Ambulance

Clinical Focus on Emergency Artificial Ventilation
This device and others like it have been
widely used in anaesthetic rooms and in
both hospital and prehospital emergency
medicine since that time 6 . In conjunction
with a pharyngeal mask, the bag-valve-mask
is probably the mostly widely-used device to
provide positive pressure ventilation in the
world today. (Figure 2)
Figure 2: The BV device with the Ruben
non-return valve (1) pharyngeal mask (2)
filter and non-return valve (3) self-reforming
bag. (Photograph by courtesy of AMBU,
Copenhagen, Denmark)
Perceptions of safety and
effectiveness of bag valve mask
ventilation
There are a number of reasons for the
widespread adoption of the BVM by
paramedical and other emergency services
which include the following:
1 It had an apparent simplicity of action
with either one hand holding the mask
while the other squeezed the bag (single
operator) or two hands holding the mask
( the so-called ‘ double C ‘ position) and
another person squeezing the bag 2 .
2 There was a belief that in squeezing the
bag manually there was a feeling of being in
‘direct contact ‘ with the patient’s lungs and
therefore over-ventilation would be avoided
3 There was a conviction that the device
was essentially safe to use and could provide
effective ventilation. This was probably
based upon the fact that that bag ventilation
is used following the induction of general
anaesthesia in the anaesthetic room on
patients who are asleep, have muscle
relaxation and usually an empty stomach.
Many of these patients would also have
normal values of airway resistance and lung
compliance. It was in this environment that
many paramedics first received their airway
and ventilation training.
4 Compared with mechanical ventilators
providing BVM involved a low financial
outlay. The development of disposable BVM
at the end of the 20th century provided
a solution to sterilisation with increasing
concerns about cross-infection.
Problems associated with the use of
the bag-valve-mask device
Despite continuing widespread use of the
BVM in emergency ventilation (particularly
Spring 2016 | Ambulancetoday
in the United States, where the adoption of
alternative portable automatic ventilation
has been relatively slow) there has been
increasing concern over the past decade
about potential serious problems that
may be associated with this type of
positive pressure ventilation. These may
be summarised as hypo - and hyper -
ventilation.
Hypoventilation
The BVM usually operates using air as
the main gas with supplemental free-flow
oxygen provided to increase the oxygen
concentration. However this can cause
considerable wastage of bottled oxygen due
to leaks around the mask (particularly if held
with only one hand). In addition, if the mask
seal is not effective too low a tidal volume
will be delivered to the patient leading to
hypoventilation and hypoxia.
Hyperventilation
Inappropriate use of the BVM may cause
(1) high ventilation frequency and tidal and
minute volumes and (2) excessive inflation
pressures. These can cause gastic insufflation,
barotrauma, where weak sections of the
lung parenchyma are disrupted, leading
to pneumothorax and the more recently
recognised problem of volutrauma,
where damage is caused to the alveoli
by over-distension. In addition, excessive
intrathoracic inflation pressures have
important haemodynamic consequences.
High ventilation rates
Ventilating the patient too quickly, even if the
tidal volume is correct leads to an excessive
minute volume and hypocapnia. Even with
trained and experienced operators the
stressful nature of the emergency situations
where BVM are used can lead to high
ventilation rates. Cooper et al 7 noted that
keeping artificial ventilation rates low is
difficult because the high adrenaline state of
the rescuer alters time perception, and that
the rapidly refilling bag provokes a reflex
in which rescuers are inclined to deliver
breaths as soon as the bag inflates.
Aufterheide et al 8 reported a clinical
study observing ventilation rates in cardiac
arrest patients. They found that emergency
medical services (EMS) rescuers using a bag
valve device who were trained to follow
the American Heart Association (AHA)
guidelines were delivering on average 37±4
breaths per minute, not the 10–12 breaths
per minute prescribed by the guidelines.
Even after the rescuers were re-trained to
deliver 12 breaths per minute, they were
observed delivering an average of 22±3
breaths per minute.
Losert et al 9 demonstrated excessive
ventilation rates with BV devices even
among trained intensivists, most of whom
were basic or advanced life support
instructors. Their study demonstrated that
the respiration target rate was achieved
only 18% of the time in patients receiving
cardiopulmonary resuscitation, even when
performed in a hospital setting. On average
the guideline for correct ventilation rate was
exceeded by 33%.
O’Niell and Deakin 10 studied BVM in
comparison with a manually triggered
ventilator and an automatic transport
ventilation. They found that hyperventilation
was common with the BVM but mainly due
to high respiratory rates (ranging from 9
– 41 breaths per minute) rather than from
excessive tidal volumes.
Excessive inspiration pressure
Several studies have demonstrated excessive
inspiration pressures using bag valve devices
which can cause barotrauma and gastric
insufflation
There has been a long-standing fear that
in patients with an unprotected airway
excessive airway pressure caused by
squeezing the bag too hard would open
the oesophageal sphincter and cause
inflation of the stomach, leading to potential
regurgitation and aspiration into the lungs.
This was a particular concern in patients
being resuscitated following cardiac arrest
Updike and colleagues 11 studied the use of
the BVM in comparison with a manuallytriggered
ventilators and an automatic
transport ventilator. All three devices
delivered similar tidal volumes when used
by emergency medical technicians the BV
device was associated with a high PAP,
mask leak and gastric insufflation. The latter
problem has long been a major concern
when ventilating through an unprotected
airway such as a pharyngeal mask 12 – 14 . Salas
et al 12 , reporting a study measuring the
differences between a bag valve device and
a transport ventilator used with a mask
found that almost 10 times the amount
of air was insufflated into the simulated
stomach per breath when the subjects used
a bag valve device.
Haemodynamic effects of increased
intra thoracic pressure when using a
bag valve device
There are a number of studies which
have investigated the effects of excessive
intrathoracic pressure on the circulation
when venous return to the heart is
impaired. These can have serious
consequences in hypovolaemic patients
following physical trauma. Cheifz et al 15
noted that hyperventilation results in
high intrathoracic pressure during the
decompression phase of cardiopulmonary
resuscitation (CPR), which decreases cardiac
pre-load and cardiac output and impedes
right ventricular function. Increased tidal
volume is also known to adversely affect
cardiac output. These authors believe that
“the elevated mean intrathoracic pressures
caused by excessive ventilation inhibited
venous blood flow back to the right heart,
as there was insufficient time to allow for
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