- Email: [email protected]
Alternative techniques for tracheal intubation
ENT/HEAD & NECK
Alternative techniques for tracheal intubation
Learning objectives After reading this article, you should be able to: C describe the alternative methods available for tracheal intubation C understand the functional limitations of the Macintosh blade C describe how the newer indirect optical devices attempt to address these limitations C understand why improved views do not necessarily mean easier intubation C appreciate why tissue trauma occurs and what can be done to minimize the risks
Seema Charters Peter Charters
Abstract Alternative rigid blade intubation devices available in recent years include the Glidescope, Airtraq and Bonfils laryngoscopes. The Macintosh blade works by displacing the tongue to one side and into the submandibular space while the tip of the device sits in the vallecula lifting the hyoid and so the epiglottis forward to reveal the laryngeal inlet. Under less favourable intubating conditions, the tongue is not accommodated in the submandibular space and tends to be compressed downwards. As a result the vallecula is not accessible and the blade tip is less able to be drawn forward. The retro-molar Bonfils avoids this problem by starting from a posterior position in the mouth and approaching the larynx below and alongside the tongue. The Bonfils also serves as a rigid stylet inside the tracheal tube again producing minimal tongue displacement. Airtraq also compresses the tongue less and usually sits on the posterior pharyngeal wall where it maintains the laryngeal view with a minimum of effort. It houses the tracheal tube in a channel that delivers it into the device’s field of view. While better optical systems have tended to improve visualization of the laryngeal inlet, this has not necessarily resulted in easier intubation conditions, shorter intubation times or improved overall success rates. Part of the problem has been that they have limited fields of view compared with the stereoscopic view of tube advancement down to the larynx as afforded by Macintosh.
clinical conditions (e.g. a ‘stiff neck’ due to degenerative arthritis) this may not be possible. An early solution for this was the introduction of optical prisms to ‘see round the corner’. Newer systems have continued with this aim and incorporated changes to the traditional blade shapes. The latter changes have generally been without specific evidence of any clear advantage and because clinical studies tend to only measure the view at laryngoscopy, it is not generally possible to determine the extent to which blade shape or optical changes individually contribute to any apparent advantage. Whether an individual patient proves to be difficult to intubate or otherwise is always a balance of factors. If the patient with a ‘stiff neck’ happens to be edentulous, the result is likely to be no difficulty. Equally some intubation devices are better at addressing certain challenges than others (e.g. flexible fibreoptic intubation via the nose in a patient with absolute trismus). Anticipated difficult intubation ‘scenarios’ are characterized by their associated ‘clinical problems’ and the ADAM (Aintree Difficult Airway Management) website1 exists to remind anaesthetists of all the relevant clinical problems for each scenario. This article will compare the alternative intubation devices, describing how they are used and how they help improve visualization of the airway, their limitations and complications, and how these may be overcome (Table 1 and Figure 1).
Keywords Airtraq; Bonfils; Glidescope; laryngoscopy; Macintosh laryngoscope; retro-molar laryngoscopy; tongue compression; tracheal intubation Royal College of Anaesthetists CPD matrix: 1CO2, 2AO1, 2AO3
Flexible fibreoptic intubation remains the gold standard for difficult intubation and the most adaptable approach currently available. However, in the last few years a number of alternative rigid blade devices have been introduced with various indirect optical viewing systems. In the normal erect, forwardlooking human, the maxillary line is approximately at right angles to the trachea and the traditional rigid blade approach has been to position the patient to try to straighten out this angle and allow a direct line of sight to the larynx. In certain
Depth of anaesthesia required As with traditional rigid devices, the newer indirect optical laryngoscopes require relaxed pharyngeal tone with moderate anaesthesia depth, but there is increasing experience of their use under sedation.2 By comparison, flexible fibrescopes are commonly used under sedation, local anaesthesia or both, and the patient is expected to be responsive enough to contribute to maintaining his/her own airway patency (i.e. conscious sedation). However, the NAP4 report urged caution when more complex sedation techniques are used and that a seditionist, not involved with the laryngoscopy, was needed.3 ‘Dedicated airways’ refer to the use of certain supraglottic airway devices (e.g. laryngeal mask airways (LMAs) or I-Gel) to maintain the airway while fibreoptic intubation is effected by means of delivering exchange catheters (e.g. Aintree Intubating Catheter). The exchange catheter is directed into the trachea and then used as a bougie over which the tracheal tube can then be advanced with minimal airway disturbance; general anaesthesia is usual.
Seema Charters FRCA is Consultant Anaesthetist at Warrington and Halton NHS Trust, Warrington, UK. Conflicts of interest: none. Peter Charters MRCP FRCA is Consultant Anaesthetist at University Hospital Aintree, Liverpool, UK. Elected Difficult Airway Society Professor for 2013. Conflicts of interest: Dr Charters is the inventor of the Aintree Intubation Catheter and has received royalties from the manufacturer, Cook International Ltd.
ANAESTHESIA AND INTENSIVE CARE MEDICINE 15:5
209
Ó 2014 Elsevier Ltd. All rights reserved.
ANAESTHESIA AND INTENSIVE CARE MEDICINE 15:5
Comparison of alternative techniques for tracheal intubation Functional class
Curved/straight blades
Visualization by Examples
Limiting physical tube advancement Main advantages in use Main limitations to success Complications
Channel devices
Modified LOS C-Mac Glidescope McGrath Numerous reports Valleculum/inlet only
Bougie commonly used to enter inlet ‘All round’ view Familiarity Poor mouth opening
Directed LOS Airtraq Pentax-AWS King Vision Numerous reports Above or below epiglottis/inlet only Limited space into which Increased tongue space tongue can be displaced* due to blade’s shape View up to tonsils then View up to tonsils then depends on device FOV depends on device FOV Blind spot from tonsils to Channel directed, emerges device FOV into device FOV Blind beyond inlet Blind beyond inlet Stylet use to match tube to Emerging tube not aligned curve of laryngoscope to inlet Optics improve view Optics improve view Similarity to Macintosh Less tongue compression Poor mouth opening Poor mouth opening
Dental trauma Laryngeal trauma
Blind spot injuries (Palatal and lateral wall)
Posterior pharyngeal wall injury
AIC, Aintree Intubation Catheter; FOV, field of vision; LMA, laryngeal mask airway; LOS, line of site Ó 2014 Elsevier Ltd. All rights reserved.
Table 1
Stylet articulated tip
Flexible fibrescope
‘Dedicated airway’
Intra-tubal visualization Bonfils (fixed) Shikani optical stylet Levitan (articulated) Numerous reports Below laryngeal inlet/high trachea Oral access may limit retro-molar positioning View up to tonsils then depends on device FOV Seen to mid trachea (Secretions/trauma can limit view) Rarely a problem (view point at tube tip) Optics improve view Tissues moved aside Manoeuvring device is not intuitive Uncommon (device is within tube)
Flexible probe Fibreoptic laryngoscope
Directed flexible probe LMA-AIC exchange
Common Low trachea/all trachea
Uncommon Low trachea/all trachea
Morphology constraints (e.g. blocked nostril) Limited to device FOV
Morphology constraints (e.g. pathological larynx) View up to tonsils then depends on device FOV Blind, final position good (Secretions/trauma can limit view) Essentially blind, many holdup possibilities No loss of airway Low-skill technique Sub-optimal position of LMA
Blind, final position good (Secretions/trauma can limit view) Essentially blind, many holdup possibilities Most flexible option Nasal or oral access Negotiating tight bends Tissues not moved aside Tube advance injuries
Tube advance injuries
ENT/HEAD & NECK
210
Direct LOS Macintosh Millar McCoy (levering tip) Use with sedation Uncommon Blade tip position/ Valleculum expected view (Macintosh)/inlet only Limiting blade tip Limited space into which positioning tongue can be displaced* Expected pathway ‘All round’ line of visualization site to inlet Limiting view of Blind beyond inlet tube advancement
Steering devices
ENT/HEAD & NECK
"Overlay" drawings of laryngoscopies for a single patient (a) Macint osh
(b) G lidescope
(c) Airt raq
(d) Bonfils
(e) Flexible fibrescope (nasal use)
(f) Dedicated airway (wit h flexible fibrescope, laryngeal mask airway and Aintree intubation catheter)
“Overlays” start with lateral photographs taken during maximal laryngeal exposure at laryngoscopy using a fixed camera distance from the subject's midline. Equivalent photographs of the devices are taken at the same fixed camera distance. The paired images are then imported into a digital software package and outlined using Bezière curves. The device images are then overlayed onto the photographic images with that part of the device which is showing (i.e. those parts outside the airway). The approximate position for the laryngeal Inlet is indicated by a line from the crico-thyroid membrane (marked in the patient prior to laryngoscopy). The angular width of the field of vision for each device is shown as two dotted lines indicating its extent. For Macintosh, an eye and dotted line are show to suggest maximum forward view possible.
Figure 1
Traditional curved/straight blades
allow time for complete muscle relaxation to occur but in ‘rapid sequence induction’, when cricoid pressure is used to protect against aspiration, further ventilation is not used before intubation. During intubation with a Macintosh blade an ‘all round view’ is usual and it is normally possible to see all of the tube in the airway on its way to the inlet. The usual problems with this technique are that the tongue is relatively large for the space into which it can be displaced. In the first place this is a minor inconvenience because even if only part of the larynx is seen it may still be possible to direct the tube into the larynx or a bougie over which a tracheal tube can be advanced. When the tongue displacement becomes more of an issue, identifying the vallecula becomes impossible and eventually no view of even the epiglottis
The traditional method of tracheal intubation in the UK has always been with Macintosh laryngoscopy. There is a small but regular failure rate with this device that can occur in patients who appear relatively normal to conventional bedside tests for difficulty. For this reason all anaesthetists should approach intubation by this method as something that will occasionally fail and the UK Difficult Airway Society have produced guidelines for management of the unanticipated difficult laryngoscopy.4 The technique starts with the patient being positioned in the ‘sniffing position’5 that involves flexion of the neck and extension of the head. Anaesthesia is induced and neuromuscular blocking agents are given. Normally mask ventilation is used to
ANAESTHESIA AND INTENSIVE CARE MEDICINE 15:5
211
Ó 2014 Elsevier Ltd. All rights reserved.
ENT/HEAD & NECK
Intra-tubal visualization (Bonfils)
tip is seen. Trying to intubate when no view of the inlet has been obtained risks trauma to the delicate laryngeal structures and other techniques should be considered for this eventuality.6
In the UK the most common device in this class is the Bonfils laryngoscope. It is a rigid stylet type of device with a curve tip and fibreoptic viewing system. Because of the rigid shape a large fibreoptic bundle is available and the view of the anatomical structures is ideal. As it sits within the tracheal tube and is intended for retro-molar use, the space required to use the instrument is the least of all the rigid laryngoscopes. It has been advocated for use in the management of laryngopharyngeal tumours because it can minimize trauma to friable tissue, while on the other hand it is rigid enough to displace tissue obstructing progress to the laryngeal inlet and down into the subglottis. It has a viewing port but is normally connected to a stack monitor. It can be used outside the operating theatre when a portable lightsource is needed. While reports of its use with local anaesthesia and/or sedation have occurred, in most cases it is used with general anaesthesia and full muscle paralysis. It is not a handed instrument so not only can it be used equally conveniently by a left-handed person but in the same way it is easy for most individuals to change the directing hand to suit the requirements of the airway anomaly. In use the instrument is quite unlike conventional laryngoscopes because of its length, and when used in difficult situations, fine control depends on allowing it to pivot on the teeth. Control of the tip when the handgrip is at the other end of the instrument is far from intuitive. The instrument is prepared so as to have the tracheal tube bevel just visible as a crescent shape on the imaging screen. Provided that the crescent remains visible the anaesthetist can be certain that the tube is not snagged up against any obstruction. The patient is placed in the sniffing position and after induction of anaesthesia, it is usual to displace the tongue to one side. The authors encourage use of the left hand to do this either by drawing it and the jaw forward together or by inserting a thumb into the corner of the mouth and pushing the tongue forward similar to conventional laryngoscopy.10 The right hand takes control of the instrument with a handgrip in the region where the light-source is connected. Initial insertion of the Bonfils is under direct vision and then the imaging screen is used to monitor and direct progress. The left hand eases the epiglottis forward and the instrument tip is passed under it and towards the inlet. The larynx is entered by directing the tip of the instrument in the direction of the middle of the left vocal cord and then moving rightwards under the opposite vocal cord into the subglottis. Once the tip is about a centimetre below the cords the left hand can be released and is then free to disengage the tracheal tube from its connector and so advance it on down the trachea. To remove the Bonfils from the tracheal tube it is important to do use a curving downwards and forwards direction over the front of the chest so that the tube is not removed from the trachea. Final confirmation of proper placement by capnography and bilateral auscultation is then completed.
Steering devices These are similar in shape to the Macintosh blade but have additional optical components that allow ‘seeing round the corner’. The expanded ‘field of vision’ (FOV) offered by the camera lens (situated proximal to the tip of the blade) improves the grade of laryngoscopy by modification of the line of sight. The lens view is transmitted to a video monitor and the anaesthetist directs the tracheal tube towards this view of the larynx, hence the name ‘steering devices’. Examples are C-Mac, Glidescope and McGrath laryngoscopes. The general recommendation is that these devices are inserted in the midline while the tip is positioned in vallecula, similarly to the Macintosh. The authors refer to these devices as ‘Mac-alike’ because they suffer from the same limitation as Macintosh (i.e. the need for tongue displacement and space to displace the tongue into). The other limitation is in respect of visualization because there is a tendency to have a blind spot behind the tongue and above the laryngeal inlet.7 The tracheal tube has to traverse this blind spot before it appears on the monitor screen. If the operator is not careful during its insertion, the tracheal tube can cause injury to pharyngeal structures in its path. This complication has been reported widely for Glidescope.8 The manufacturer recommends checking progress of the tube towards the blind area, rather than focussing solely on the monitor, to minimize the risk of injury. Another issue with use of these devices is difficulty with intubation despite an adequate laryngeal view. This is generally due to problems in steering the tube into the inlet. This is most easily overcome with a bougie or stylet inside the tube and curved to match the laryngoscope blade shape.
Channel devices The directed line of sight devices also have enhanced optical systems but incorporate a channel that houses the tracheal tube so that it emerges into the field of view of the instrument. This means that there is no blind spot equivalent to the steering devices. These devices are not considered to be ‘Macalike’ because the blade shapes cause very little tongue compression, accommodate the bulk of the tongue within their curvature and as a result are more likely to lie close to the posterior pharyngeal wall. In contrast to the steering devices, injuries to the posterior wall have occurred during insertion.9 Because the channel has to be big enough to enclose the tube, the bulk of the device can cause difficulty with insertion into the mouth. Examples of these devices are Airtraq and Pentax Airwayscope. As with steering devices, getting a view of the larynx is usually straightforward but intubation may not be. The tube exits from the channel at a fixed angle that will not always match the position of the device relative to the laryngeal inlet. The options are to move the blade tip closer to or further from the inlet or alternatively minor rotations of the tip may help. As the blade tends to lie on the posterior wall it is important to also consider trying to pull it upwards to change the angle of approach.
ANAESTHESIA AND INTENSIVE CARE MEDICINE 15:5
Flexible fibrescope The advantage of the flexible fibrescope is that it can be used for oral or nasal intubation and that deep sedation is not normally required so the patient continues breathing. Local anaesthesia and conscious sedation may help but explaining the procedure
212
Ó 2014 Elsevier Ltd. All rights reserved.
ENT/HEAD & NECK
This process generally starts with an unanticipated difficult intubation that has been rescued by use of a laryngeal mask or I-gel airway. In other words, ventilation and oxygenation are already stable but the anaesthetist still considers intubation the preferred option (e.g. when head and neck surgery is anticipated). A sealed-port angle-piece is used between the DA and the catheter mount to maintain ventilation. The AIC is loaded onto a fibrescope (maximum outer diameter 4.2 mm) that guides the AIC through the angle-piece down the channel of the DA to the laryngeal inlet and on to the carina. The AIC has centimetre marks to determine its position in the patient’s airway. Next, the fibrescope is removed leaving the AIC undisturbed. Up to this stage ventilation can proceed without interruption. The DA is then removed leaving only the AIC. This is critical because the length of the AIC is only as long as the fibrescope and there is a risk that removing the DA will displace the AIC from the trachea. To prevent this, the anaesthetist reaches into the back of the mouth to grasp the AIC as the DA is removed and during this and the next step no ventilation is normally required, although the AIC comes with Rapi-FitÔ adaptors that allow ventilation through the AIC if desired. The AIC is now the bougie over which a tracheal tube (internal diameter of 7 mm or larger) can be passed directly into the trachea. Again its position in the patient’s airway should be monitored by the centimetre marks, particularly when using longer tracheal tubes (e.g. uncut or preformed tubes) to avoid premature dislodgment of the AIC from the trachea. Finally the AIC is removed leaving just the tracheal tube and confirmation of its correct placement by capnography and bilateral auscultation can proceed.
and what may be expected to the patient at the various stages are generally more important. Vasoconstriction of the mucosa of the nose opens up the nasal passage and minimizes the risk of bleeding. The main drawbacks with this technique are the limited field of view with the instrument, which is important when either the airway is very abnormal and/or in the face of copious secretions or material contaminating the airway. The suction channel is not useful for thick or voluminous secretions. This technique is generally perceived as requiring moderate dexterity and familiarity with the device. Most commonly, the technique is used when difficult intubation is anticipated or the patient is not easily positioned for conventional intubation (e.g. severe trismus or limited head extension). The nasal approach requires no separate guide but oral intubation requires a Berman airway or equivalent. Some knowledge of the normal and common nasal pathologies (e.g. polyps and sinusitis) is helpful and attending ENT outpatient clinics to learn nasendoscopy from specialists is extremely useful. This also helps determine the most appropriate nostril for the instrumentation. After a nostril is chosen it is important to load a suitable nasotracheal tube onto the fibrescope before starting. After vasoconstriction and appropriate local anaesthesia and/or sedation has been achieved, the fibrescope is introduced along the floor of the nose and directed under the inferior turbinate. The first important structure beyond that is the mobile soft palate, the landmark for turning down into the pharynx. At this stage the epiglottis and larynx are usually visible in the distance and should be approached slowly, correcting the position of the fibrescope tip as the instrument is advanced. The patient is encouraged to protrude their tongue to expose the laryngeal inlet better. The patient is also encouraged to breathe regularly and deeply so that the anaesthetist can anticipate the moment for laryngeal entry as reflex coughing may occur. The tracheal tube is then advanced through the nose over the fibrescope. It is important to remember that this stage is blind, holdup is possible at the arytenoids or by airway pathologies and oesophageal intubation is possible. Even with adequate local anaesthesia this will tend to produce a withdrawal reaction unless it has been explained in advance. Once the tube is beyond the vocal cords the patient will have difficulty breathing past the tube and again this should have been explained beforehand. It is vital that the position of the tube is confirmed as quickly as possible (by noting its relationship to the carina and tracheal rings) allowing removal of the fibrescope and the breathing to become easier. It is usually possible to confirm proper tube placement by capnography before inducing anaesthesia. Only after induction can the cuff of the tracheal tube be inflated as to do so beforehand leads to airway obstruction prompting the patient into immediate self-extubation.
Conclusion The fibrescope has had a place in tracheal intubation since 1967 and the role of the new rigid alternatives to the Macintosh blade is becoming clearer with greater clinical experience. The new devices fulfil two essential roles; they address the main limitations of the Macintosh blade and minimize the number of ‘blind’ intubations (i.e. when there is no clear view of the tracheal tube entering the larynx). The earlier convention of a bougie passed blindly into the larynx risks injury because it is a blind procedure. The new risk of injury in the ‘blind spot’ region with steering devices is potentially a problem because the injury tends not to be recognized until the postoperative period. The recurring challenge for any further devices is the need to maximize the view of the anatomy, safe tube passage into the field of view and the final negotiation of laryngeal entry. It seems likely that optical technologies used will converge to a distal digital microcamera system with the option to wirelessly transmit the image to a screen. A
Dedicated airway/Aintree Intubation Catheter This technique combines the use of a laryngeal mask or I-gel airway, an Aintree Intubation Catheter (AIC) and a fibreoptic laryngoscope. The term ‘dedicated airway’ (DA) describes the relative guarantee of a secure airway (by the laryngeal mask or Igel) during the intubation process. In other words after the airway is secured in the first place, it should be expected to remain patent during the intubation process. It is generally considered to be a low-skill because the fibrescope is directed via the channel of the DA toward the laryngeal inlet.
ANAESTHESIA AND INTENSIVE CARE MEDICINE 15:5
REFERENCES 1 http://adam.liv.ac.uk. 2 Dimitriou V, Zogogiannis I, Liotiri D. Awake tracheal intubation using the Airtraq laryngoscope: a case series. Acta Anaesthesiol Scand 2009; 53: 964e7. 3 Popat M, Woodall N. Chpt 14 fibreoptic intubation: uses and omissions. www.rcoa.ac.uk/system/files/CSQ-NAP4-Full.pdf. Page 120. 4 http://www.das.uk.com/files/ddl-Jul04-A4.pdf.
213
Ó 2014 Elsevier Ltd. All rights reserved.
ENT/HEAD & NECK
8 Leong W, Lim Y, Sia A. Palatopharyngeal wall perforation during Glidescope intubation. Anaesth Intensive Care 2008; 36: 870e4. 9 Holst B, Hodzovic I, Francis V. Airway trauma caused by the Airtraq laryngoscope. Anaesthesia 2008; 63: 889e90. 10 Halligan M, Charters P. A clinical evaluation of the Bonfils intubation fibrescope. Anaesthesia 2003; 58: 1087e91.
5 Horton WA, Fahy L, Charters P. Disposition of the cervical vertebrae, atlanto-axial joint, hyoid and mandible during x-ray laryngoscopy. Br J Anaesth 1989; 63: 435e8. 6 Kardry M, Popat M. Pharyngeal wall perforation e an unusual complication of blind intubation with a gum-elastic bougie. Anaesthesia 1999; 54: 404e5. 7 Cooper RM. Complications associated with the use of the GlideScopeÒ videolaryngoscope. Can J Anesth 2007; 54: 54e7.
ANAESTHESIA AND INTENSIVE CARE MEDICINE 15:5
214
Ó 2014 Elsevier Ltd. All rights reserved.
Alternative techniques for tracheal intubation
Learning objectives After reading this article, you should be able to: C describe the alternative methods available for tracheal intubation C understand the functional limitations of the Macintosh blade C describe how the newer indirect optical devices attempt to address these limitations C understand why improved views do not necessarily mean easier intubation C appreciate why tissue trauma occurs and what can be done to minimize the risks
Seema Charters Peter Charters
Abstract Alternative rigid blade intubation devices available in recent years include the Glidescope, Airtraq and Bonfils laryngoscopes. The Macintosh blade works by displacing the tongue to one side and into the submandibular space while the tip of the device sits in the vallecula lifting the hyoid and so the epiglottis forward to reveal the laryngeal inlet. Under less favourable intubating conditions, the tongue is not accommodated in the submandibular space and tends to be compressed downwards. As a result the vallecula is not accessible and the blade tip is less able to be drawn forward. The retro-molar Bonfils avoids this problem by starting from a posterior position in the mouth and approaching the larynx below and alongside the tongue. The Bonfils also serves as a rigid stylet inside the tracheal tube again producing minimal tongue displacement. Airtraq also compresses the tongue less and usually sits on the posterior pharyngeal wall where it maintains the laryngeal view with a minimum of effort. It houses the tracheal tube in a channel that delivers it into the device’s field of view. While better optical systems have tended to improve visualization of the laryngeal inlet, this has not necessarily resulted in easier intubation conditions, shorter intubation times or improved overall success rates. Part of the problem has been that they have limited fields of view compared with the stereoscopic view of tube advancement down to the larynx as afforded by Macintosh.
clinical conditions (e.g. a ‘stiff neck’ due to degenerative arthritis) this may not be possible. An early solution for this was the introduction of optical prisms to ‘see round the corner’. Newer systems have continued with this aim and incorporated changes to the traditional blade shapes. The latter changes have generally been without specific evidence of any clear advantage and because clinical studies tend to only measure the view at laryngoscopy, it is not generally possible to determine the extent to which blade shape or optical changes individually contribute to any apparent advantage. Whether an individual patient proves to be difficult to intubate or otherwise is always a balance of factors. If the patient with a ‘stiff neck’ happens to be edentulous, the result is likely to be no difficulty. Equally some intubation devices are better at addressing certain challenges than others (e.g. flexible fibreoptic intubation via the nose in a patient with absolute trismus). Anticipated difficult intubation ‘scenarios’ are characterized by their associated ‘clinical problems’ and the ADAM (Aintree Difficult Airway Management) website1 exists to remind anaesthetists of all the relevant clinical problems for each scenario. This article will compare the alternative intubation devices, describing how they are used and how they help improve visualization of the airway, their limitations and complications, and how these may be overcome (Table 1 and Figure 1).
Keywords Airtraq; Bonfils; Glidescope; laryngoscopy; Macintosh laryngoscope; retro-molar laryngoscopy; tongue compression; tracheal intubation Royal College of Anaesthetists CPD matrix: 1CO2, 2AO1, 2AO3
Flexible fibreoptic intubation remains the gold standard for difficult intubation and the most adaptable approach currently available. However, in the last few years a number of alternative rigid blade devices have been introduced with various indirect optical viewing systems. In the normal erect, forwardlooking human, the maxillary line is approximately at right angles to the trachea and the traditional rigid blade approach has been to position the patient to try to straighten out this angle and allow a direct line of sight to the larynx. In certain
Depth of anaesthesia required As with traditional rigid devices, the newer indirect optical laryngoscopes require relaxed pharyngeal tone with moderate anaesthesia depth, but there is increasing experience of their use under sedation.2 By comparison, flexible fibrescopes are commonly used under sedation, local anaesthesia or both, and the patient is expected to be responsive enough to contribute to maintaining his/her own airway patency (i.e. conscious sedation). However, the NAP4 report urged caution when more complex sedation techniques are used and that a seditionist, not involved with the laryngoscopy, was needed.3 ‘Dedicated airways’ refer to the use of certain supraglottic airway devices (e.g. laryngeal mask airways (LMAs) or I-Gel) to maintain the airway while fibreoptic intubation is effected by means of delivering exchange catheters (e.g. Aintree Intubating Catheter). The exchange catheter is directed into the trachea and then used as a bougie over which the tracheal tube can then be advanced with minimal airway disturbance; general anaesthesia is usual.
Seema Charters FRCA is Consultant Anaesthetist at Warrington and Halton NHS Trust, Warrington, UK. Conflicts of interest: none. Peter Charters MRCP FRCA is Consultant Anaesthetist at University Hospital Aintree, Liverpool, UK. Elected Difficult Airway Society Professor for 2013. Conflicts of interest: Dr Charters is the inventor of the Aintree Intubation Catheter and has received royalties from the manufacturer, Cook International Ltd.
ANAESTHESIA AND INTENSIVE CARE MEDICINE 15:5
209
Ó 2014 Elsevier Ltd. All rights reserved.
ANAESTHESIA AND INTENSIVE CARE MEDICINE 15:5
Comparison of alternative techniques for tracheal intubation Functional class
Curved/straight blades
Visualization by Examples
Limiting physical tube advancement Main advantages in use Main limitations to success Complications
Channel devices
Modified LOS C-Mac Glidescope McGrath Numerous reports Valleculum/inlet only
Bougie commonly used to enter inlet ‘All round’ view Familiarity Poor mouth opening
Directed LOS Airtraq Pentax-AWS King Vision Numerous reports Above or below epiglottis/inlet only Limited space into which Increased tongue space tongue can be displaced* due to blade’s shape View up to tonsils then View up to tonsils then depends on device FOV depends on device FOV Blind spot from tonsils to Channel directed, emerges device FOV into device FOV Blind beyond inlet Blind beyond inlet Stylet use to match tube to Emerging tube not aligned curve of laryngoscope to inlet Optics improve view Optics improve view Similarity to Macintosh Less tongue compression Poor mouth opening Poor mouth opening
Dental trauma Laryngeal trauma
Blind spot injuries (Palatal and lateral wall)
Posterior pharyngeal wall injury
AIC, Aintree Intubation Catheter; FOV, field of vision; LMA, laryngeal mask airway; LOS, line of site Ó 2014 Elsevier Ltd. All rights reserved.
Table 1
Stylet articulated tip
Flexible fibrescope
‘Dedicated airway’
Intra-tubal visualization Bonfils (fixed) Shikani optical stylet Levitan (articulated) Numerous reports Below laryngeal inlet/high trachea Oral access may limit retro-molar positioning View up to tonsils then depends on device FOV Seen to mid trachea (Secretions/trauma can limit view) Rarely a problem (view point at tube tip) Optics improve view Tissues moved aside Manoeuvring device is not intuitive Uncommon (device is within tube)
Flexible probe Fibreoptic laryngoscope
Directed flexible probe LMA-AIC exchange
Common Low trachea/all trachea
Uncommon Low trachea/all trachea
Morphology constraints (e.g. blocked nostril) Limited to device FOV
Morphology constraints (e.g. pathological larynx) View up to tonsils then depends on device FOV Blind, final position good (Secretions/trauma can limit view) Essentially blind, many holdup possibilities No loss of airway Low-skill technique Sub-optimal position of LMA
Blind, final position good (Secretions/trauma can limit view) Essentially blind, many holdup possibilities Most flexible option Nasal or oral access Negotiating tight bends Tissues not moved aside Tube advance injuries
Tube advance injuries
ENT/HEAD & NECK
210
Direct LOS Macintosh Millar McCoy (levering tip) Use with sedation Uncommon Blade tip position/ Valleculum expected view (Macintosh)/inlet only Limiting blade tip Limited space into which positioning tongue can be displaced* Expected pathway ‘All round’ line of visualization site to inlet Limiting view of Blind beyond inlet tube advancement
Steering devices
ENT/HEAD & NECK
"Overlay" drawings of laryngoscopies for a single patient (a) Macint osh
(b) G lidescope
(c) Airt raq
(d) Bonfils
(e) Flexible fibrescope (nasal use)
(f) Dedicated airway (wit h flexible fibrescope, laryngeal mask airway and Aintree intubation catheter)
“Overlays” start with lateral photographs taken during maximal laryngeal exposure at laryngoscopy using a fixed camera distance from the subject's midline. Equivalent photographs of the devices are taken at the same fixed camera distance. The paired images are then imported into a digital software package and outlined using Bezière curves. The device images are then overlayed onto the photographic images with that part of the device which is showing (i.e. those parts outside the airway). The approximate position for the laryngeal Inlet is indicated by a line from the crico-thyroid membrane (marked in the patient prior to laryngoscopy). The angular width of the field of vision for each device is shown as two dotted lines indicating its extent. For Macintosh, an eye and dotted line are show to suggest maximum forward view possible.
Figure 1
Traditional curved/straight blades
allow time for complete muscle relaxation to occur but in ‘rapid sequence induction’, when cricoid pressure is used to protect against aspiration, further ventilation is not used before intubation. During intubation with a Macintosh blade an ‘all round view’ is usual and it is normally possible to see all of the tube in the airway on its way to the inlet. The usual problems with this technique are that the tongue is relatively large for the space into which it can be displaced. In the first place this is a minor inconvenience because even if only part of the larynx is seen it may still be possible to direct the tube into the larynx or a bougie over which a tracheal tube can be advanced. When the tongue displacement becomes more of an issue, identifying the vallecula becomes impossible and eventually no view of even the epiglottis
The traditional method of tracheal intubation in the UK has always been with Macintosh laryngoscopy. There is a small but regular failure rate with this device that can occur in patients who appear relatively normal to conventional bedside tests for difficulty. For this reason all anaesthetists should approach intubation by this method as something that will occasionally fail and the UK Difficult Airway Society have produced guidelines for management of the unanticipated difficult laryngoscopy.4 The technique starts with the patient being positioned in the ‘sniffing position’5 that involves flexion of the neck and extension of the head. Anaesthesia is induced and neuromuscular blocking agents are given. Normally mask ventilation is used to
ANAESTHESIA AND INTENSIVE CARE MEDICINE 15:5
211
Ó 2014 Elsevier Ltd. All rights reserved.
ENT/HEAD & NECK
Intra-tubal visualization (Bonfils)
tip is seen. Trying to intubate when no view of the inlet has been obtained risks trauma to the delicate laryngeal structures and other techniques should be considered for this eventuality.6
In the UK the most common device in this class is the Bonfils laryngoscope. It is a rigid stylet type of device with a curve tip and fibreoptic viewing system. Because of the rigid shape a large fibreoptic bundle is available and the view of the anatomical structures is ideal. As it sits within the tracheal tube and is intended for retro-molar use, the space required to use the instrument is the least of all the rigid laryngoscopes. It has been advocated for use in the management of laryngopharyngeal tumours because it can minimize trauma to friable tissue, while on the other hand it is rigid enough to displace tissue obstructing progress to the laryngeal inlet and down into the subglottis. It has a viewing port but is normally connected to a stack monitor. It can be used outside the operating theatre when a portable lightsource is needed. While reports of its use with local anaesthesia and/or sedation have occurred, in most cases it is used with general anaesthesia and full muscle paralysis. It is not a handed instrument so not only can it be used equally conveniently by a left-handed person but in the same way it is easy for most individuals to change the directing hand to suit the requirements of the airway anomaly. In use the instrument is quite unlike conventional laryngoscopes because of its length, and when used in difficult situations, fine control depends on allowing it to pivot on the teeth. Control of the tip when the handgrip is at the other end of the instrument is far from intuitive. The instrument is prepared so as to have the tracheal tube bevel just visible as a crescent shape on the imaging screen. Provided that the crescent remains visible the anaesthetist can be certain that the tube is not snagged up against any obstruction. The patient is placed in the sniffing position and after induction of anaesthesia, it is usual to displace the tongue to one side. The authors encourage use of the left hand to do this either by drawing it and the jaw forward together or by inserting a thumb into the corner of the mouth and pushing the tongue forward similar to conventional laryngoscopy.10 The right hand takes control of the instrument with a handgrip in the region where the light-source is connected. Initial insertion of the Bonfils is under direct vision and then the imaging screen is used to monitor and direct progress. The left hand eases the epiglottis forward and the instrument tip is passed under it and towards the inlet. The larynx is entered by directing the tip of the instrument in the direction of the middle of the left vocal cord and then moving rightwards under the opposite vocal cord into the subglottis. Once the tip is about a centimetre below the cords the left hand can be released and is then free to disengage the tracheal tube from its connector and so advance it on down the trachea. To remove the Bonfils from the tracheal tube it is important to do use a curving downwards and forwards direction over the front of the chest so that the tube is not removed from the trachea. Final confirmation of proper placement by capnography and bilateral auscultation is then completed.
Steering devices These are similar in shape to the Macintosh blade but have additional optical components that allow ‘seeing round the corner’. The expanded ‘field of vision’ (FOV) offered by the camera lens (situated proximal to the tip of the blade) improves the grade of laryngoscopy by modification of the line of sight. The lens view is transmitted to a video monitor and the anaesthetist directs the tracheal tube towards this view of the larynx, hence the name ‘steering devices’. Examples are C-Mac, Glidescope and McGrath laryngoscopes. The general recommendation is that these devices are inserted in the midline while the tip is positioned in vallecula, similarly to the Macintosh. The authors refer to these devices as ‘Mac-alike’ because they suffer from the same limitation as Macintosh (i.e. the need for tongue displacement and space to displace the tongue into). The other limitation is in respect of visualization because there is a tendency to have a blind spot behind the tongue and above the laryngeal inlet.7 The tracheal tube has to traverse this blind spot before it appears on the monitor screen. If the operator is not careful during its insertion, the tracheal tube can cause injury to pharyngeal structures in its path. This complication has been reported widely for Glidescope.8 The manufacturer recommends checking progress of the tube towards the blind area, rather than focussing solely on the monitor, to minimize the risk of injury. Another issue with use of these devices is difficulty with intubation despite an adequate laryngeal view. This is generally due to problems in steering the tube into the inlet. This is most easily overcome with a bougie or stylet inside the tube and curved to match the laryngoscope blade shape.
Channel devices The directed line of sight devices also have enhanced optical systems but incorporate a channel that houses the tracheal tube so that it emerges into the field of view of the instrument. This means that there is no blind spot equivalent to the steering devices. These devices are not considered to be ‘Macalike’ because the blade shapes cause very little tongue compression, accommodate the bulk of the tongue within their curvature and as a result are more likely to lie close to the posterior pharyngeal wall. In contrast to the steering devices, injuries to the posterior wall have occurred during insertion.9 Because the channel has to be big enough to enclose the tube, the bulk of the device can cause difficulty with insertion into the mouth. Examples of these devices are Airtraq and Pentax Airwayscope. As with steering devices, getting a view of the larynx is usually straightforward but intubation may not be. The tube exits from the channel at a fixed angle that will not always match the position of the device relative to the laryngeal inlet. The options are to move the blade tip closer to or further from the inlet or alternatively minor rotations of the tip may help. As the blade tends to lie on the posterior wall it is important to also consider trying to pull it upwards to change the angle of approach.
ANAESTHESIA AND INTENSIVE CARE MEDICINE 15:5
Flexible fibrescope The advantage of the flexible fibrescope is that it can be used for oral or nasal intubation and that deep sedation is not normally required so the patient continues breathing. Local anaesthesia and conscious sedation may help but explaining the procedure
212
Ó 2014 Elsevier Ltd. All rights reserved.
ENT/HEAD & NECK
This process generally starts with an unanticipated difficult intubation that has been rescued by use of a laryngeal mask or I-gel airway. In other words, ventilation and oxygenation are already stable but the anaesthetist still considers intubation the preferred option (e.g. when head and neck surgery is anticipated). A sealed-port angle-piece is used between the DA and the catheter mount to maintain ventilation. The AIC is loaded onto a fibrescope (maximum outer diameter 4.2 mm) that guides the AIC through the angle-piece down the channel of the DA to the laryngeal inlet and on to the carina. The AIC has centimetre marks to determine its position in the patient’s airway. Next, the fibrescope is removed leaving the AIC undisturbed. Up to this stage ventilation can proceed without interruption. The DA is then removed leaving only the AIC. This is critical because the length of the AIC is only as long as the fibrescope and there is a risk that removing the DA will displace the AIC from the trachea. To prevent this, the anaesthetist reaches into the back of the mouth to grasp the AIC as the DA is removed and during this and the next step no ventilation is normally required, although the AIC comes with Rapi-FitÔ adaptors that allow ventilation through the AIC if desired. The AIC is now the bougie over which a tracheal tube (internal diameter of 7 mm or larger) can be passed directly into the trachea. Again its position in the patient’s airway should be monitored by the centimetre marks, particularly when using longer tracheal tubes (e.g. uncut or preformed tubes) to avoid premature dislodgment of the AIC from the trachea. Finally the AIC is removed leaving just the tracheal tube and confirmation of its correct placement by capnography and bilateral auscultation can proceed.
and what may be expected to the patient at the various stages are generally more important. Vasoconstriction of the mucosa of the nose opens up the nasal passage and minimizes the risk of bleeding. The main drawbacks with this technique are the limited field of view with the instrument, which is important when either the airway is very abnormal and/or in the face of copious secretions or material contaminating the airway. The suction channel is not useful for thick or voluminous secretions. This technique is generally perceived as requiring moderate dexterity and familiarity with the device. Most commonly, the technique is used when difficult intubation is anticipated or the patient is not easily positioned for conventional intubation (e.g. severe trismus or limited head extension). The nasal approach requires no separate guide but oral intubation requires a Berman airway or equivalent. Some knowledge of the normal and common nasal pathologies (e.g. polyps and sinusitis) is helpful and attending ENT outpatient clinics to learn nasendoscopy from specialists is extremely useful. This also helps determine the most appropriate nostril for the instrumentation. After a nostril is chosen it is important to load a suitable nasotracheal tube onto the fibrescope before starting. After vasoconstriction and appropriate local anaesthesia and/or sedation has been achieved, the fibrescope is introduced along the floor of the nose and directed under the inferior turbinate. The first important structure beyond that is the mobile soft palate, the landmark for turning down into the pharynx. At this stage the epiglottis and larynx are usually visible in the distance and should be approached slowly, correcting the position of the fibrescope tip as the instrument is advanced. The patient is encouraged to protrude their tongue to expose the laryngeal inlet better. The patient is also encouraged to breathe regularly and deeply so that the anaesthetist can anticipate the moment for laryngeal entry as reflex coughing may occur. The tracheal tube is then advanced through the nose over the fibrescope. It is important to remember that this stage is blind, holdup is possible at the arytenoids or by airway pathologies and oesophageal intubation is possible. Even with adequate local anaesthesia this will tend to produce a withdrawal reaction unless it has been explained in advance. Once the tube is beyond the vocal cords the patient will have difficulty breathing past the tube and again this should have been explained beforehand. It is vital that the position of the tube is confirmed as quickly as possible (by noting its relationship to the carina and tracheal rings) allowing removal of the fibrescope and the breathing to become easier. It is usually possible to confirm proper tube placement by capnography before inducing anaesthesia. Only after induction can the cuff of the tracheal tube be inflated as to do so beforehand leads to airway obstruction prompting the patient into immediate self-extubation.
Conclusion The fibrescope has had a place in tracheal intubation since 1967 and the role of the new rigid alternatives to the Macintosh blade is becoming clearer with greater clinical experience. The new devices fulfil two essential roles; they address the main limitations of the Macintosh blade and minimize the number of ‘blind’ intubations (i.e. when there is no clear view of the tracheal tube entering the larynx). The earlier convention of a bougie passed blindly into the larynx risks injury because it is a blind procedure. The new risk of injury in the ‘blind spot’ region with steering devices is potentially a problem because the injury tends not to be recognized until the postoperative period. The recurring challenge for any further devices is the need to maximize the view of the anatomy, safe tube passage into the field of view and the final negotiation of laryngeal entry. It seems likely that optical technologies used will converge to a distal digital microcamera system with the option to wirelessly transmit the image to a screen. A
Dedicated airway/Aintree Intubation Catheter This technique combines the use of a laryngeal mask or I-gel airway, an Aintree Intubation Catheter (AIC) and a fibreoptic laryngoscope. The term ‘dedicated airway’ (DA) describes the relative guarantee of a secure airway (by the laryngeal mask or Igel) during the intubation process. In other words after the airway is secured in the first place, it should be expected to remain patent during the intubation process. It is generally considered to be a low-skill because the fibrescope is directed via the channel of the DA toward the laryngeal inlet.
ANAESTHESIA AND INTENSIVE CARE MEDICINE 15:5
REFERENCES 1 http://adam.liv.ac.uk. 2 Dimitriou V, Zogogiannis I, Liotiri D. Awake tracheal intubation using the Airtraq laryngoscope: a case series. Acta Anaesthesiol Scand 2009; 53: 964e7. 3 Popat M, Woodall N. Chpt 14 fibreoptic intubation: uses and omissions. www.rcoa.ac.uk/system/files/CSQ-NAP4-Full.pdf. Page 120. 4 http://www.das.uk.com/files/ddl-Jul04-A4.pdf.
213
Ó 2014 Elsevier Ltd. All rights reserved.
ENT/HEAD & NECK
8 Leong W, Lim Y, Sia A. Palatopharyngeal wall perforation during Glidescope intubation. Anaesth Intensive Care 2008; 36: 870e4. 9 Holst B, Hodzovic I, Francis V. Airway trauma caused by the Airtraq laryngoscope. Anaesthesia 2008; 63: 889e90. 10 Halligan M, Charters P. A clinical evaluation of the Bonfils intubation fibrescope. Anaesthesia 2003; 58: 1087e91.
5 Horton WA, Fahy L, Charters P. Disposition of the cervical vertebrae, atlanto-axial joint, hyoid and mandible during x-ray laryngoscopy. Br J Anaesth 1989; 63: 435e8. 6 Kardry M, Popat M. Pharyngeal wall perforation e an unusual complication of blind intubation with a gum-elastic bougie. Anaesthesia 1999; 54: 404e5. 7 Cooper RM. Complications associated with the use of the GlideScopeÒ videolaryngoscope. Can J Anesth 2007; 54: 54e7.
ANAESTHESIA AND INTENSIVE CARE MEDICINE 15:5
214
Ó 2014 Elsevier Ltd. All rights reserved.