Department of Anaesthesiology, Kansai Medical University, 10-15 Fumizono-cho, Moriguchi City, Osaka 5708507, Japan
*Corresponding author. E-mail: asait{at}takii.kmu.ac.jp
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Abstract |
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Keywords: equipment, bronchoscopes fibreoptic; equipment, tubes tracheal
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Introduction |
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To solve the first difficulty, several manoeuvres (such as thrusting the jaw forward, extension of the head, or traction of the tongue) have been proposed, and airway intubators (such as the Berman,17 Ovassapian66 and Williams87) have been developed. In addition, there have been comprehensive articles discussing effective ways of teaching fibrescopy.58 66 69 85 In contrast, there have been no textbooks or reviews which comprehensively deal with the second difficulty, of advancing a tracheal tube over a fibrescope. Therefore, the main aim of this review article is to analyse the incidence of, causes of and possible solution to, the difficulty in advancing a tube over a fibrescope into the trachea.
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Problems associated with difficult intubation over a fibrescope |
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The second problem associated with difficult fibreoptic intubation is damage to the upper airway. Repeated attempts at inserting a fibrescope into the trachea and advancing a tube over the scope increase the risk of injury to the larynx and surrounding tissues, leading to bleeding from, or oedema of, the tissues. Although rare, complete airway obstruction could occur during attempts at fibreoptic intubation even when the patient is not anaesthetized.18 59 What tends to be ignored is that at no time during insertion of a tracheal tube over a fibrescope can the tip of the tube be seen directly. Therefore, a tracheal tube should be advanced over a fibrescope with great caution, particularly in patients with pathological changes to the glottis or surrounding tissues.44 In a patient with laryngeal papillomatosis, repeated attempts at passing a tube over a successfully inserted fibrescope into the trachea resulted in massive bleeding, necessitating an emergency surgical airway.83
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Incidence of difficult intubation over a fibrescope |
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Causes of difficult intubation over a fibrescope |
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There has at least been agreement that the right arytenoid cartilage is more likely than the left arytenoid cartilage to obstruct the passage of a tube.9 48 77 This can be explained by the direction of the bevel of a tracheal tube:31 when a precurved tube is advanced over a fibrescope, the bevel of the tube is usually facing the left and the tip of the tube is on the right, and thus the tip of the tube is likely to impinge on the right arytenoid cartilage, rather than the left (Fig. 2).
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Hughes and Smith43 have suggested that the incidence of impingement of a tracheal tube might be greater when the tube is inserted through the right nostril than the left. In their study, the tube was impinged in eight of 15 patients (53%) when it was passed through the right nostril and in three of 15 patients (20%) when it was passed through the left nostril. Nevertheless, there was no significant difference between groups. It is not known whether there was no clinically meaningful difference between groups or whether the absence of the significance was because of an insufficient number of patients studied (false negative).
Katsnelson and colleagues48 claimed, from a study using mannequins, that the epiglottis is the main site (except for the nasal passage) which obstructs the passage of a tube during nasal fibreoptic intubation. They speculated that the difference in sites of obstruction between oral intubation (the right arytenoid cartilage) and nasal intubation (the epiglottis) resulted from the difference in alignment of the oral, pharyngeal and laryngeal axes in oro- and nasotracheal intubation. Nakayama and colleagues63 assessed the site of obstruction in patients for nasal fibreoptic intubation. In contrast to Katsnelson and colleagues, they suggested that the arytenoid cartilage was the main site of obstruction.
Oesophageal intubation
A tracheal tube may be inadvertently inserted into the oesophagus even when a fibrescope has been correctly inserted into the trachea.38 42 50 60 The incidence of migration of a tube into the oesophageal inlet can be high: in one report, this occurred in four of 10 patients (40%),9 whereas in another study it occurred in eight of 13 patients (62%) when a tube was passed over a gum elastic bougie.33 On 510% of occasions, migration of the tube into the oesophagus is unnoticed until the fibrescope is removed from the trachea.38 50
A few possible reasons for deviation of the tip of the tube towards the oesophageal inlet have been suggested.50 The first possibility is that a small part of the tip of the tube impinges on the laryngeal inlet and the tube then slips off into the oesophagus. The second possibility is that, when the tube is pulled back after it has been obstructed by the laryngeal inlet, the fibrescope may be pulled out of the trachea.50 However, these are probably not the main causes. Asai and colleagues9 investigated the problem by using a second fibrescope to observe the passage of a tube, which was inserted nasally into the oral cavity: the tube never impinged on the arytenoid cartilage and slipped off into the oesophagus, but was always advanced directly into the oesophagus, ignoring the course of the fibrescope. In this study, it also became apparent that, in the case of inadvertent insertion of the tube into the oesophageal inlet, there may have been resistance while a tracheal tube was being advanced, because the tube was pushing the mid-segment of the fibrescope into the oesophagus, not because the tube was impinging on the arytenoid cartilage before slipping off into the oesophagus (Fig. 3A).9 The tracheal tube may be continually advanced into the oesophagus, pulling the fibrescope out of the trachea, over the interarytenoid notch and into the oesophagus (Fig. 3B).9 36 60
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Other anatomical factors
Deformity of the upper airway or distortion of the airway (by an intrinsic or extrinsic tumour) has been reported to obstruct the passage of a tube over a fibrescope.35 40 83
Size of fibrescopes and tracheal tubes
Several studies have shown that the sizes of the fibrescope and tracheal tube affect the ease of passage of a tube over a fibrescope. Basically, the greater the gap between a fibrescope and a tracheal tube, the higher the likelihood of difficulty in advancing a tube over a fibrescope (Fig. 1).50 57 The texture and shape of tracheal tubes can also alter the ease of intubation over a fibrescope. The details of these factors will be described in the next section, with possible solutions.
Murphy eye of a tube
If the tip of a fibrescope is inadvertently advanced though a side hole (Murphy eye) of a tracheal tube, it becomes impossible to advance the tube into the trachea (Fig. 4).65
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Cricoid pressure
In one report, cricoid pressure, which was applied during rapid-sequence induction of anaesthesia, obstructed passage of a tube over a fibrescope into the trachea in two of 30 patients.68
Jaw thrusting
Thrusting the jaw forward widens the oropharyngeal cavity and opens the laryngeal inlet, thus easing insertion of a fibrescope into the trachea.1 61 On occasions, this manoeuvre may make it more difficult to pass a tube over the fibrescope into the trachea, however.38 The reason for this is not clear, but one possibility is that thrusting the jaw forward shifts the larynx anteriorly and widens the oesophageal inlet so that the tube is more likely to be inserted into the inlet.
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Solutions |
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Reduction of the gap between a fibrescope and a tracheal tube
One method of reducing the difficulty in advancing a tracheal tube over a fibrescope is to minimize the gap between the fibrescope and the tracheal tube. There are a few methods of achieving this: (i) use of a thick fibrescope and a thin tracheal tube; (ii) use of a tapered tube; and (iii) use of a gap-filler.
Use of a thick fibrescope and a thin tracheal tube
In one report, the ease of oral fibreoptic intubation was compared between an 8.0 mm ID and a 6.0 mm ID flexible tracheal tube.50 When a 6.0 mm tracheal tube was used, it was easy to pass the tube over the fibrescope (diameter 4.0 mm) into the trachea in 11 patients (55%), whereas when an 8.0 mm tube was used it was only easy in two of 20 patients (10%).50 Another study showed that the incidence of difficulty was lower using a thicker (diameter 5 mm) fibrescope (11%) than using a thinner (3.7 mm) scope (35%).38 Therefore, the use of a fibrescope of large diameter and a tracheal tube of narrow diameter would reduce the incidence of difficulty in advancing the tube over the fibrescope.
Use of a tapered tracheal tube
The gap between a fibrescope and a tube can be reduced if the tip of the tube is tapered. Jones and colleagues46 developed such a tube (the Moore tube), and showed that tracheal intubation with the Moore tube was much easier than intubation with a conventional tube. This tube is not commercially available.
Use of a gap-filler
Another way of reducing the gap between a tracheal tube and a fibrescope is to thread another, thinner tube into the tracheal tube. By cutting a 7.0-mm or 8.0-mm ID tube to the oral length of 23 cm, and by threading it over a well lubricated, uncuffed and uncut thinner tube (e.g. 5.0 mm ID), the inner tube can protrude beyond the end of the outer tube (Fig. 5). When these two tubes are threaded over a fibrescope, the thinner tube fills the gap that otherwise exists between the outer tube and the fibrescope (Fig. 5). After successful insertion of the fibrescope and the two tubes into the trachea, the fibrescope and the inner tube are removed. In one report, in 30 patients in whom difficult laryngoscopy was predicted and there was resistance to advancement of a thick tracheal tube (7.0 or 8.0 mm ID) over an orally inserted fibrescope, advancing the thick tube over a thinner tube (5.0 mm ID) and over a fibrescope was smooth in all patients.57 The effectiveness of this technique has been confirmed by another study.73 Instead of using a thin tracheal tube, an especially tailored polyvinyl chloride sleeve can be used to fill the gap between a tracheal tube and a fibrescope.14 With this technique, the sleeve would not only fill the gap between the tube and the fibrescope, but also reduce the incidence of the fibrescope being looped over the tip of the tube.
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Use of the Parker Flex-TipTM tube
The Parker Flex-TipTM tracheal tube (Parker Medical, Englewood, CO, USA), which is a polyvinyl chloride tube and has a flexible tip positioned towards the centre of its distal lumen (Fig. 6), has been reported to be easier than the conventional polyvinyl chloride tube to pass over a fibrescope into the trachea (Fig. 1).15 51 In one report, tracheal intubation over a fibrescope was smooth in four of 38 patients (11%) when a conventional tube was used, whereas it was smooth in 27 of 38 patients (71%) when the Parker tube was used.51 Similarly, in another study with a cross-over design, fibreoptic intubation was successful at the first attempt in seven of 17 patients (41%) for the conventional tube and in 13 of 17 patients (76%) for the Parker tube.15 The ease of advancing a Parker tube over an airway exchange catheter has also been shown.55
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Use of a flexible tube
A flexible tube is easier than a polyvinyl chloride tube to pass over an orally inserted fibrescope into the trachea,24 25 41 because a flexible tube can change its direction more easily to follow the curve of a fibrescope (Fig. 1). In one study of 20 patients, when a polyvinyl chloride tube was used, fibreoptic intubation was successful at the first attempt in only seven of 20 patients (35%), whereas for a flexible tube it was successful in 19 of 20 patients (95%).24
For nasal fibreoptic intubation, a flexible tube may not be as useful. In one study, there was no difficulty in advancing a polyvinyl chloride tube in eight of 16 patients nasally and a flexible tube in nine out of 16 patients.16 The reason for this finding is not known.
Use of an ILM flexible tube
The intubating laryngeal mask airway tube is a tube originally designed to pass through the intubating laryngeal mask airway into the trachea. The bevel of this tube is made of silicone and is softer than the conventional polyvinyl chloride tube; the bevel is hemispherical, with the leading edge in the midline; and the tube is also more flexible than the conventional tube (Fig. 6). Several studies have shown that insertion of this tube over the fibrescope into the trachea (without the use of the intubating laryngeal mask airway) is almost always easy (90100%) (Fig. 1).16 37 54 There has also been a report of two patients in whom insertion of a polyvinyl chloride tube over a fibrescope failed, but fibreoptic intubation using the intubating laryngeal mask airway tube was easy.34
Warming of a tracheal tube
Several authors have suggested that fibreoptic intubation may become easier when a polyvinyl chloride tube is warmed (by hot water or hot air), because the tube becomes softer and thus more easily follows the curve of a fibrescope into the trachea.29 30 41 49 However, there has been no clear evidence to support or reject the usefulness of this idea. In one study, the ease of fibreoptic intubation was assessed for warmed and non-warmed polyvinyl chloride tubes.41 The non-warmed tube was easily inserted into the trachea in 10 of 30 patients (33%) and the warmed tubes in 18 of 30 patients (60%). This difference (27%) seems marked, but there was no significant difference between the two groups. It is possible that the number of patients studied was too small to detect a clinically meaningful difference (false negative). In another study, the ease of fibreoptic orotracheal intubation was assessed using flexible tubes and warmed polyvinyl chloride tubes.30 Intubation was easy in 13 of 25 patients (52%) using flexible tubes and 17 of 25 patients (68%) using warmed polyvinyl chloride tubes; there was no significant difference between groups. This result might mean that tracheal intubation with a warmed polyvinyl chloride tube is as easy as intubation with a flexible tube, but it is not clear whether insertion of the warmed polyvinyl chloride tube is easier than insertion of a non-warmed tube.
Loading a tube over a fibrescope
When a tracheal tube is inserted into the nose or mouth and then an attempt is made to pass a fibrescope through the tube into the trachea, the tip of the fibrescope can pass through the side hole of the tube (Murphy eye) and tracheal intubation fail. This complication can be easily avoided either by loading a tracheal tube over a fibrescope before attempting fibreoptic intubation, or by advancing a fibrescope under direct vision until the fibrescope has passed through the distal orifice of the tube. The latter method may be more suitable for nasal fibreoptic intubation, because with the former method it may not be possible to insert a tube loaded over a fibrescope through a narrowed nasal passage after successful insertion of the fibrescope into the trachea.27
Removal of an airway intubator
Once the fibrescope has been inserted into the trachea, it may be better to remove an airway intubator (such as the Ovassapian airway), as it might hamper passage of a tracheal tube.41 68 72
Rotation of a tube
When a bevelled tracheal tube is used, rotation reduces the difficulty in advancing a tube over a fibrescope,31 33 50 by reducing the incidence of impingement of the tube on the right arytenoid cartilage or the right vocal cord, of oesophageal intubation, or the tube sticking to the anterior surface of the subglottis.
Rotation of the tube at random might enable intubation, but 90° anticlockwise rotation should be most effective in reducing impingement on the tube.31 When a tracheal tube is advanced over a fibrescope, the bevel of the tube is facing the left and thus the tip of the tube is liable to impinge on the right arytenoid cartilage or the right vocal cord (Fig. 2). If the tube is rotated 90° clockwise (Fig. 7A), the tip of the tube lies posterior to the fibrescope and may become impinged behind the arytenoids. In contrast, 90° anticlockwise rotation of the tube brings it into close contact with the fibrescope, minimizing impingement (Fig. 7B).31 When the tube is rotated 180°, the tip of the tube is liable to impinge on the left arytenoid cartilage or the left vocal cord (Fig. 7C). Several studies have confirmed that 90° anticlockwise rotation of the tube decreases the likelihood of difficulty in advancing a tube over a fibrescope43 46 50 77 or gum elastic bougie.33
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Rotation of a tube may not be effective in some circumstances.16 38 50 This method may be less effective if a tracheal tube of a large diameter is used.38 50 In one study, in which two sizes (6.0 and 8.0 mm ID) of flexible tube were used, there was resistance to advancing a 6.0 mm tube in nine of 20 patients and a 8.0 mm tube in 18 patients. Rotation of the 6.0 mm tube allowed intubation in eight of the nine patients (89%), whereas rotation of the 8.0 mm tube allowed intubation in only six of the 18 patients (33%).50 Nor may rotation of the tube be effective for nasal fibreoptic intubation.16 This may result from the epiglottis being the main obstruction to smooth intubation in these circumstances, so that rotation of the tube would not solve the problem. Lastly, rotation in itself will not be effective if the tube has been inserted into the oesophageal inlet.9 Withdrawing the tube for a few centimetres will be necessary before rotating and advancing the tube into the trachea.50
Release of jaw thrust
It may be better to release the jaw thrust when a tube is passed over a fibrescope, because jaw thrusting may increase the likelihood of difficulty in advancing a tube.38
Flexion of the neck
Flexion of the neck may make it possible to intubate over a fibrescope when the tube cannot be advanced into the trachea despite rotation.38 The explanation for this successful manoeuvre is uncertain, but it might be that the tip of the tracheal tube is impinging on the anterior, inner surface of the subglottis and flexion of the neck relieves the problem.
Cricoid pressure
Another possible reason for difficulty in fibreoptic intubation is inadvertent oesophageal intubation. Thus, occlusion of the oesophageal inlet by application of pressure over the cricoid cartilage, in theory, increases the success rate of fibreoptic intubation. This has been confirmed by one study, in which patients were randomly allocated to receive either cricoid pressure (19 patients) or sham pressure (21 patients), and the success rate of oral fibreoptic intubation was assessed.9 When no pressure was applied to the cricoid cartilage, tracheal intubation was successful within 60 s in only seven of 21 patients (33%), whereas when cricoid pressure was applied, tracheal intubation was successful within 60 s in 12 of 19 patients (63%). In this study, polyvinyl chloride tubes were used, and thus it is not known how often cricoid pressure facilitates passage of a flexible tube over the fibrescope into the trachea. As cricoid pressure can also make it difficult to intubate,68 it should be released and other techniques used if it is still difficult to advance a tube into the trachea.
Use of a laryngoscope
Oropharyngeal tissues, such as the root of the tongue or the epiglottis, may obstruct the passage of a tracheal tube over the fibrescope. Insertion of a laryngoscope may reduce the difficulty in passing a tube over a fibrescope, by lifting these tissues in an anterior direction and by opening up the glottis. In a study of patients without difficult airways, insertion of a tracheal tube over a fibrescope was difficult in six out of 10 patients even with rotation of the tube; in all of these patients, insertion of a laryngoscope enabled fibreoptic intubation.50 Similar findings were found in another study, in which tracheal intubation over a gum elastic bougie was easier with the aid of a laryngoscope than without it.33 Insertion of the McCoy laryngoscope and levering the tip of the blade allowed fibreoptic intubation in one patient in whom tracheal intubation using a laryngoscope had failed, and in whom a downfolded epiglottis prevented insertion of a tube over the fibrescope.7 As laryngoscopy also facilitates location of the glottis with the fibrescope and insertion of the scope into the trachea,32 45 75 76 a laryngoscope can be inserted before attempting fibreoptic intubation.
Use of digital aid
Tracheal intubation was achieved using the fingers until the Macintosh and Miller laryngoscopes were introduced into clinical practice.78 84 As with laryngoscopy, insertion of the index finger into the vallecula to open up the glottis by shifting the epiglottis anteriorly may ease fibreoptic intubation. Successful use of this technique has been reported in a patient who required neck stabilization, in whom passage of a tube over the fibrescope into the trachea had failed even after several different manoeuvres, such as rotation of the tube.7
Viewing through, or movement of, a fibrescope
Inadvertent insertion of a tracheal tube into the oesophagus is one major cause of failure. Any method which can detect migration of the tube into the oesophageal inlet before inadvertent removal of a fibrescope from the trachea would be useful. In one method, the operator keeps looking through the fibrescope while advancing the tube over the scope until the tip of the tube comes into view.36 If the tracheal carina goes out of view, the tube is likely to have migrated into the oesophagus. Nevertheless, many anaesthetists ask assistants to hold the fibrescope, so that they can hold the tracheal tube and flexible cord of the fibrescope, and do not look through the fibrescope during attempts at advancing the tube. A live video display of the fibreoptic view would solve this problem. Another method is to monitor capnography when advancing a tube.10 If the end-tidal carbon dioxide concentration becomes zero, the tip of the tube may have gone into the oesophageal inlet. When oesophageal intubation is suspected, the tube is pulled back before rotating and advancing it.
Use of the laryngeal mask airway
Classic laryngeal mask airway
The laryngeal mask airway has been widely used during anaesthesia, and it can also be used to facilitate tracheal intubation.4 23 Brain chose to attach a tube to the back of the mask at an angle of about 30°, because he had found that this was the optimal angle for tracheal intubation through the laryngeal mask.20 He later developed the intubating laryngeal mask airway, especially for tracheal intubation through the device.21 22 Since the first description by Brain,19 there have been numerous reports of successful fibreoptic intubation through the laryngeal mask in patients who were known to be difficult to intubate3 79 or in whom tracheal intubation with both a laryngoscope and a fibreoptic bronchoscope had failed.4 53 By passing a fibrescope and a tube through the laryngeal mask airway, Silk and colleagues79 intubated the trachea within 2 min in 46 of 48 patients with predicted difficult airways.
Fibreoptic intubation through the laryngeal mask airway has two major advantages over conventional fibreoptic intubation. First, the laryngeal mask facilitates location of the glottis using a fibrescope, because the glottis is usually positioned just below the grille of the mask and thus the distance between the grille and the vocal cords is only a few centimetres.6 The second advantage is that the laryngeal mask reduces the incidence of difficulty in passing a tracheal tube over a fibrescope, because the laryngeal mask bypasses obstacles, such as a narrowed pharyngeal cavity or the epiglottis, and restricts lateral or posterior deviation of the tracheal tube from the glottis.2 50
In one report, the ease of fibreoptic intubation with and without the use of the laryngeal mask was compared.50 When conventional fibreoptic intubation (without the use of the laryngeal mask) was attempted, there was resistance in advancing the tube over the fibrescope in 11 of 20 patients (55%). In contrast, when the laryngeal mask was used for tracheal intubation over the fibrescope, intubation was always smooth. In addition, the time for insertion of the fibrescope into the trachea was a few seconds shorter with the use of the laryngeal mask than without, although the total time was a few seconds longer because of the time taken to insert the mask.50
Intubating laryngeal mask airway
There have been several reports of successful intubation through the intubating laryngeal mask after failed or previously difficult fibreoptic tracheal intubation.11 35 47 53 86 One study has shown that, as with the classic laryngeal mask, the intubating laryngeal mask facilitates fibreoptic intubation. In that study, conventional fibreoptic intubation was easy in only 14 of 42 patients (33%), whereas fibreoptic intubation through the intubating laryngeal mask was easy in 27 of 42 patients (64%).5 The time for tracheal intubation over the fibrescope was significantly shorter with the use of the intubating laryngeal mask than without it.5
In one report of 57 patients with difficult airways in whom fibreoptic intubation through the intubating laryngeal mask was attempted, it was successful in all patients.35 In another study of 100 patients with anticipated difficult intubation, fibreoptic intubation with and without the use of the intubating laryngeal mask was studied. The success rate and time for intubation were similar for the two methods, but complications (such as bleeding or hypoxia) were significantly lower with the use of the intubating laryngeal mask.53 In these two studies, the ease of passing the tube over a fibrescope was not specifically mentioned.
The intubating laryngeal mask may be particularly useful when movement of the patients neck is restricted. In one study in which the patients neck was stabilized by the manual in-line method, and when conventional fibreoptic intubation was attempted, a fibrescope could be inserted into the trachea within 2 min in only eight of 20 patients (40%).5 In contrast, when a fibrescope was inserted through the intubating laryngeal mask, it was possible to insert the fibrescope into the trachea in 19 of 20 patients (95%). Passing a tracheal tube over a fibrescope was also markedly easier with the use of the intubating laryngeal mask than without it. Intubation was easy in four of 20 patients (20%) without the use of the laryngeal mask, whereas it was easy in 13 of 20 patients (65%) with its use.5 In one report of 20 patients with unstable necks, fibreoptic intubation through the intubating laryngeal mask was successful in all patients.12
The trachea can be intubated blindly through the intubating laryngeal mask with a high success rate,21 35 and in patients with difficult airways the rate was similar to, or even greater than, that in patients with normal airways.21 Therefore, it is conceivable that fibreoptic intubation may become easier by using the intubating laryngeal mask in patients with difficult airways. Nevertheless, it has not been confirmed that the intubating laryngeal mask makes the passage of a tube over a fibrescope easier in this group.
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Conclusions |
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To decrease the likelihood of difficulty, we recommend taking the following measurements routinely. Use a thick fibrescope and a thin tracheal tube, such as one with an internal diameter of 6.0 mm. A flexible tracheal tube (or Parker Flex-Tip tube) should be used. Before attempting intubation, the tube should be loaded over the fibrescope to prevent the fibrescope inadvertently passing through the Murphy eye of the tube. The laryngeal mask airway or the intubating laryngeal mask airway may be inserted to facilitate fibreoptic intubation.
Once the fibrescope has been inserted into the trachea, any airway intubator should be removed. When there is difficulty in advancing a tube, withdraw the tube for a few centimetres, rotate it 90° anticlockwise (when a bevelled tube is used), and re-advance it. When advancing the tube, the view through the fibrescope should be monitored continuously, either by a second person or by viewing it on a video screen. If it is still difficult to advance the tube it may be rotated by 180°, and the position of the head and neck adjusted, cricoid pressure applied, or a laryngoscope inserted before another attempt at intubation is made. If it is still difficult, repetitive attempts should be avoided and other options, including avoidance of tracheal intubation or cancellation of surgery, should be considered.
Although the causes of difficulty in tracheal intubation over a fibrescope and the inefficacy of each solution have not been elucidated fully, it is essential at least to choose an appropriate fibrescope and tracheal tube and to apply appropriate manoeuvres, to make fibreoptic intubation safer.
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References |
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