________________________

SECTION 6SECTION 6

(SOME PRACTICAL ISSUES)

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CHAPTER 37 - AIRWAY ASSESSMENT AND MANAGEMENT

Airway assessment

Careful assessment of the airway is an essential component of every preoperative visit. Difficulty in airway

management is the single most important cause of anaesthesia-related morbidity and mortality. It has been

estimated that as many as 30% of deaths totally attributable to anaesthesia are associated with inadequate airway

management.

The site and nature of the proposed surgery, the type of anaesthetic selected, and patient factors will determine a

plan for airway management by the anaesthetist.

It may be obvious that a patient's airway will be difficult (e.g. masses, abscesses, anatomical abnormalities, etc.),

but most catastrophes happen when unexpected difficulty occurs. Assessment of the airway involves taking a

history, examination, and the use of a few simple bedside tests.

History

Ask about previous anaesthetics and scrutinize previous anaesthetic records. Check for previous airway

problems. If the patient was intubated there should be a comment about the best view obtained of the

glottis as graded by Cormack and Lehane1 (see p. 867, Fig. 37.1).

When airway or intubation problems have been recorded, were they related to an acute event (e.g. trauma,

airway disease process, pregnancy) or is the underlying problem still present?

Is there a history of dental damage or severe sore throat with previous anaesthetics?

Ascertain whether the patient has had previous head and neck surgery, radiotherapy to the head and neck,

or has medical conditions that may predispose to difficult tracheal intubation-diabetes mellitus,

acromegaly, rheumatoid arthritis, cervical arthropathy, morbid obesity, or obstructive sleep apnoea.

Patients with Down's syndrome or degenerative cervical spine disease are at increased risk of atlantoaxial

instability.

An occasional patient may have written notification of previous airway problems.

Examination

Look for neck masses, scars of previous head and neck surgery, burns, or the skin changes associated with

radiotherapy.

Adverse anatomical features include a small mouth, receding chin, high arched palate, large tongue, bull

neck, morbid obesity, and large breasts.

Look for protruding/awkwardly placed or loose teeth. Document the position of any caps or crowns

and inform the patient of the risk of damage to these.

Note the position of the larynx and trachea and the accessibility of the cricothyroid membrane.

Look out for patients with beards (which may hide adverse anatomical features) or occipital hair buns

(which may prevent extension at the craniocervical junction).

If the nasal route is chosen for intubation remember to check the patency of the nasal passages and for any

history of epistaxis.

Cormack and Lehane classification of glottic visualization

Clinical tests

These are used in an attempt to predict difficult laryngoscopy (i.e. Cormack and Lehane grades 3 and 4), which

occurs in approximately 1–;2% of the surgical population. Ideally, these tests should have a high specificity (the

ability to correctly identify normal patients as normal) and a high sensitivity (to detect true difficult intubations). No

single test can be used to predict difficult laryngoscopy with certainty. Combining two or more tests improves the

positive predictive value (the percentage of difficult laryngoscopies correctly predicted as difficult) and increases

the specificity, but decreases the sensitivity.

Prediction of difficult laryngoscopy is imprecise. The tests described have high specificities (that is they are good at

predicting when laryngoscopy will be easy). Since the same factors are involved in easy laryngoscopy and

successful airway maintenance with a mask (extension at the craniocervical junction and mandibular protrusion),

predicting easy laryngoscopy is also a prediction of successful control of the airway changes associated with

induction of anaesthesia. If several of the tests are positive the clinician should have a high index of suspicion that

direct laryngoscopy will be difficult and consider securing the airway before inducing anaesthesia.

Interincisor gap

Ask the patient to open their mouth as wide as possible.

Less than two finger breadths (3 cm) distance between the incisor teeth is associated with difficulty in

conventional laryngoscopy.

An interincisor gap of less than 3 cm reduced the prevalence of easy intubation from 95% to 62% in one

large series.

P.868

Protrusion of the mandible

Ask the patient to protrude their mandible. Look at the position of the lower teeth in relation to the upper

teeth.2 Classes B and C are associated with difficult laryngoscopy:

o Class A: the lower incisors can be protruded anterior to the upper incisors.

o Class B: the lower incisors can be brought ‘edge to edge’ with the upper incisors.

o Class C: the lower incisors cannot be brought ‘edge to edge’.

Mallampati test (Samsoon and Young modification)

Mallampati test (with Samsoon and Young's modification)3

Sit in front of the patient who should be sitting up with their head in the neutral position. Ask the patient to

open their mouth maximally and protrude their tongue without phonating. Note which of the following

structures are visible: (Fig. 37.2)

o Class 1: faucial pillars (palatoglossal and palatopharyngeal folds), soft palate, and uvula visible.

o Class 2: faucial pillars and soft palate visible. Uvula masked by base of tongue.

o Class 3: only soft palate visible.

o Class 4: soft palate not visible.

Class 3 and 4 views are associated with difficulty. When used in isolation the Mallampati test correctly

identifies about 50% of difficult intubations.

Flexion/extension at the craniocervical junction

This is best assessed by asking the patient to maximally flex their neck. The examiner's hand is then

placed on the back of the patient's neck to prevent movement of the cervical spine and the patient is

asked to nod their head. Alternatively a pen can be held against the forehead whilst maximally flexing and

extending the neck. Greater than 90° of movement should be possible. Reduced movements are

associated with difficult laryngoscopy.

The thyromental distance (Patil's test)4

The distance from the tip of the thyroid cartilage to the tip of the mandible, with the neck fully extended. This

should be greater than 6.5 cm (three finger breadths) and estimates the potential space into which the tongue can

be displaced on laryngoscopy. A distance of less than 6 cm is associated with difficult laryngoscopy and predicts

75% of difficult laryngoscopies.

The sternomental distance5

The distance from the upper border of the manubrium to the tip of the mandible with the neck fully extended. A

distance of less than 12.5 cm is associated with difficult laryngoscopy in adults.

Other tests

Radiographs of mandibular length and depth have been used to predict difficult intubation. These are time-

consuming and are probably no better than the above clinical tests.

With cervical spine disease (e.g. ankylosing spondylitis, rheumatoid arthritis, Klippel—Feil abnormality)

flexion/extension views are useful to determine the stability of the odontoid peg, the mobility of the

atlantoaxial—occipital complex and the presence of fracture dislocations. Patients with disease that

involves the atlantoaxial-occipito complex have a higher prevalence of difficult laryngoscopy than those

with disease below C2.6

Adults with a partially obstructed airway may, if time allows, be investigated with CT scanning. The scan

will show the site of the lesion, the dimensions of the trachea, the relationship of the lesion to the carina

and in the case of malignancies, whether or not the tracheal wall has been invaded.7

Successful airway management is dependent on careful patient assessment. If there is a high likelihood that mask

ventilation and/or direct laryngoscopy will be difficult, consideration should be given to securing the airway with the

patient awake.

Management of the obstructed airway

Management of patients with an obstructed airway

Each patient should be assessed to identify the level and nature of the obstruction. Broadly these can be divided

into:

Oropharyngeal problems (trauma, tumour, infection).

Lesions in and around the larynx (usually malignant or infective).

Mid tracheal obstruction (often secondary to retrosternal goitres).

Lower tracheal and bronchial obstruction (usually large mediastinal masses, e.g. lymphomas, thymomas,

and carcinomas).

A careful history will identify those patients in whom obstruction is severe. Stridor at rest implies a reduction of

airway diameter of at least 50%. In addition to noisy breathing, there may be a history of waking up at night in a

panic and sleeping upright in a chair.

Upper airway obstruction

Upper airway obstruction can be divided into two groups:

Intubation is likely to be straightforward (see airway assessment p. 866). These patients should have an

inhalational induction (see p. 879) in the operating theatre with the ENT surgeon gowned with a

tracheostomy tray and rigid ventilating bronchoscope close to hand. The patient may be intubated with a

tracheal tube or with a rigid ventilating bronchoscope. If the patient is impossible to intubate a

tracheostomy can be performed in the anaesthetized spontaneously breathing patient.

Intubation is expected to be difficult or impossible (extensive tumour, fixed hemilarynx, or gross anatomical

distortion). This may require preliminary tracheostomy under local anaesthetic. Helium may help

ameliorate stridor whilst the tracheostomy is performed. Heliox (premixed helium/oxygen) contains only

21% oxygen. The oxygen content may be increased by adapting rotameters to fit the Heliox cylinder, or

using a simple ‘Y’ connector and an oxygen cylinder.

Mid tracheal obstruction

Usually there is a history over several months. If time allows a CT scan should be performed to show the

site of the lesion, the dimensions of the trachea, the relationship of the lesion to the carina, and whether

the tracheal wall is invaded.

Remember that in these patients an emergency tracheostomy may not be an option since access to the

trachea may be compromised by the presence of a large neck mass. In some patients, it may be possible to

perform a tracheostomy but the tube may not be long enough to bypass the obstruction.

The most common cause of mid tracheal obstruction is a retrosternal goitre. In the majority of

cases visualization of the larynx is not difficult and tracheal intubation is easy. The site of

compression is of sufficient distance above the carina to accommodate both the tracheal cuff and

the bevel thus allowing conventional induction of anaesthesia.

If there is concern that conventional intubation will be difficult, awake fibreoptic intubation may be the

technique of choice. However, if the lumen of the trachea is very small passage of the fibreoptic scope and

tube may be unpleasant for the patient (the ‘cork in a bottle’ phenomenon). An experienced operator is

required.

Some patients with very marked tracheal obstruction may be best managed with an inhalational induction

and intubation with either a very small tracheal tube or a rigid bronchoscope.

Lower tracheal and bronchial obstruction

These are very difficult cases. Detailed discussion should take place and management be planned by experienced

specialists. Sudden respiratory obstruction can occur at any stage of the anaesthetic. Induction of anaesthesia can

alter the support of the bronchial tree so that collapse can occur with total respiratory obstruction:

Obtain tissue diagnosis if possible under local anaesthesia.

If superior vena caval obstruction is present, urgent ‘blind’ chemotherapy or radiotherapy may have to be

considered, even in the absence of a histological diagnosis.

The use of a rigid intubating bronchoscope to relieve the obstruction may be lifesaving.

Transfer to a unit where facilities for extracorporeal oxygenation are available may be necessary in some

cases.

Management of the unexpected difficult airway

Despite careful assessment, unexpected airway problems can occur. Approximately 50% of airway difficulties will

only become apparent after the induction of general anaesthesia. When a problem does arise, the first priority is to

decide whether the problem lies with difficult airway maintenance, difficult intubation or both:

If the main problem is intubation, but facemask ventilation is easy, a controlled stepwise approach can be

followed.

If the problem lies with facemask ventilation, then an airway emergency develops. Maintenance of patient

oxygenation becomes the priority.

Failed mask ventilation

Is the problem due to:

Failure to maintain upper airway patency (most common problem)?

Laryngospasm?

Laryngeal pathology?

Lower airway pathology?

Failure to maintain airway patency

100% oxygen should be used whenever an airway problem appears to be developing.

Triple-thrust manoeuvre–two hands are used to thrust the jaw forwards. An assistant should squeeze the

anaesthetic bag.

Oral and/or nasal airways may help.

Ensure that head positioning is optimal–‘sniffing the morning air’, a single pillow under the head only, neck

flexed, head extended.

If still unable to ventilate by facemask insert a laryngeal mask airway (LMA) or Combitube.

If cricoid pressure has been applied try releasing it carefully.

Cricothyroidotomy.

Laryngospasm

Apply 100% oxygen with the mask held tightly and the expiratory valve closed. Apply CPAP/PEEP and gently

attempt manual ventilation. Avoid excessive pressure as this may distend the stomach.

Deepening anaesthesia with an IV induction agent (particularly propofol) may reduce spasm, or consider a

small dose of suxamethonium (0.25–0.5 mg/kg).

As laryngospasm starts to ‘break’ anaesthesia should be deepened with a volatile agent or further doses of

intravenous agent as appropriate.

If laryngospasm is severe a full dose of suxamethonium (1.5 mg/kg) should be administered.

If there is no venous access suxamethonium may be administered intramuscularly or into the tongue (3

mg/kg).

P.873

Laryngeal pathology

Unexpected laryngeal pathology causing problems with mask ventilation is a very rare scenario. Cricothyroidotomy

may be lifesaving.

Lower airway pathology

Acute severe bronchospasm may present as difficulty in mask ventilation. This may present de novo or may

be part of an adverse drug reaction. The management of acute severe bronchospasm is discussed on p.

848.

Very rarely lower airway pathology due to diagnosed or undiagnosed mediastinal masses may present as

difficulty with ventilation at induction of anaesthesia. The use of a rigid bronchoscope to maintain airway

patency may be lifesaving.

Failed intubation

Defined as difficulty in viewing the larynx, causing failure to intubate the trachea. Remember that patients do not

die from failure to intubate but failure to oxygenate.

The clinical scenario determines the best management:

If the patient has a full stomach and is undergoing a rapid sequence induction then it is best to institute a

failed intubation drill early and wake the patient up. Rarely there are clinical situations (e.g. in obstetrics)

where you may decide to proceed with surgery under mask anaesthesia.

In an elective case, when the patient has received a full dose of a nondepolarizing muscle relaxant and

mask ventilation is easy, it may be appropriate to try a full range of techniques (see Fig. 37.3).

Possible strategies in a case of difficult intubation

Optimize the position of the head (flexion of the cervical spine with maximal extension at the craniocervical

junction).

Have different laryngoscope blades available. The McCoy blade with a flexing tip can be particularly helpful.

Manipulation of the larynx by the assistant.

Use a gum elastic bougie (‘Eschmann tracheal tube introducer (reusable)’, Sims Portex Ltd, New Portex

House, Military Road, Hythe, Kent CT21 5BN, UK, tel: 01303 260551). This is probably the most useful piece

of equipment for any unexpected difficult intubation. Keep the bougie well anterior to ensure it does not

enter the oesophagus, and in the midline to avoid right or left pyriform fossae. 90° counter clockwise

rotation of the tube aids successful railroading once the bougie is in position.

Consider alternative intubating techniques (intubating LMA, Combitube, fibreoptic scope, retrograde

methods).

With abnormal anatomy the cords may be difficult to see. Pressure on the chest may produce a bubble at

the laryngeal opening.

Diagnosis of misplacement

Retain a high index of suspicion after a difficult intubation.

Suspect oesophageal placement if you cannot confirm: normal breath sounds in both axillae and absent

sounds over the stomach; rise and fall of chest; normal ETCO2 trace; normal airway pressure cycle.

The trachea is a rigid structure, the oesophagus is not. If negative pressure is applied to the ETT, failure to

aspirate air (e.g. with a bladder syringe directly attached to the ETT) suggests oesophageal placement.

Confirm ETT placement with a fibreoptic scope.

Remember–if in doubt, pull it out and apply bag and mask ventilation.

The intubating laryngeal mask airway (ILMA)

Intubation via the laryngeal mask airway may be performed blind, aided by a fibrescope, or aided

via a variety of other methods (guidewire, bougie, lightwand).

The ILMA (Intavent) is a modification of the LMA designed to facilitate blind orotracheal intubation,

fibreoptic intubation, or in very cooperative patients awake intubation.

It features a rigid anatomically curved airway tube terminating in a standard 15 mm connector. It is fitted

with a rigid metal handle.

Unlike a standard laryngeal mask, it has a single epiglottic elevating bar replacing the two bars of a

standard LMA. The caudal end of the bar is not fixed to the mask floor allowing it to elevate the epiglottis

when an endotracheal tube is passed through the aperture.

It comes in three sizes:

o size 3 for a small adult or large child

o size 4 for a normal adult

o size 5 for a large adult.

All three sizes will accept a tube of up to 8 mm internal diameter.

It is designed to be used with a straight silicone wire-reinforced cuffed endotracheal tube not exceeding 8

mm internal diameter capable of being passed through the ILMA including the pilot balloon and pilot

balloon valve. The tube has an atraumatic tip to minimize the risk of pharyngeal trauma.

The tube may be passed into the trachea blindly or under direct vision using a suitable fibreoptic scope.

It is recommended that the ILMA is removed once the tube is passed into the trachea.

A stabilizing rod is available to keep the tracheal tube in place and slide the ILMA out of the mouth.

The Combitube

The Combitube™ (Sheridan Catheter Corporation) is an airway device that combines the functions of an

oesophageal obturator airway and a conventional endotracheal airway.

It has two lumens–an oesophageal with an open proximal end and a blocked distal end with perforations at

pharyngeal level and a tracheal with open proximal and distal ends.

It has two inflatable cuffs–a large proximal cuff (85 ml) inflated in the pharynx to seal off the oral and nasal

cavities and a smaller distal cuff (10 ml) to seal off the proximal oesophagus or trachea.

The small size is recommended for general use.

Insertion:

o With the head in the neutral position insert the Combitube blindly into the pharynx until the two

black rings are level with the teeth. A laryngoscope may be helpful.

o Inflate the large cuff (blue) with 85 ml of air. This may require considerable force. The Combitube

may ride up like a laryngeal mask.

o Inflate the distal cuff (white) with 10 ml of air.

o In 98% of cases the Combitube will be inserted into the oesophagus. First attach the breathing

system to the blue oesophageal lumen and confirm ventilation by auscultation and capnography.

o In 2% of cases the Combitube will have entered the trachea. If there is no air entry on connecting

the ventilation system to the blue lumen try the distal white lumen and confirm positioning by

auscultation and capnography.

Contraindications:

o Patients less than 5 feet (1.5 m) tall.

o Those with intact gag reflexes.

o Patients with oesophageal pathology–oesophageal perforation has been reported.

o Patients who have ingested caustic substances.

Retrograde intubation

Many different methods have been described, all based on the technique of Waters.8

The airway is anaesthetized as described. (For awake intubation).

A Tuohy needle is passed through the cricothyroid membrane. Correct positioning is confirmed by the

aspiration of air.

A guidewire is passed via the Tuohy needle and retrieved from the nose or mouth.

An introducer is passed over the guidewire–a 16G ureteric dilator fits over a 145 cm 0.038 in Amplatz Super

Stiff guidewire and is a snug fit for a 6.0 mm flexometallic tube.

The tube is passed over the guidewire and introducer until it arrests against the guidewire protruding

through the posterior surface of the cricothyroid membrane.

The guidewire and introducer are withdrawn from above whilst applying forward pressure on the tube.

Correct tube placement is confirmed in the usual way.

An alternative technique involves threading the guidewire through the suction port of the fibrescope and

using the wire to guide the fibresope into the trachea.

Cook (UK) make a commercially available retrograde intubation kit for use with endotracheal tubes of

internal diameter 5 mm or larger.

Needle cricothyroidotomy

In the can't intubate, can't ventilate scenario emergency tracheal access may be required. Needle

cricothyroidotomy is quicker and easier than formal tracheostomy. It is performed percutaneously with either a

large (less than 2 mm IV intravenous cannula or with a larger (greater than 2 mm ID) specifically designed cannula.

Intravenous cannula

A 14G cannula attached to a 10 ml syringe is inserted through the cricothyroid membrane in the midline at

an angle of 30–45°.

Air is aspirated to confirm placement and the catheter advanced into the trachea.

Oxygen may be from a jet injector (flow rate through a 14G cannula 800 ml/s), a flow regulator at 15

litre/min (flow rate through a 14G cannula 400 ml/s), anaesthetic machine oxygen flush at 32 kPa (flow rate

through a 14G cannula 200 ml/s), or anaesthetic bag at 60 cmH 2O (flow rate through a 14G cannula 80

ml/s).

Complications include kinking, surgical emphysema, and problems with exhalation.

Formal cricothyroidotomy kit

Examples are the Melker or Patil cricothyroidotomy sets (Cook UK Limited, Monroe House, Letchworth,

Herts SG6 1LN, UK).

A guidewire is passed into the trachea via a needle inserted into the cricothyroid membrane.

A cannula is passed into the trachea over a dilator.

Ventilation is via the anaesthetic circuit or a Sanders type injector–most cannulas have both standard (15

mm connector) and Luer lock connectors.

Complications include pneumothorax, surgical emphysema, and bleeding.

It is important to make sure there is no obstruction to expiration otherwise barotrauma may result.

Extubation of the patient who has been difficult to

intubate

Following multiple attempts at intubation the airway may be oedematous and bloody. On occasions, an elective

tracheostomy may be necessary.

Optimize the patient's medical condition:

o Aspirate secretions, administer bronchodilators.

o Ensure normovolaemia. Attenuate the cardiovascular stress effects of extubation. Esmolol may be

useful.

o Minimize stomach contents if possible.

o Can airway oedema be minimized? Position the patient head up. Consider the use of intravenous

dexamethasone or nebulized adrenaline.

o Ensure there is no residual muscular paralysis.

Optimize position for extubation:

o Consider sitting the patient up to maximize the FRC and minimize airway obstruction.

Aids to extubation:

o Consider extubation over a jet stylet (Cook airway exchange catheter), a nasogastric tube, or a

fibreoptic scope through which oxygen can be supplied.

o Consider a tongue stitch to pull the tongue forward if obstruction with the tongue is likely to be a

problem

o A nasal airway (or cut nasotracheal tube) may help prevent obstruction.

Have a back up plan:

o LMA

o Combitube

o cricothyroidotomy.

Inhalational induction

Common indications for inhalationl induction include:

babies and young children

needle phobic adults

acute upper airway obstruction due to lesions in and around the larynx, e.g. acute epiglottitis, perilaryngeal

tumours

bronchopleural fistula

no easily accessible veins.

If possible explain the procedure to the patient at the preoperative visit.

Masks with integral teets are useful in babies who are still suckling. In older children use of a cupped hand around

the fresh gas delivery tube is used. Halothane or sevoflurane are the induction agents of choice to permit smooth

induction of anaesthesia. For patients with airway obstruction 100% oxygen is used, otherwise 50% nitrous oxide in

oxygen is satisfactory. When using halothane the initial inspired concentration should be 1% and increased in 0.5%

increments until surgical anaesthesia is established (small central pupils and a reduction in blood pressure).

Sevoflurane can be introduced at 4–8%.

In cooperative patients a single breath induction technique can be used. A 4 litre bag (or two 2 litre bags in series)

is prefilled with halothane 5% or sevoflurane 8% in oxygen. The patient exhales fully and then takes a single vital

capacity breath and is encouraged to breath hold for as long as possible. Smooth induction may be achieved within

30–60 s.

Difficulties with inhalational induction

Slow induction of anaesthesia. Patients with stridor have low alveolar minute volumes. Induction of

anaesthesia and deepening of the anaesthetic will be slow. Sevoflurane may fail to provide anaesthesia of

sufficient depth to allow instrumentation of the airway. Adequate depth of anaesthesia is usually evidenced

by a decrease in blood pressure and small central pupils. A change to halothane may be worthwhile.

With stridor maintain CPAP during induction.

Occasionally airway obstruction may be so severe that gas induction is not possible. Consider tracheostomy

under local anaesthetic.

Airway problems may occur in stage 2 of anaesthesia (excitation) immediately after the patient loses

consciousness. Attempt chin lift and jaw thrust. Insertion of an oral airway can induce coughing and

laryngospasm. Consider the use of a nasal airway in these circumstances.

Laryngospasm.

Rapid sequence induction

Rapid sequence induction is employed in the patient with a full stomach who requires general anaesthesia. The

concept is loss of consciousness followed by intubation in the presence of cricoid pressure, without facemask

ventilation. If intubation fails the drugs should wear off rapidly and the patient restart spontaneous ventilation

before hypoxia intervenes.

Meticulous assessment of the airway is mandatory preoperatively to look for likely difficulties with tracheal

intubation. If preoperative evaluation suggests a problem with intubation, consider alternative techniques such as

surgery under local or regional anaesthesia or awake fibreoptic intubation.

The anaesthetist must have a management plan should intubation fail (see p. 874).

Technique

Check the anaesthetic machine, laryngoscopes, and tracheal tubes.

The patient must be on a tipping trolley.

Attach appropriate monitoring devices.

Position the patient's head as if ‘sniffing the morning air’ (one pillow under the head, cervical spine flexed

with extension at the craniocervical junction).

At least one skilled assistant is needed to perform cricoid pressure.

Suction apparatus is switched on and passed under the patient's pillow to the anaesthetist's right hand.

Preoxygenate with 100% oxygen for 3–5 min (or four vital capacity breaths with high flow into the circuit in

emergencies).

Administer a sleep dose of intravenous induction agent (thiopental 2–5 mg/kg, etomidate 0.2–0.3 mg/kg,

propofol 1–2 mg/kg) followed immediately by 1.5 mg/kg of suxamethonium.

Apply cricoid pressure as soon as consciousness is lost.

Intubate as soon as the patient relaxes.

Maintain cricoid pressure until the tracheal cuff is inflated and correct placement of the tube is confirmed

by capnography and auscultation of the lungs.

The main problem with rapid sequence induction is haemodynamic instability. Excessive doses of induction agent

may result in circulatory collapse (especially if the patient is hypovolaemic), whereas an inadequate dose may

result in tachycardia and hypertension.

Special considerations

Thorough preoxygenation is essential. The mask must be close fitting and the reservoir bag moving. Any

entrainment of air during preoxygenation negates the whole process. Start again.

Inject drugs into a rapidly running saline infusion through a large cannula.

In patients who will not tolerate preoxygenation (e.g. distressed children) consider gentle IPPV

after injection of drugs.

With patients in whom hypertension and tachycardia is undesirable (e.g. ischaemia/hypertension) consider

alfentanil 10 µg/kg 1 min prior to induction and following preoxygenation. In the event of intubation failure

this may be reversed with naloxone (400 µg IV).

Correct application of cricoid pressure

The technique of cricoid pressure to prevent regurgitated material entering the pharynx was described by Sellick. 9

This simple manoeuvre must be applied correctly as incorrect application can cause difficulties.

The cricoid cartilage is held between the thumb and middle finger and pressure is exerted mainly with the index

finger. Some authors recommend a bimanual technique with the second hand behind the neck. A minimum force of

30 N is required. Correctly applied, cricoid pressure should allow facemask ventilation without risk of gastric

distension, but airway obstruction is possible, particularly when applied with a poor technique.

Awake fibreoptic intubation

Indications for awake fibreoptic intubation

Known or suspected difficult intubation.

Known or suspected cervical cord injury.

Morbid obesity.

A patient with full stomach in whom a difficult intubation is anticipated.

Contraindications to awake fibreoptic intubation

The uncooperative patient.

Haemorrhage in the upper airway.

Severe stridor secondary to perilaryngeal tumour.

Allergy to local anaesthetics.

The degree of psychological and physical disturbance to a patient depends on the experience of the operator and

their lightness of touch. The technique is easily mastered with practice. Pharyngeal and laryngeal reflexes are

obtunded by local anaesthetic agents. With judicious sedation intubation can be achieved with little discomfort to

the patient.

Equipment

The fibreoptic scope must be sterilized appropriately beforehand.

The light source must be checked and the fibrescope prefocused on printed material.

The tip should be defogged with a commercial solution.

The fibrescope should be lubricated along its length with a water-soluble lubricant.

The suction port should be checked to ensure that it is patent and the connections are airtight.

The patient should be monitored with ECG, non-invasive blood pressure measurement, and pulse oximetry.

Assistance

Skilled assistance from an operating department assistant or anaesthetic nurse is mandatory.

Preparation of the patient

A comprehensive preoperative assessment of the patient's airway must be made. While the nature and site

of the proposed surgery usually dictate the route for intubation, consider simple facts like nostril patency

and limitation of mouth opening before making the decision.

Explain the indication to the patient, emphasizing the primary consideration of safety.

Administer an antisialogogue (intramuscular glycopyrrolate 200 µg 1 h prior to intubation). This improves

the view by decreasing secretions and enhances the action of topical local anaesthetics.

Apply monitoring and obtain intravenous access. Administer supplemental oxygen to all patients

via a nasal catheter.

Sedate the patient judiciously with a combination of narcotics and benzodiazepine. Narcotics give mild

sedation, analgesia, and are antitussive. Fentanyl (25 µg increments to a maximum of 1 µg/kg) is suitable.

Naloxone should be available to reverse narcotic-induced respiratory depression. Benzodiazepines produce

amnesia and sedation–midazolam (0.5–1 mg increments) until sedated but maintaining verbal contact.

Flumazenil should be available. Over-sedation is a common error and should be avoided at all costs.

Position of the patient

Sit the patient up with the operator in front. This prevents the tongue and pharynx collapsing backwards and

obstructing the view. It also prevents any secretions pooling at the back of the oropharynx. It is, however,

confusing for beginners who are used to viewing the anatomy from the head of the patient. Otherwise stand in the

normal intubating position with the patient supine.

Nasal route

The route of choice if available, but the passage of a nasal tube is always uncomfortable.

Contraindications to the nasal route include bleeding diathesis, an anticoagulated patient, severe intranasal

disease, basal skull fracture, or a CSF leak.

Advantages include ideal positioning to see the larynx, no gagging, no biting, and less interference with the

tongue.

Local anaesthesia of the nose must be accompanied by vasoconstriction. Conventionally 10% cocaine

solution is used, but some worry about coronary vasoconstriction. 4% lidocaine (lignocaine) 3 ml and 1%

phenylephrine 1 ml is a useful alternative.

Dilate the nostrils to the anticipated size of the endotracheal tube to be used with warmed nasal airways

lubricated with lidocaine (lignocaine) jelly.

The posterior third of the tongue and oropharynx should be anaesthetized with five to ten sprays from a

metered dose 10% lidocaine (lignocaine) spray. Each spray contains 10 mg lidocaine (lignocaine).

Alternatively 2 ml 4% lidocaine (lignocaine) can be sprayed onto the back of the pharynx via the nasal

airway.

Anaesthesia below the cords is accomplished by puncture of the cricothyroid membrane with a 22G cannula

with the neck in extension. Correct positioning is confirmed by the ability to easily aspirate air. 2 ml 4%

lidocaine (lignocaine) is injected at end expiration. Coughing spreads the local anaesthetic above and below

the vocal cords. Absolute contraindications are a coagulopathy and local tumour. Relative contraindications

are an unstable cervical spine, when neck extension is undesirable, and morbid obesity, when identification

of the anatomical landmarks is difficult.

Nebulized 4% lidocaine (lignocaine) 4 ml plus 1% phenylephrine 1 ml is a useful alternative. This is

administered using a standard oxygen-driven nebulizer with a flow rate of 8 litre/min and the

patient in the sitting position. The patient is asked to breathe through the nose and a standard

facemask is used (it may still be necessary to anaesthetize the larynx and trachea via the suction

port of the fibreoptic scope as described below). This method has the advantage of minimal

patient disturbance and no requirement for identification of anatomical structures. It can be used

in the patient with an unstable cervical spine.

An alternative to a cricothyroid puncture is to inject lidocaine (lignocaine) via the suction port of the

fibrescope. 4% lidocaine (lignocaine) 2 ml is sprayed onto the vocal cords and a further 2 ml is injected

down the trachea once the tip of the fibrescope has been manoeuvred between the cords.

Superior laryngeal nerve blocks are advocated by some, but in practice are not usually necessary. The

superior laryngeal nerves convey sensation from the inferior aspect of the epiglottis and the laryngeal inlet

above the vocal cords. They may be anaesthetized by applying pledgets soaked in 4% lidocaine

(lignocaine) into each pyriform fossa with Krause's forceps for 2 min. Alternatively, in patients who have

limited mouth opening, the nerves may be anaesthetized by injecting 2–3 ml of local anaesthetic bilaterally,

deep to the thyrohyoid membrane, just above the thyroid cartilage at a point onethird of the distance

between the midline and the tip of the superior cornu.

Oral route

This route is more difficult because the fibrescope is not anatomically directed towards the glottis.

An endoscopic oral airway or bite block should be used to protect the fibrescope. The endoscopic oral

airway has the advantage of preventing dorsal displacement of the tongue and keeping the instrument in

the midline. Such devices include the Berman airway (Vital Signs Inc.) and the Ovassapian airway (Kendall).

The mouth can be anaesthetized with 10% lidocaine (lignocaine) spray to the tongue and oropharynx as

described above. Alternatively nebulized 4% lidocaine (lignocaine) can be administered via a standard

nebulizer mouthpiec with the nose occluded.

Laryngeal and tracheobronchial anaesthesia is obtained with cricothyroid puncture, or instillation of

lidocaine (lignocaine) through the suction port of the fibrescope as described above.

Passing the endotracheal tube

Stand at the head or in front of the patient as a matter of personal preference. The control section of the

fibrescope is held in the dominant hand with the thumb positioned on the angle control and the index finger

on the suction port. The light source should be to the operator's left. If available a camera and monitor

should be used. The fibrescope should be held fully extended with the other hand. A suitably sized,

reinforced endotracheal tube should be mounted on the fibrescope. This can be prewarmed to soften it.

If the nasal route is chosen the fibrescope is advanced 15 cm into the pharynx. If the oral route is used it

should be advanced 8–10 cm.

If in the midline the vocal cords will come into view as the tip is flexed slightly upwards.

Rotation of the fibrescope about its long axis may be required to bring the tip into the midline.

The first view after the fibrescope is advanced through the vocal cords will be the thyroid cartilage. The tip

is straightened or returned to the neutral position and the instrument advanced until the tracheal cartilages

and finally the carina is seen.

The endotracheal tube is threaded over the fibrescope and into the trachea. The bevel should face

backwards.

Correct positioning above the carina is confirmed visually. The presence of carbon dioxide in the expired

gas confirms tracheal placement. Avoid cuff inflation until the last moment as the increased resistance to

breathing may panic some patients.

Difficulties

Can't get a good view

Always think ‘where am I, what am I looking at?’.

The most common problem is that the tip of the fibrescope is in one of the pyriform fossae and not in the

midline. Try rotating the scope to centralize the tip or pull back until recognizable structures appear.

Dimming the lights to see where the tip of the fibrescope transilluminates tissues of the neck is sometimes

useful. The light is visible, deviated laterally or invisible. If the light is invisible the tip of the scope is either

not sufficiently far advanced or is in the oesophagus.

Excess secretions may obscure anatomical landmarks. Try using the suction port or alternatively insufflate

oxygen down it (2 litre/min). If this does not work remove the scope and try to clear secretions with a

sucker or dry swab.

If the tongue base is against the posterior pharyngeal wall ask the patient to protrude their tongue.

Problems with passage of the endotracheal tube

Sometimes it is easy to intubate the trachea with the scope, but the endotracheal tube cannot be

railroaded into the trachea.

Protrusion of the tongue, maximum inspiratory efforts, tube rotation, changing the axis of the airway, and

external laryngeal manipulation are all worth trying.

It may be necessary to use a smaller endotracheal tube.

Awake intubation in the presence of a full stomach

Patients at risk of aspiration of stomach contents must be approached with common sense. Clearly the

nose, mouth, and oropharynx can safely be anaesthetized.

Some anaesthetists worry that anaesthesia of the larynx and tracheobronchial tree may suppress

protective airway reflexes to unacceptable levels. Others believe that a lightly sedated patient can respond

to a threat to the airway from vomiting or regurgitation, and clear it by turning and coughing, retching, or

swallowing repeatedly. There are published reports of the safety of awake intubation in the presence of a

full stomach.10

Apnoeic oxygenation

John Lehane

Interruption of ventilation may precipitate catastrophic hypoxaemia. This can be delayed or prevented by the

correct use of oxygen. A detailed understanding of the mechanisms pertinent to apnoeic oxygenation is vital.

Apnoea whilst breathing air

Resting oxygen consumption is 250–300 ml/min in a typical adult.

At the onset of apnoea the oxygen available to support vital organ function is almost entirely that stored in

the alveoli (about 200 ml) and that combined with haemoglobin (about 800 ml).

After 2 min, about half this store will be exhausted and the alveolar (PAO2) and arterial (PaO2) partial

pressures of oxygen will be less than 4 kPa.

By contrast, because CO2 is very soluble and well buffered in the body, the alveolar (PACO2) and arterial

(PaCO2) partial pressures of carbon dioxide rise slowly such that at 2 min the PaCO2/PACO2 will be about 6.6

kPa.

Within 4 min, hypoxaemia will cause cardiac arrest or severe brain injury whilst the change in PaCO2/PACO2

remains clinically unimportant.

Apnoea whilst breathing 100% oxygen

After breathing 100% oxygen the only gases present in the alveoli are oxygen, carbon dioxide, and water

vapour.

Total alveolar pressure is 100 kPa (1 atmosphere). This comprises water vapour (6 kPa), carbon dioxide (5

kPa), and oxygen (89 kPa).

After 2 min of apnoea PaCO2 will have risen to about 6.6 kPa, and PaO2/PAO2 decreased to 87.4 kPa.

After 30 min of apnoea PACO2 will have risen to about 15 kPa and PaO2/PAO2 decreased only to 79 kPa.

At the start of apnoea the oxygen stored in alveoli and blood is only about 2.4 litres. Over 30 min of apnoea

oxygen consumption is 7–9 litres. The required oxygen enters the body from the breathing system by

convective flow (see below).

By 30 min there is a severe respiratory acidosis but without hypoxia. Buffering the pH change with

intravenous trihydroxymethylaminomethane (THAM) will further extend survival. Sodium bicarbonate is

ineffective, serving only to increase PaCO2 during apnoea.

This process of preventing hypoxaemia is known as apnoeic oxygenation.

Convective flow

During ventilation, carbon dioxide enters alveoli at the same rate it is produced (about 250 ml/min).

However, during apnoea most of the carbon dioxide produced is buffered within the body and only about 5

ml/min enters the alveoli.

Oxygen continues to be absorbed from the alveoli at a rate of 250 ml/min resulting in a net loss of volume

and a fall in alveolar pressure.

This pressure drop causes convective gas flow (not diffusion) through the conducting airways to the alveoli.

Provided the patient's airway remains patent and connected to an oxygen supply then oxygen will be

passively drawn down the airway at a rate of about 245 ml/min.

Airway obstruction

Should the airway become obstructed then no gas will flow into the alveoli as oxygen is absorbed and lung

volume will, therefore, decrease by 245 ml/min.

The reduction in lung volume will lead to alveolar collapse (absorption atelectasis). This will cause

intrapulmonary shunting and arterial hypoxaemia.

By the time that one-third of alveolar volume is lost (2–3 min) the shunt fraction will have risen above 50%

and hypoxaemia will be severe.

Air entrainment

Should the patient be disconnected from the oxygen source whilst apnoeic, for example if the face mask is

removed to permit laryngoscopy, then room air instead of oxygen is drawn down the trachea at the same

rate of about 245 ml/min. In about 30 s nitrogen will start to enter the alveoli.

Since the rate of extraction of oxygen from an alveolus is determined by its perfusion, air (with its nitrogen)

is directed preferentially to the betterperfused (dependent) alveoli.

Oxygen will be rapidly diluted in these alveoli and the time to significant hypoxaemia may now be as little

as 2–3 min.

This is still substantially better than if the patient had not been preoxygenated at all.

Practical application

These considerations explain why, with careful use of oxygen and attention to airway patency, it is often possible to

allow for an extended period of apnoea without consequent hypoxaemia. In contrast, loss of airway control or

failure to maintain oxygen supply may rapidly precipitate a hypoxaemic crisis.

Changes in alveolar gas composition during extended periods of apnoea

  Period of apnoea

0 min 2 min 4 min 15 min 30 min 60 min

After breathing air:

PAO2 (kPa) 12 3.8 <0.5 – – –

PACO2 (kPa) 5 6.6 7.2 – – –

After breathing 100% oxygen:

PAO2 (kPa) 89 87.4 86.8 83.5 79 70

PACO2 (kPa) 5 6.6 7.2 10.5 15 24