EUROANESTHESIA 2007 Munich, Germany, 9-12 June 2007

Transcription

1 LARYNGOSCOPY: PAST, PRESENT AND FUTURE EUROANESTHESIA 2007 Munich, Germany, 9-12 June 2007 EAMSRC1 JOHN HENDERSON Anaesthetic Department Gartnavel General Hospital Glasgow, UK Saturday Jun 9, :00-15:45 Room 14a The presence in the trachea of a cuffed tube provides the most reliable airway possible for major surgery and care of the critically ill patient. Direct laryngoscopy has been the standard technique used to facilitate tracheal intubation for more than 85 years. However the limitations of direct laryngoscopy are now recognised and new techniques for tracheal intubation under vision have been developed. THE PROBLEM WITH DIRECT LARYNGOSCOPY FOR TRACHEAL INTUBATION HISTORY The mortality and severe morbidity associated with tracheal intubation are well documented. Respiratory system adverse events in the American Society of Anesthesiologists (ASA) Closed Claims study decreased from 36% in the 1970s to 14% of claims in the 1990s. However, the proportion of claims associated with tracheal intubation has more than doubled [1], and problems with tracheal intubation were responsible for 48% of anaesthetic deaths in UK closed claims [2]. Six percent of claims in the ASA database are for airway injury, including mediastinitis, after difficult intubation. Multiple attempts at intubation are associated with death or brain damage [3]. Blind techniques should be limited to a maximum number of four attempts and skills in additional techniques of tracheal intubation under indirect vision should be developed, as has been highlighted in recent editorials [4, 5]. Tracheal intubation as an airway in anaesthesia was first used by Macewen, who used his fingers to guide the tube into the trachea. Most found this digital technique difficult and it was not widely used. The first use of direct laryngoscopy to facilitate tracheal intubation under vision was by Elsberg. The standard straight laryngoscope technique of direct elevation of the epiglottis was used. Tracheal intubation under vision became a routine technique. Magill used the straight laryngoscope from the side of the mouth, a technique later called the paraglossal technique. In 1943 Macintosh described his curved laryngoscope and novel technique of indirect elevation of the epiglottis. Although there was no evidence of greater efficacy, it became the only laryngoscopy technique used by most anaesthetists. The first report of a series of failed intubations with the Macintosh laryngoscope was published in 1956, to be followed by many more reports. The limitations of the Macintosh laryngoscope slowly became apparent [6]. THEORETICAL BASIS OF DIRECT LARYNGOSCOPY The structures which obstruct the line of sight from above the maxillary teeth to the larynx are the tongue and the epiglottis. The direct laryngoscope is used to displace the tongue laterally (normally to the left), the hyoid bone anteriorly and the epiglottis is elevated. Considerable pressure on the tissues may be necessary [7]. The lifting force should be sufficient to achieve an optimum view of the larynx without causing tissue trauma. Laryngoscopes designed for tracheal intubation should facilitate passage of the tracheal tube (TT). INCIDENCE AND ANATOMICAL BASIS OF FAILED LARYNGOSCOPY A low incidence of Cormack-Lehane grades 3 or 4 (e.g. 1.6% with external laryngeal pressure) with the Macintosh laryngoscope is often quoted, but figures of 10%, 11% and 13% have also been recorded. Factors which impair laryngoscope insertion, lateral displacement of the tongue or elevation of the epiglottis will impair the efficacy of direct laryngoscopy. Underlying anatomical factors include limited mouth opening, awkward dentition, hypoplastic mandible, temporo-mandibular joint dysfunction and limited head extension. The final common pathway of difficulty with the Macintosh laryngoscope is probably failure to completely displace the tongue so that some is trapped between the laryngoscope tip and the hyoid bone. The laryngoscope tip then cannot enter the vallecula and actually displaces the epiglottis into the line of sight

2 TRADITIONAL MANAGEMENT OF FAILED MACINTOSH LARYNGOSCOPY Blind techniques (with an introducer ( bougie ) or styletted TT) of finding the larynx and passing the TT are normally attempted when the larynx cannot be seen with the Macintosh laryngoscope. However there is a risk of failure, particularly when the epiglottis cannot be elevated from the posterior pharyngeal wall, and of airway trauma when force or repeated attempts are used [8]. Continued use of blind techniques should be questioned now that there are effective visual alternatives. ANTICIPATED AND UNANTICIPATED DIFFICULT INTUBATION Difficulty with laryngoscopy may be anticipated as a consequence of anatomical or pathological factors, or a history of previous difficult laryngoscopy [9]. Prevention of airway problems is always preferable to dealing with a critical situation in the unconscious, apnoeic patient. The safest plan for such patients is to perform tracheal intubation under topical anaesthesia while the patient is awake [4,10]. Awake intubation is only feasible with devices which cause minimal tissue distortion and hence discomfort. The most versatile instrument for use with this technique is the flexible fibreoptic laryngoscope (FFL). Awake intubation has many advantages. Ventilation, oxygenation and airway protection are preserved, provided that undue sedation is avoided. Normal pharyngeal tone and good tissue separation are preserved. Phonation, which can help identify the larynx, is possible. If this method is not successful, then other options such as postponement of surgery, elective surgical airway, or a trial of inhalational induction of anaesthesia are preserved. Awake fibreoptic intubation is unlikely to work in the presence of massive airway bleeding. It may be necessary to proceed to general anaesthesia in the few patients who will not tolerate awake intubation. Neuromuscular blockade should not be used in these patients until it is certain that effective ventilation can be achieved with a face mask or supraglottic device. The alternative rigid devices described later may be particularly useful in this situation. Unanticipated difficulty with direct laryngoscopy cannot be prevented as we do not know and cannot assess all contributing factors. Infrequent but important causes of unanticipated difficulty are laryngeal conditions such as lingual tonsil hypertrophy (LTH) [11]. Techniques which elevate the epiglottis directly can succeed in LTH, but considerable expertise is required. STRAIGHT LARYNGOSCOPE In 1983 Bonfils reported a series of patients in whom tracheal intubation under vision was achieved with the straight laryngoscope in patients in whom this had proved impossible with the Macintosh laryngoscope. This has subsequently been confirmed in several series, when the optimum technique is used [6]. The mechanism is probably both improved control of the tongue and more reliable elevation of the epiglottis. The straight laryngoscope is particularly indicated in laryngeal lesions including LTH, hypoplastic mandible and awkward dentition. Tissue distortion is necessary to create a line of sight, but the lifting forces are less than with the Macintosh laryngoscope [7]. Mastery of the straight laryngoscope is desirable, but development and maintenance of this skill requires considerable commitment. THEORETICAL BASIS OF INDIRECT LARYNGOSCOPY Direct laryngoscopy cannot always provide a view of the larynx. Features of the ideal indirect laryngoscopy device are shown in Table 1. No device meets all these criteria. TABLE 1. FEATURES OF IDEAL TECHNIQUE OF INDIRECT LARYNGOSCOPY Facilitates rapid tracheal intubation under vision Used with patient in neutral position Minimal tissue distortion required Few steps in technique TT passage integrated in design and technique High success rate in all clinical situations Competence is gained rapidly Equipment is simple, robust and inexpensive Preparation time is minimal Sterilisation is possible (or device is single-use)

3 The theoretical basis of indirect laryngoscopy is that the proximal end of the line of sight of the larynx is transferred from above the maxillary teeth to a position posterior to the base of the tongue. A view of the larynx is achieved from a position which cannot be achieved with direct laryngoscopy. Separation of anatomical structures to allow sight beyond the distal lens is essential. This separation may be achieved by external distraction of tissues (rarely necessary in the awake patient), displacement by the device itself (rigid indirect laryngoscopes (RILs)) or simultaneous use (frequently needed with optical stylets (OSs)) of a direct laryngoscope. These devices can be used with the patient s head and neck in a neutral position. They can be used with topical anaesthesia in the awake patient because minimal tissue displacement is needed. FLEXIBLE FIBREOPTIC LARYNGOSCOPE (FFL) Use of a flexible fibreoptic device to facilitate tracheal intubation was first described in 1967 and the use of a flexible fibreoptic bronchoscope to achieve awake intubation of a patient in whom intubation had previously failed was reported in It has long been accepted as the gold standard technique for management of anticipated difficult intubation [4,10]. Other indications are shown in Table 2. A low threshold for use of awake flexible fibreoptic intubation is particularly important in emergency patients in whom it might not be feasible to postpone surgery. TABLE 2. INDICATIONS FOR USE OF FLEXIBLE FIBREOPTIC LARYNGOSCOPE. Anticipated difficult tracheal intubation Anticipated difficult mask ventilation Anticipated difficult rescue technique Cervical spine instability Mediastinal mass Airway trauma TT change Control of flexion and extension of the tip of the FFL make it possible to steer it under vision around tissues as it is moved towards the larynx and trachea. It can facilitate tracheal intubation under vision in patients in whom no other technique could succeed. A very high success rate can be achieved [4]. Initially the route used was always nasal, but the oral route is now often seen as preferable. Whenever significant difficulty is anticipated, and particularly in the presence of stridor or reduced conscious level, sedation should not be used [12]. Considerable expertise is needed in such patients. The FFL is not the ideal device for every situation. The flexibility which contributes to its versatility in the elective patient can be disadvantageous in the emergency situation because rapid control of the position of the tip is not possible. ALTERNATIVE RIGID DEVICES DESIGNED TO FACILITATE TRACHEAL INTUBATION UNDER VISION Alternative rigid devices include rigid indirect laryngoscopes (RIL), optical stylets (OS) and miscellaneous devices. These rigid devices are not as versatile as the FFL but have the advantage in the unanticipated situation that their rigidity facilitates rapid control of the position of the laryngoscope tip. RIGID INDIRECT LARYNGOSCOPES (RILS) (INCLUDING VIDEO LARYNGOSCOPES ) Many RILs have been described in the last 2 decades. There is considerable variation in features, some of which are shown in Table 3. TABLE 3. DESIGN FEATURES OF RIGID INDIRECT LARYNGOSCOPES Design & technique of use Elevation of epiglottis technique Cost Portability work outside OR TT passage technique integrated or not Cleaning & sterilisation Quality of optics (ocular or video system) Anti-fog system Field of view Intensity & type of light

4 The rigidity of these devices allows retraction of soft tissues so that there is a line of sight from the lens to distal structures. The retraction force required is much less than in direct laryngoscopy so that these devices can be used under topical anaesthesia in the awake patient. The image may be transmitted proximally from the lens by fibreoptic bundles or prisms and lenses, or a distal camera may transmit the image to a video display. The most basic proximal optical system is an eyepiece. This can be used in a direct ocular technique or a camera can be attached. Integral or external video displays can be used. The term video laryngoscope is not a good descriptive term for these devices, as the display is not the key element in their success. Video display has advantages in both RILs and OSs. It facilitates the help of assistants, teaching and may improve success rates. The user does not require to follow the scope with his head. Modern devices provide much better illumination than traditional laryngoscopes. However, simple portable robust devices have the advantage that they can be ready for immediate use in an emergency. Several techniques of RIL use are recommended. All are used in the midline. Some displace the tongue to the left of midline, as in the Macintosh technique. Many RILs are passed over the dorsum of the tongue. Some of the latter group are used to elevate the epiglottis directly. Direct elevation of the epiglottis may succeed in patients in whom indirect elevation of the epiglottis is impossible, as in patients with LTH or other laryngeal lesions [13]. The TT is usually passed lateral or postero-lateral to the RIL and passage between the vocal cords is observed. Passage of TT can be difficult with those RILs in which TT passage is not integrated into the design [14]. Difficulty may increase the number and duration of attempts at TT passage and hence the risk of trauma and failure. In such RILs, the use of a stylet to deliver the TT to the glottis is recommended. The first RIL, the Bullard laryngoscope (Gyrus-ACMI, Southborough, MA, USA), was introduced in the late 1980s. A fibreoptic channel transmits the image from the distal lens to an eyepiece and a fibrelight channel transmits light to the distal end. It has a low profile, which facilitates use when mouth opening is limited. It is rotated through the oropharynx so that the tip comes to lie behind the epiglottis, which is elevated directly. Preformed stylets attached to the laryngoscope facilitate passage of the TT. Modifications of the original technique have improved the speed and reliability of TT passage. The technique of laryngoscopy and TT passage is not intuitive and some commitment is required to master the technique. The Bullard laryngoscope is simple, robust, requires minimal preparation time and has an unequalled evidence base. It has been used successfully in adult and paediatric difficult intubation, laryngeal disease, morbid obesity, maxillofacial injuries, limited mouth opening, ankylosing spondylitis and LTH. It may be the technique of choice in management of cervical spine injury as it provides a better view than the Macintosh laryngoscope, neck movement is minimal, and it can be used in awake patients under topical anaesthesia [15]. The Upsherscope (Mercury Medical, Clearwater Fl, USA)) and WuScope (Achi Corporation, San Jose CA, USA) are similar in concept to the Bullard. New RILs designed to elevate the epiglottis directly include the Pentax Airway Scope (Pentax Corporation, Japan). The Airtraq (Prodol Meditech SA, Spain) is an inexpensive single-use device. Other recent RILs include the Glidescope (Verathon, WA, USA) and McGrath (Aircraft Medical Ltd, Edinburgh UK), which use external and integrated video displays, respectively, of the image from a distal camera. The epiglottis may be elevated indirectly after the laryngoscope tip is positioned in the vallecula. Some users position the tip over the dorsum of the tongue, proximal to the epiglottis, achieving indirect elevation of the epiglottis without conventional tensioning of the hyoepiglottic ligament. Neither the Glidescope nor the McGrath has an integrated technique of TT passage. The view is usually better than that achieved with the Macintosh laryngoscope. Tracheal intubation can fail when the larynx is seen. Multiple attempts at TT passage may be required but the number and duration of attempts are not always reported [16]. Successful intubation under vision of patients in whom the use of the Macintosh laryngoscope failed has been reported. It is not clear whether these devices will work in the range of conditions in which the Bullard has been used successfully. OPTICAL STYLETS (OSS) Optical stylets incorporate a distal lens and optical system designed to facilitate their advancement into the larynx under vision [17]. They are robust and portable. The stylet with mounted TT is advanced under vision into the larynx. The TT is then advanced into the trachea. Midline or lateral techniques may be used [18]. OSs do not retract tissues and problems with misting, blood in the airway and failure to find anatomical structures have been reported. Although the pharynx may be opened with the jaw-thrust manoeuvre, displacement of the tongue and opening of the pharyngeal tissues with a Macintosh laryngoscope is used more frequently. This 2 device technique may require more co-ordination and time than use of a RIL. Although some claim that the technique is mastered rapidly, others state that it is not intuitive or express more serious reservations. Optical stylets may be rigid (e.g. Bonfils (Karl Storz, Tuttlingen, Germany)), malleable (e.g. Shikani or Levitan (both Clarus Medical, Minneapolis, MN, USA)) or have a tip which can be flexed and extended (e.g. SensaScope (Acutronic Medical Systems Ag, Switzerland)). There are reports of successful use of OSs in unanticipated difficult intubation [19]. They have been used successfully for passage of double-lumen tubes and in patients in whom use of the FFL proved difficult

5 OTHER DEVICES The ILMA is a very useful device for tracheal intubation in that it facilitates ventilation between intubation attempts, but it is not always successful. The ILMA success rate is improved when TT passage is guided by a FFL. The C-Trach (Intavent Orthofix Ltd, UK) is a variation of the ILMA design which includes fibreoptic image and fibrelight bundles. A unit which contains a camera and video display is attached after the C-Trach has been passed into the pharynx. The display facilitates optimum positioning of the device under vision, but the view remains poor in some patients [20]. The image is not as good as that produced by a conventional FFL, the principal problems being excessive secretions, inadequate light intensity and obstruction of the view by the epiglottis [20]. However the C-Trach has the advantage of being a relatively portable inexpensive system which can be prepared rapidly and facilitates ventilation between attempts at TT passage. There are now many reports of successful tracheal intubation under vision with the C-Trach in patients in whom intubation attempts with the FFL or ILMA had failed. CONCLUSIONS Exclusive use of the Macintosh laryngoscope with blind techniques for tracheal intubation exposes patients to the risk of avoidable morbidity and mortality. New techniques of tracheal intubation under vision have been developed. The FFL is the most versatile device and is normally the technique of choice for awake tracheal intubation of patients in whom difficult direct laryngoscopy is anticipated. FFL use can be difficult in an unanticipated difficult intubation. RILs, OSs and the C-Trach can facilitate rapid tracheal intubation under vision in such patients. We now have the means to move on from the combination of blind techniques with the Macintosh laryngoscope and should do so. We do not have the right to traumatise the airway and should aim to intubate all patients under vision. One or more of the devices described above should be available wherever anaesthesia is administered and all anaesthetists should develop and maintain skills in one or more of the techniques. Notice. Whilst every effort has been made to include most important devices, it is possible that some have been omitted inadvertently. Omission of any such device does not imply that it might not be useful in clinical management. CONFLICT OF INTEREST The author receives royalties from sales of the Henderson straight laryngoscope

6 REFERENCES 1. Lee LA, Domino KB. The Closed Claims Project. Has it influenced anaesthetic practice and outcome? Anesth Clin N Amer 2002; 20: Gannon K. Mortality associated with anaesthesia. A case review study. Anaesthesia 1991; 46: Peterson GN, Domino KB, Caplan RA, Posner KL, Lee LA, Cheney FW. Management of the difficult airway: a closed claims analysis. Anesthesiology 2005; 103: Popat M. State of the art: The airway. Anaesthesia 2003; 58: Crosby E. The unanticipated difficult airway evolving strategies for successful salvage. Can J Anaesth 2005; 52: Henderson JJ. Questions about the Macintosh laryngoscope and technique of laryngoscopy. Eur J Anaesthesiol 2000; 17: Hastings RH, Hon ED, Nghiem C, Wahrenbrock EA. Force and torque vary between laryngoscopists and laryngoscope blades. Anesth Analg 1996; 82: Cook TM. A new practical classification of laryngeal view. Anaesthesia 2000; 55: El-Ganzouri AR, McCarthy RJ, Tuman KJ, Tanck EN, Ivankovich AD. Preoperative airway assessment: predictive value of a multivariate risk index. Anesth Analg 1996; 82: Benumof JL. Management of the difficult adult airway. With special emphasis on awake tracheal intubation. Anesthesiology 1991; 75: Ovassapian A, Glassenberg R, Randel GI, Klock A, Mesnick PS, Klafta JM. The unexpected difficult airway and lingual tonsil hyperplasia: a case series and a review of the literature. Anesthesiology 2002; 97: Crosby ET. Complete airway obstruction. Canadian Journal of Anaesthesia 1999; 46: Crosby E, Skene D. More on lingual tonsillar hypertrophy. Can J Anaesth 2002; 49: Doyle DJ, Zura A, Ramachandran M. Videolaryngoscopy in the management of the difficult airway. Can J Anaesth 2004; 51: Hastings RH, Vigil AC, Hanna R, Yang BY, Sartoris DJ. Cervical spine movement during laryngoscopy with the Bullard, Macintosh, and Miller laryngoscopes. Anesthesiology 1995; 82: Sun DA, Warriner CB, Parsons DG, Klein R, Umedaly HS, Moult M. The GlideScope Video Laryngoscope: randomized clinical trial in 200 patients. Br J Anaesth 2005; 94: Liem EB, Bjoraker DG, Gravenstein D. New options for airway management: intubating fibreoptic stylets. Br J Anaesth 2003; 91: Halligan M, Charters P. A clinical evaluation of the Bonfils Intubation Fibrescope. Anaesthesia 2003; 58: Bein B, Yan M, Tonner PH, Scholz J, Steinfath M, Dorges V. Tracheal intubation using the Bonfils intubation fibrescope after failed direct laryngoscopy. Anaesthesia 2004; 59: Timmermann A, Russo S, Graf BM. Evaluation of the CTrachTM--an intubating LMA with integrated fibreoptic system. Br J Anaesth 2006; 96: