven had
noted that the pressure of the heavy paddles increased blood
pressure, and that rhythmic pressure to the sternum maintained
cerebral blood flow.5 In 1960, he published his now famous
article describing ‘closed-chest cardiac massage’ – so named
because prior to this direct cardiac massage through an open
chest had been the mainstay of cardiac arrest management.6
A flurry of investigations and publications followed, which
suggested a compression rate of 60 to 80 per minute, and a
compression depth of 4 to 5 centimetres paired together with
artificial respiration, as well as defibrillation and administration
of vasopressors as the optimal approach to resuscitation.7

A few years later, in 1966, the first CPR guidelines were published
and quickly spread worldwide.8 Of note is that even at this
early stage of modern CPR the danger of delay in initiation of

resuscitation was clearly recognised as a poor prognosticating

factor.9

In 1957, Safar published the ‘ABC of Resuscitation’ which

subsequently informed the stepwise approach of ‘Airway-

Breathing-Circulation’ by which CPR would be performed into the

21st century.10 Up until 2005, this approach emphasised opening

of the airway followed by assessment of breathing, rescue

breaths as required, and then a circulatory assessment usually

in the form of a pulse check, followed by chest compressions as

required. In 1982, the Netherlands, noting experimental data

which showed no significant drop in PO2 and O2 saturation in

the first 5 minutes after arrest, changed their CPR algorithm from

an ABC approach to a compressions-airway-breathing (CAB)

approach. They found that starting chest compressions first

resulted in quicker restoration of coronary perfusion pressure

and more chance of successful defibrillation.11 At the time, the

Netherlands was the only country following this approach,

briefly adopting the ABC approach to fall in line with European

Resuscitation Council (ERC) guidelines before reverting to CAB

with the 2005 ERC guidelines.

The Dutch decision has since been supported by evidence which

shows that in animal models and human studies defibrillation

performed from 3 to 5 minutes after arrest is more likely to

result in return of spontaneous circulation (ROSC) if at least 90

seconds of CPR is completed immediately prior to shock. This

finding is best described by a 3-phase time based physiological

model of CPR divided into the electrical phase, the circulatory

phase, and the metabolic phase. The electrical phase extends

from the time of arrest to approximately 4 minutes thereafter

and refers to a period during which the heart is exceptionally

responsive to defibrillation. This explains the success of early

external defibrillation as well as various devices including

implantable cardioverter defibrillators (ICD). The circulatory

phase, which runs from 4 to 10 minutes, is the time during which

chest compressions are crucial to provide much needed oxygen

amongst other substrates to the myocardium. In addition,

the forward flow created by quality CPR allows for washout of

various metabolic toxins which accumulate during ischaemia.

The period after roughly 10 minutes following arrest is called the

metabolic phase, during which it becomes increasingly difficult

to adequately overcome the systemic metabolic derangement,

South African Family Practice 2019; 61(2):S44-S46

Open Access article distributed under the terms of the
Creative Commons License [CC BY-NC-ND 4.0]
http://creativecommons.org/licenses/by-nc-nd/4.0

CPR: ABC or CAB
Witt J

Department of Anaesthesia, Chris Hani Baragwanath Academic Hospital,University of the Witwatersrand, South Africa
Corresponding author, email: wittjon@gmail.com

CPR: ABC or CAB 45

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resulting in a massive inflammatory response, translocation of

gut flora and irreversible tissue damage.12

Given this background, the importance of compressions as

the single greatest intervention in cardiac arrest, along with

defibrillation, has become clearer and more evidence-based in

the past 20 years. The University of Arizona Sarver Heart Center

Resuscitation Group pioneered the concept of cardiocerebral

resuscitation (CCR). This method focuses on continuous

compressions stopping only for rhythm checks and defibrillation

as required so as to minimize the time spent off the chest.13

This is because continuous uninterrupted chest compressions

have been shown to result in physiologically appropriate

perfusion pressures which can and do lead to ROSC.14 In fact,

multiple studies have repeatedly shown that CPR with a focus

on chest compressions, whilst keeping interruptions to an

absolute minimum, increase the chances of ROSC and improve

neurological outcomes as well as patient survival.15,16 During

CPR, it takes about 45 seconds of continuous chest compressions

to reach an optimal perfusion pressure. Therefore, any time taken

before the initiation of chest compressions, including the first 45

seconds of those compressions, are periods of non-perfusion.17

This information has greatly influenced the 2 major changes to
CPR which took place in 2005 and 2010 respectively. The first
of these was a move from a compression to ventilation ratio of
15:2 to that of 30:2 for single rescuers of victims of all age groups
except neonates.18 This change was justified by low CPR survival
rates and the aforementioned evidence which highlighted
improved coronary perfusion pressure and cardiac output

with an increasing number of consecutive high quality chest
compressions.19 The second and arguably more controversial
change was the move away from the ABC approach which
had remained in place globally until 2010. The International
Liaison Committee on Resuscitation (ILCOR) changed this
recommendation to that of a CAB approach, emphasising that
compressions should be of adequate rate and depth, allow
for full chest recoil and minimize interruptions. This was done
with the simultaneous removal of a step providing for initial
rescue breaths prior to any chest compression.20 The overriding
justification for the implementation of CAB is the significantly
shortened delay in starting compressions21 and a reduced time
to complete a cycle of compressions and ventilations.22

In 2015, ILCOR again released updated guidelines in which they
continued to suggest CAB over ABC but noted the need for
more evidence to improve the strength of the recommendation.
Of note is that the approach to paediatric patients is left up to
individual resuscitation councils, meaning that ABC may be
recommended in this age since a greater number of arrests
are hypoxia related.23 It has however been shown that even in
paediatric resuscitation rescuers identify the condition quicker,
make fewer mistakes using the CAB sequence, and that this
approach does not delay ventilatory support as compared to
ABC.24 Further additions to the 2015 guidelines with regards to
compressions are the inclusion of a range for compression rate
from 100 to 120 per minute, a maximum compression depth of
6 cm in adults, and the introduction of a compression fraction
whereby chest compressions during CPR should comprise
at least 60% of the total time in a resuscitation.25 Following a
CAB approach makes it somewhat easier to achieve a higher
compression fraction.

The CAB mnemonic has had the effect of de-emphasising
the role of airway management during CPR. Under the ABC
approach, and until 2005, opening of the airway and assessing
the patient for breathing, independent from any signs of
circulation, was a standard of care. The 2005, 2010, 2015, and
the latest 2017 guidelines all downplay the role of airway
interventions in lieu of adequate chest compressions.26 The
belief that advanced airway techniques such as endotracheal
intubation (ETI) or insertion of a supraglottic airway (SGA) is
superior to bag-mask ventilation (BMV) is inconsistent with the
available evidence, which currently indicates that advanced
airway management during CPR is associated with lower survival
rates.27 In a large cohort study of more than 86 000 patients,
intubation within the first 15 minutes of CPR was associated with
a significant reduction in survival to hospital discharge.28 This is
most likely because intubation interrupts chest compressions by
as much as 110 seconds in the average patient,29 even though
current guidelines recommend that ETI should never interrupt
compressions for more than 5 seconds.30 More recently, the use
of video laryngoscopy (VL) in resuscitation has been compared
to that of traditional direct laryngoscopy (DL). The literature is
conflictory with some evidence suggesting greater first attempt
success rates, most especially in less experienced clinicians,31
while another study showed no difference between VL and DL
in ETI success, although VL did cause fewer interruptions of chest
compressions.32

Figure 1: Perfusion pressure gradually increases with the initiation
of chest compressions. Interruptions in chest compressions cause a
sudden loss of this pressure17

Figure 2: Prolonged interruptions in chest compressions lead to even
greater periods of inadequate perfusion17

S Afr Fam Pract 2019;61(2)46

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At best when compared to BMV, the use of ETI shows no benefit
over the more basic technique in a good example of clinical
equipoise.33 A related issue is that poor ventilation technique in
cardiac arrest, which commonly includes hyperventilation, has
poor survival outcomes.34 This is due to various physiological
derangements, most notably increased intrathoracic pressure
leading to decreased cardiac output, coronary and cerebral
perfusion.35 The best approach to airway management
remains unclear and there is a paucity of data with regards to
CPR in the operating theatre when this process is performed
by anaesthesiologists. Much of the data available for airway
management during cardiac arrest is derived from out of hospital
studies and then extrapolated for in-hospital practice.36 Further
investigation is thus required, but it is clear that instrumentation
of the airway should not detract from time spent on the chest.

Since the invention and popularisation of CPR in the 1960s
much has changed, and steady strides have been made in
understanding the best approach to the patient in cardiac arrest.
The CAB approach is part of this evolution, which now places
emphasis on chest compressions, crucial in the initial phases of
an arrest. Whilst ABC in this context serves a similar purpose, it
likely delays the initiation of CPR thereby worsening outcomes,
making CAB a more pragmatic and evidence-based approach to
resuscitation.

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