fibre-optic intubation, including local anaesthesia for awake intubation

DENTAL AND MAXILLOFACIAL

© 2005 The Medicine Publishing Company Ltd273ANAESTHESIA AND INTENSIVE CARE MEDICINE 6:8

Airway problems are a major concern to anaesthetists. They commonly lead to minor morbidity such as dental damage and occasionally to more serious consequences including brain damage or death. Murphy performed the first fibre-optic intubation over 35 years ago using a choledochoscope. Five years later, Taylor and Towey described a series of airway problems managed by fibre-optic intubation under local anaesthetic. The introduction of fibre-optic intubation and awake fibre-optic intubation has revolutionized the anaesthetic management of the difficult airway. To perform fibre-optic intubation it is essential to have a basic understanding of the equipment, how to use it and how to prepare and maintain the airway for endoscopy.

The endoscope

Fibre bundles – an image is conducted from the distal tip of the endoscope (Figure 1) to the eyepiece by a bundle of fine glass filaments less than 1 mm in diameter. Each individual filament is less than 8 microns across. Fibre bundles are tightly bound only

Fibre-optic intubation, including local anaesthesia for awake intubationNick Woodall

Nick Woodall is Consultant Anaesthetist at the Norfolk and Norwich

University Hospital, UK. He qualified from Liverpool Medical School

and trained in anaesthesia in the North West, London, and the USA. His

clinical and research interests include airway problems and teaching

airway management.

at each end, which enables them to maintain their flexibility. It is essential that each filament retains precisely the same orientation to all the other fibres at either end of the bundle (coherence). If this were not the case, the viewed image would be scrambled and unrecognizable. Insertion tube – the optical fibres are encased in a layered steel insertion tube coated with a durable plastic outer layer. This robust construction protects the delicate fibres and ensures that rotation of the control section is directly transmitted to the distal tip. Bending section – active tip movement here is produced by the angulation control lever. Suction/instillation – fibre-optic laryngoscopes usually contain a single channel for suction or instillation of local anaesthetic. An epidural catheter inserted via the suction port may be used to direct a fine spray of local anaesthestic to the airway without loss of view. Videoscopes – a charge couple device at the distal tip transmits an image to a camera and display system. These instruments contain no optical fibres.

General principles of cleaningEndoscopes require cleaning, disinfection and leak testing before use. Flexible fibre-optic instruments are damaged by exposure to temperatures suitable for thermal disinfection. Therefore, chemical disinfection must be performed. Glutaraldehyde is hazardous to health and difficult to obtain; peracetic acid is a commonly used alternative. Manual cleaning should include a wash, brush and flush of the instrument and the working channels. Secretions must be cleared before they become hardened and impair the effectiveness of chemical disinfectants. Small cracks can develop in the soft, latex-free, rubber, protec-tive layer surrounding the bending section. A leak test confirms the integrity of the outer sheath, and ensures the endoscope is watertight. To perform a leak test, the venting connector is attached to the air-pump output socket, found as an integral part of some light sources. Expansion of the rubber covering of the bending section due to increased internal pressure should be observed. The entire instrument is then immersed in water, and observed

1

The endoscope

Suction port

Eyepiece

Focusing knob

Angulation control lever

Control section

Venting connector

Detachable light lead

Bending section

Distal end

Light guide

Insertion tube



for 30 seconds. The angulation control lever is then flexed to the maximum upwards and downwards positions. Escape of gas bub-bles indicates a leak and sterility cannot be guaranteed. It is essential to prevent environmental re-contamination of disinfected endoscopes by careful storage and handling before use.

Practical endoscopy technique

Effective endoscopy requires: • a good view• skilful manipulation of the instrument • familiarity with airway anatomy (see page 253).

Optimal view Patent airway – it is possible to use an endoscope effectively only in a cavity. During laparoscopy or colonoscopy, a cavity is distended by insufflation of gas. The airway cannot easily be distended and furthermore the airway cavity is narrow, therefore the endoscopist must aim to keep the endoscope tip centred in the airspace. White-out – when the instrument tip lies close to the mucosa or secretions, the intense light from the light source is reflected directly into the objective lens producing a white-out. This is inevi-table at the site of an obstruction when the advancing endoscope comes into direct contact with opposing mucosal surfaces. During general anaesthesia, airway obstruction commonly occurs. Airway patency must be restored to permit endoscopy. Head extension, jaw thrust and anterior traction of the tongue with a swab may be required (Figure 2). Conscious patients may be asked to protrude their tongue or breathe through their nose, thus opening the airway and increasing the space for endoscopy. Tumours or oedema may obstruct the airway. If attempts to open the airway fail, it may be necessary to search for a passage round the obstruction or to slide the endoscope gently, but blindly, between the two opposing mucosal surfaces, in the expectation that the tip will emerge into a cavity. This form of blind endoscopy may result in bleeding. Secretions – sputum or saliva smeared across the distal lens produces a blurred image. Systemic pre-treatment with an anti-cholinergic agent reduces the volume of secretions. Saliva may be cleared by gently flexing the tip of the endoscope against the

mucosa, or by asking the patient to cough or swallow. It is often necessary to remove the endoscope and clean the tip with a swab. Small volumes or discrete collections of sputum may be bypassed by manipulating the instrument round them. The suction ports of fibre-optic laryngoscopes are narrow. Thick secretions are most effectively cleared from the upper airway with a Yankeur sucker or suction catheter passed gently through the mouth or nose. Bleeding is best prevented by topical vasoconstrictors and care-ful endoscopy technique. Once bleeding has occurred it should be managed in the same way as secretions. Fogging – condensation may be prevented by warming the endoscope tip or may be removed by asking the patient to take a slow deep breath.

ManipulationWhen manipulating a fibre-optic laryngoscope there are few options. It may be inserted or removed, rotated to the left or right, or the tip may be flexed or extended.

Insertion: the instrument is best inserted under endoscopic view, in the line of the airway. For nasal intubation, follow the floor of the nose backwards, through the space under the inferior turbinate until the soft palate, then pharynx and larynx come into view. For oral intubation follow the mucosa of the tongue. If recognizable structures are not seen, withdraw until they become visible. If necessary, start again after cleaning the lenses and checking the focus.

Flexion and extension: downward movement of the angulation control lever with the thumb elevates the tip of the instrument, directing it towards the upper field of view. Elevation of the control lever moves the tip towards the lower field of view. Flexion takes place along a line between the notch (seen through the eyepiece) and the centre of the field.

Rotation: active tip movement occurs in one plane, therefore sideways movement must be achieved by rotating the control section around its long axis. For rotation to be transmitted to the endoscope tip, the insertion tube must be held straight, with slight tension between the two hands (Figure 3). If redundant loops of insertion tube develop between the hands of the endoscopist the tip tends to drift and will fail to respond as the control section is rotated. This very important point is often neglected.

Steering the instrument through the airway requires all three components before advancement. The control section is rotated until the notch is directly in line with the objective, the tip of the instrument is flexed to the point where the objective appears at the centre of the field, the insertion tube is then advanced in this line. To keep the objective close to the centre of the field of view, small frequent corrections are required.

Awake fibre-optic intubation

Preparation Patients require an explanation of the indication for awake intuba-tion and a description of what they should expect (Figure 4). Topical nasal vasoconstrictors (e.g. xylometazoline spray or cocaine) reduce bleeding where nasotracheal intubation is planned. Anti-

2 Tongue traction may be combined with jaw thrust and head extension

to provide airway patency.



cholinergic agents reduce secretions and increase the intensity, speed of onset and duration of topical local anaesthesia. Intra-venous glycopyrrolate, 5 µg/kg, is effective if given 10–15 min before administration of local anaesthetic. Light sedation is helpful for anxious patients but patient cooperation is essential and over-sedation is a dangerous substitute for adequate local anaesthesia.

Local anaesthesia of the airwayNasal anaesthesia: cocaine (4–5%) is a commonly used topi-cal local anaesthetic for the nasal mucosa because it is also a vasoconstrictor. Unfortunately, myocardial ischaemia has been reported following small doses. The maximum recommended dose of cocaine is 1.5 mg/kg. Lidocaine 5% combined with phenylephrine is a highly acceptable substitute. Alternatively, 4% lidocaine, 2 ml, 80 mg, applied to the nasal mucosa as a spray or on cotton-wool-tipped swabs produces satisfactory analgesia of reasonable duration.

Oral analgesia: 4% lidocaine spray, 2 ml, 80 mg, is also suitable for oral intubation. The patient should swirl it around the mouth and then gargle with it. The gag reflex may be initiated by stretch receptors in the tissues of the oropharynx or by mucosal stimula-tion, therefore complete abolition is difficult with surface anaes-thesia alone. However, additional 10% lidocaine spray, 100 mg directed into the posterior oropharynx at the back of the tongue to the left, right and in the mid-line, usually provides good con-ditions for fibre-optic endoscopy or even laryngeal mask airway (LMA) insertion.

Warning: 10% lidocaine stings when applied to mucous mem-branes, therefore a dilute local anaesthetic solution should be applied first.

Anaesthesia of the lower airwayTopical anaesthesia of the lower airway may be used alone or supplemented with nerve blockade.

Spray-as-you-go: following topical anaesthesia of the mouth or nose, the endoscope is advanced into either orifice until the

posterior aspect of the tongue or the epiglottis can be seen. From a distance, 1 ml aliquots of local anaesthetic (4% lidocaine) are administered through the working port of the endoscope, first towards the back of the tongue. If the epiglottis is not seen, the endoscope is advanced further until it is visible overlying the glottis. The epiglottis and glottis are then sprayed in turn until the vocal cords cease reacting to local anaesthetic administration. The endoscope is then advanced closer to the larynx and additional local anaesthetic is delivered between the vocal cords until cough-ing ceases. Subsequently, the passage of an endoscope into the trachea through the mouth or nose is usually well tolerated. Large doses of lidocaine are needed for spray-as-you-go anaes-thesia. Much of the local anaesthetic is swallowed, absorbed and then metabolized in the liver before reaching the systemic circulation. The British Thoracic Society recommends an upper dose limit of 8.2 mg/kg for fibre-optic bronchoscopy with topical lidocaine.

Translaryngeal or transtracheal administrationDirect injection of local anaesthetic into the airway precipitates coughing, thus dispersing the local anaesthetic. This provides tracheal anaesthesia and also a significant degree of anaesthesia of the laryngeal inlet and epiglottis. The cricothyroid membrane is most easily located and recog-nized. Infiltration of the skin and subcutaneous tissues with local anaesthetic containing a vasoconstrictor provides analgesia and reduces bleeding at the puncture site. A cannula or needle is then inserted through the anaesthetized area into the airway. During insertion, this should be directed backwards and slightly caudad to avoid vocal cord trauma. Entry into the airway is confirmed by aspiration of air via the needle. Lidocaine 4%, 2–4 ml, 80–160 mg, is then rapidly injected and the needle removed. Injection at end inspiration results in the rapid upward spread of lidocaine whereas injection at end expiration produces more effective anaesthesia of the lower airway. Complications of cricothyroid puncture include broken needles, infected puncture sites and haematoma formation. These are uncommon but, as with other local anaesthetic injections, local infection or the presence of a coagulopathy may contraindicate its use.

NebulizationThe simplicity of nebulizing local anaesthetic to produce airway anaesthesia is attractive. Only about 8–12% of a nebulized drug

Patient preparation for awake fibre-optic intubation

• Explanation

• Nasal vasoconstrictors

• Anticholinergics

• Intravenous access

• Oxygen

• Monitoring

• Sedation

4

3 For rotation to be transmitted to the endoscope tip, the insertion tube

must be held straight, with slight tension between the two hands.



reaches the airway, therefore concentrated local anaesthesic solu-tions are needed in high doses. 10% lidocaine, 6 mg/kg, is reported to be effective. Following nebulization of this dose, peak plasma lidocaine concentrations have been found to be less than one-fifth of the level regarded as toxic (5 mg/litre). Nebulization is time consuming and the resultant airway anaesthesia often requires supplementation. This technique may be useful to obtund airway reflexes before some other form of local anaesthesia, if coughing needs to be avoided or minimized.

Nerve blocks Nerve blocks produce intense analgesia of part of the airway but are seldom needed for awake intubation. Limited mouth opening or restricted neck movement is common in patients with airway problems and these factors make nerve blocks more difficult.

Fibre-optic intubation under general anaesthesia

General anaesthesia is commonly used for the routine mainte-nance of endoscopy skills or in the management of uncooperative patients. In the presence of stridor, the application of topical local anaesthetic may precipitate acute airway obstruction, therefore intubation is usually performed under general anaesthesia in patients with severe upper airway obstruction.

Preparation: as with intubation under local anaesthetic, oxygen in high concentrations reduces episodes of hypoxia, antisialogogues reduce secretions, and nasal vasoconstrictors reduce bleeding from the nose. Consideration must be given to the selection of the anaesthetic technique, mode of ventilation, and maintenance of airway patency, additional airway adjuncts may also be used. There should be a back-up plan for ventilation if complete airway obstruction develops.

General anaesthesia: volatile agents or total intravenous anaes-thesia (TIVA) are suitable techniques. TIVA enables endoscopy to proceed without frequent interruptions to deepen anaesthesia with anaesthetic gases, provided the patient remains well oxy-genated.

Ventilation/oxygenation: there are several options for ventilation. Spontaneous ventilation with intubation at deep levels of

anaesthesia is very useful when dealing with cases of airway obstruction. In these situations, continuous positive-pressure ventilation (CPAP) is helpful because it may produce partial relief of airway obstruction. Helium is also worth consideration. Intermittent positive-pressure ventilation by face mask – in straightforward cases, muscle relaxants afford good intubating conditions, provided airway patency is maintained. It is important to check that ventilation is possible before administering a long-acting neuromuscular blocking agent. Transtracheal jet ventilation – purpose-built transtracheal can-nulae may be inserted before induction, under local anaesthetic, or later, following loss of consciousness (see Anaesthesia and Intensive Care Medicine 6:7: 237). Transtracheal jet ventilation requires a high-pressure oxygen source (e.g. Sanders injector) and a cannula of adequate size (adults 14 G) to maintain oxygenation. It is essential to confirm the position of the cannula in the trachea by aspirating air through the cannula before use. The upper airway must be patent to allow exhalation, otherwise overinflation and barotrauma may follow. Apnoeic oxygenation – in conjunction with TIVA, apnoeic oxy-genation of a paralysed patient is useful for fibre-optic endoscopy of routine cases in order to maintain endoscopic skills.

Airway patency: under general anaesthesia, loss of muscle tone leads to airway obstruction, rendering endoscopy impossible. Therefore, to permit endoscopy, airway patency must be main-tained by the manoeuvres outlined earlier. When mouth open-ing is very limited it may be impossible to open the posterior oropharyngeal space after induction of anaesthesia; under these circumstances the safe option is to secure the airway first under local anaesthesia.

Airway adjuncts: many masks and airways have been designed to facilitate airway maintenance and endoscopy. The LMA deserves special mention because it may be inserted in patients with limited mouth opening. When inflated, the cuff distends the laryngopharynx and creates a cavity around the laryngeal inlet into which an endoscope can be passed. The size 3 LMA (Figure 5) permits the passage of a 6.0 tracheal tube; both may be left in place during surgery. Alternatively, a larger tracheal tube is railroaded over an Aintree catheter (Figure 5), which is first placed by the fibrescope.

5 A size 3 laryngeal mask

permits the passage of a 6.5

tracheal tube as seen here

alongside an Aintree catheter.

fibre-optic intubation, including local anaesthesia for awake intubation

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