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Ventilation and Oxygenation Management 383

Oxygen Masks tilting their head slightly back and lifting the chin, or
Loose-fitting oxygen masks include simple (Hudson) face thrusting the jaw forward. The head-tilt/chin-lift mano-
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masks, aerosol masks used in combination with heated euvre is not used if cervical spine injury is suspected.
humidification and nebuliser treatments, tracheostomy The jaw-thrust manoeuvre may require two hands to
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masks and face tents. All are considered low-flow or maintain. If more prolonged support is required, an
variable-flow devices, with the delivered FiO 2 varying oro- or nasopharyngeal airway can be used that may also
with patient demand. Flow rates ≥5 L/min minimise CO 2 facilitate bag–mask ventilation.
rebreathing. The addition of ‘tusks’ to a Hudson mask
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may increase the oxygen reservoir, but does not guaran- ORO- AND NASOPHARYNGEAL AIRWAYS
tee a consistent FiO 2 and has probably been superseded The Guedel oropharyngeal airway is available in various
by high-flow systems. 12 sizes (a medium-sized adult requires a size 4). The airway
Partial rebreather and non-rebreather masks have an is inserted into the patient’s mouth past the teeth, with
attached reservoir bag that enables delivery of higher the end facing up into the hard palate, then rotated 180
levels of FiO 2 . Both mask types have a one-way valve degrees, taking care to bring the tongue forward and
precluding expired gas entering the reservoir bag. A non- not push it back. Oropharyngeal airways are poorly toler-
rebreather mask has two one-way valves on the mask ated in conscious patients and may cause gagging and
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preventing air entrainment. The maximum FiO 2 deliv- vomiting.
ery with non-rebreather masks is 0.85 with low flow A nasopharyngeal airway (see Figure 15.1) is inserted
demand, with a steep decline in FiO 2 concentration at through the nares into the oropharynx; it can be difficult
the alveoli level as the patient’s minute volume increases. to insert and require generous lubrication to minimise
Non-rebreather masks may perform worse than a Hudson trauma. This type of airway should not be used for
mask without a reservoir bag. 5 patients with a suspected head injury. As well as opening
Venturi Systems the airway, suction catheters can be passed to facilitate
secretion clearance. Once inserted these airways are better
Venturi systems use the Bernoulli Effect to entrain gas via tolerated than an oropharyngeal airway.
a side port; gas flow through a narrowing increases speed
and gains kinetic energy, resulting in an area of low pres- LARYNGEAL MASK AIRWAY
sure that entrains room air through the side port. An FiO 2
concentration can be selected by widening or narrowing AND ITS INTUBATION
the aperture in the Venturi device to a maximum FiO 2 of The classic laryngeal mask airway (cLMA) (see Figure
0.6. The FiO 2 concentration using a Venturi system is less 15.2) is positioned blindly into the pharynx to form a
affected by changes in respiratory pattern and demand low-pressure seal against the laryngeal inlet. It is easier
compared to other low-flow oxygen devices. 5 and quicker to insert than an endotracheal tube, and is
particularly useful for operators with limited airway skills;
Bag–Mask Ventilation the cLMA does not carry the same potentially fatal com-
Bag–mask ventilation (BMV) with a self-inflating bag plications such as oesophageal intubation although the
(and reservoir), non-return valve and mask delivers risk of aspiration remains. 17
assisted ventilation at an FiO 2 of 1. Addition of a positive Mechanical ventilation can be delivered with low-airway
end-expiratory pressure (PEEP) valve will improve oxy- pressures (less than 20 cmH 2 O) via a cLMA. This device
genation. Manual ventilation requires a good seal between is widely used in elective general anaesthesia, and can
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the patient’s face and the mask; this may be difficult to be used in critical care as an alternative to bag–mask
achieve as a single operator. One person may be required ventilation or endotracheal intubation when initial
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to hold the mask and lift the patient’s chin, while another attempts at intubation have failed. The ‘intubating’
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squeezes the bag. Effective bag–mask ventilation is con- LMA is most commonly used when a difficult
firmed when the chest visibly rises as the bag is squeezed intubation is anticipated or encountered. This device
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as well as improved oxygen saturations. BMV may cause has a handle and is more rigid, wider and curved than
gastric insufflation, increasing the risk of vomiting and the cLMA, enabling passage of a purpose-made endo-
subsequent aspiration. tracheal tube. 17

COMBITUBE
Practice tip
The combitube is more widely used in North America for
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Transparent face masks are recommended for bag–mask venti- emergency situations than in Australia and the UK. It is
lation as they allow immediate recognition if a patient vomits. a dual-lumen, dual-cuff oesophageal-tracheal airway that
enables ventilation if inserted into either the oesophagus
or trachea. Inexperienced operators may find a combi-
AIRWAY SUPPORT tube more difficult to insert correctly than a cLMA.
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Complications may occur in up to 40% of patients and
The most common cause of partial airway obstruction in include aspiration pneumonitis, pneumothorax, airway
an unconscious patient is loss of oropharyngeal muscle injuries and bleeding, oesophageal laceration and perfo-
tone, particularly of the tongue. This may be alleviated by ration and mediastinitis. 20