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Canadian Journal of Anesthesia 47:843-848 (2000)
© Canadian Anesthesiologists' Society, 2000
Reports of Investigation

Intubating laryngeal mask for fibreoptic intubation - particularly useful during neck stabilization

Takashi Asai, MD PhD, Yoshitaka Eguchi, MD, Kohei Murao, MD, Tateki Niitsu, MD and Koh Shingu, MD

From the Department of Anesthesiology, Kansai Medical University, Osaka, Japan.

Address correspondence to: Takashi Asai MD PhD, Department of Anesthesiology, Kansai Medical University, 10-15 Fumizono-cho, Moriguchi City, Osaka, 570-8507, Japan. Phone: 81-6-992-1001; Fax: 81-6-991-1301; E-mail: asait{at}takii.kmu.ac.jp


   Abstract
TOP
 Abstract
Introduction
 Patients and Methods
 Results
 Discussion
 References
 
Purpose: To assess the ease of fibrescope-assisted tracheal intubation while the patient's head and neck were placed in the neutral or the manual in-line position, and to determine if the intubating laryngeal mask facilitated fibreoptic intubation in these positions.

Methods: In 84 patients, the patient's head and neck were placed in the neutral position (pillow placed under occiput), and in another 40 patients the head and neck were stabilized by the manual in-line method (no pillows under occiput). In both groups, after induction of anesthesia with 2.0 - 2.5 mg•kg–1 propofol, 50 – -100 µg fentanyl and 1.0 mg·kg–1 vecuronium, patients were allocated randomly into two groups: in Group C tracheal intubation was attempted using only a fibrescope, whereas in Group L fibreoptic intubation through the intubating laryngeal mask was attempted.

Results: In group C the success rate of fibreoptic tracheal intubation within two minutes was higher in the neutral position (31 of 42 patients (73%)) than in the manual in-line position (8 of 20 patients (40%)). In contrast, in group L the success rate was similar between the two positions. Tracheal intubation was easier in group L than in group C (P < 0.01 or 0.001) and the time for intubation was shorter in group L than in group C in both head and neck positions.

Conclusions: Fibreoptic tracheal intubation was more difficult in the manual in-line position than in the neutral position. The intubating laryngeal mask facilitated fibreoptic intubation in both positions.


   Introduction
TOP
 Abstract
 Introduction
Patients and Methods
 Results
 Discussion
 References
 
THE fibreoptic bronchoscope is useful to facilitate tracheal intubation in patients with difficult airways, but it may be difficult to advance a tracheal tube over the fibrescope in 40 – 90% of cases.1–5 This difficulty depends on the size of the fibrescope and tracheal tube: the larger tracheal tube (or greater the gap between a fibrescope and tracheal tube), the greater the difficulty in passing the tube over the fibrescope.1,2 The position of the patient's head and neck may also alter the ease of fibrescope-aided tracheal intubation. For example, a restricted movement of the head and neck either by pathological changes or by active stabilization may make location of the glottis using the fibrescope more difficult. Although a fibreoptic bronchoscope has been considered to be useful for tracheal intubation in these circumstances, there have been no reports of the ease and success rate of fibreoptic tracheal intubation during stabilization of the head and neck.

The intubating laryngeal mask is useful in facilitating tracheal intubation,6–9 but its success rate at the first attempt can be as low as 50% when the tube is advanced blindly.6 The use of the fibrescope should increase the success rate of intubation, but there have been only a few studies of this method7,8 and none compared the ease of fibreoptic tracheal intubation with and without the use of the intubating laryngeal mask.

The main aims of our study were to determine (1) if the intubating laryngeal mask facilitated fibreoptic tracheal intubation in patients with normal head and neck movement, (2) the ease of a fibrescope-aided tracheal intubation during the manual in-line stabilization of the head and neck, and (3) if the intubating laryngeal mask has a role in fibreoptic intubation in the patient with restricted neck movement.


   Patients and Methods
TOP
 Abstract
 Introduction
 Patients and Methods
Results
 Discussion
 References
 
After obtaining institutional research ethics committee approval and written informed consent, we studied 124 patients, ASA physical status 1 or 2, aged 18 – -75 yr, undergoing elective surgery. Patients were excluded if they had pathology of the neck, upper respiratory or alimentary tracts, if they were at risk of pulmonary aspiration of gastric contents or if difficult tracheal intubation or ventilation was predicted. Patients with Mallampati class 3 or 410,11 were also excluded. Diazepam, 5 mg po, was given on the night before anesthesia; no antisialagogues were given.

Phase 1—Neutral head and neck position
In the first set of 84 patients, tracheal intubation was attempted while the patient's head, but not the neck, was placed on a firm pad (approximately 7 cm in height). This head and neck position was arbitrarily defined as the neutral position. Anesthesia was induced with 2.0 – -2.5 mg·kg–1 propofol, 50 – -100 µg fentanyl and 1.0 mg·kg–1 vecuronium, and was maintained with sevoflurane in oxygen. The patients were then allocated randomly into two groups, using block randomization (in blocks of 12). In one group (control group or Group C), tracheal intubation was attempted using only a fibreoptic bronchoscope, whereas in the other group (Group L), fibreoptic intubation through the intubating laryngeal mask was attempted. In both groups, a fibrescope with an outer diameter of 3.5 mm was used. We used a Mallinckrodt reinforced tracheal tube (Athlone, Ireland), since the specially tailored tube (Euromedical, Kadal, Malasia) for the intubating laryngeal mask was not available at our hospital, and since the Mallinckrodt tube has been considered to be suitable for this purpose.1 The connector of the Mallinckrodt tube is glued to the tube so that it is not possible to remove the laryngeal mask after tracheal intubation; therefore, the connector was detached from the tube using a blunt spatula before insertion.12 A 7.0-mm ID tracheal tube was used in women and an 8.0-mm ID tube in men. In group L, the laryngeal mask was removed after completion of the study.

In group C, tracheal intubation was attempted using the method described previously,1 except that no attempts were made to extend the head on the neck. After neuromuscular blockade had been obtained, the jaw was pulled forward by an assistant. The fibrescope, which was passed through a tracheal tube, was inserted orally into the trachea and the tube was passed over it. No airway intubator was used.

In group L, the intubating laryngeal mask was inserted using the method described by Brain et al.6 A size # 5 was used in men and a # 4 in women unless it was judged to be too large when one size smaller was used. If ventilation was inadequate, another attempt at insertion was made. A tracheal tube was inserted into the laryngeal mask, the fibrescope was passed through these into the trachea, and the tracheal tube was passed over the fibrescope.

In both groups, if it was difficult to intubate the trachea, rotation of the tube or maneuvering of the patient's head and neck was allowed. In group L, adjusting the position of the laryngeal mask using the metal guiding handle6 was allowed. Only one attempt, two minutes for insertion of the fibrescope and two minutes for tracheal intubation over the fibrescope, was allowed for tracheal intubation. The ease of tracheal intubation was assessed and scored in four grades:1 ‘Optimal&': no collision (hold-up) encountered; ‘Suboptimal&': hold-up, relieved by rotation of the tube once; ‘Difficult&': hold-up, requiring more than one rotation of the tube, alteration in the patient's head or neck position or maneuvering the metal handle of the intubating laryngeal mask; and ‘Failure&': failure of the attempt at fibreoptic tracheal intubation within the above time limits.

In patients in whom tracheal intubation was successful, the time from removal of the facemask to insertion of the fibrescope into the trachea, and the time from the insertion of the fibrescope to connection of the breathing system after successful tracheal intubation, were measured. In group L, the time from removal of the facemask to insertion of the fibrescope into the trachea was the sum of the time taken for insertion of the laryngeal mask and time to insertion of the fibrescope. When insertion of the laryngeal mask failed at the first attempt, but succeeded at the second attempt, the sum of the times taken for the first and the second attempts was recorded.1

Phase 2—Manual in-line position
In the second set of 40 patients, tracheal intubation was attempted while the patient's head and neck were stabilized. Pillows were removed and the patient's head and neck stabilized by an assistant who held the sides of the neck and the mastoid processes (manual in-line stabilization).

After induction of anesthesia and neuromuscular relaxation, the patients were allocated randomly into two groups, and either tracheal intubation using a fibreoptic bronchoscope (Group C) or fibreoptic intubation through the intubating laryngeal mask (Group L) was attempted. The procedures were the same as in Phase 1.

Statistical analysis
Chi-squared for trend was used to compare the ease of tracheal intubation between groups. P values < 0.05 were considered significant. The 95% confidence intervals (CI) for the difference in the success rate of intubation, in the proportion of the ‘Optimal&' intubation, and in median time between the groups were calculated.

For the Phase 1 study, the reported proportion of the Optimal intubation using an 8.0 mm ID tracheal tube (without the use of the laryngeal mask) is up to 20%.1–3 We considered that a method which would increase the proportion by 30% to be clinically important. To detect this difference, with a power of 80%, 84 patients would be required. For the Phase 2 study, a preliminary study indicated that fibrescopy in group C might often fail, and the success rate would be 50% or less. We considered that a method which would increase the success rate to 90% to be clinically important. To detect this difference (40% or greater), with a power of 80%, 40 patients would be required.


   Results
TOP
 Abstract
 Introduction
 Patients and Methods
 Results
Discussion
 References
 
The patients' characteristics were similar between the groups in Phase 1, whereas in Phase 2 body weight in group C was somewhat heavier than in group L, possibly due to a greater proportion of men in group C (Table IGo).


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  		TABLE I Patient characteristics (mean ± SD for the age and weight). Group C: conventional fibreoptic tracheal intubation (without the use of the intubating laryngeal mask); Group L: fibreoptic tracheal intubation through the intubating laryngeal mask.
 
Neutral head and neck position
When the patient's head and neck were placed in the neutral position, it was possible to insert the fibrescope into the trachea in 37 of 42 patients (88%) in group C. In group L, insertion of the intubating laryngeal mask was always successful at the first attempt. Fibrescopy through the laryngeal mask succeeded in 38 of 42 patients [90%]).

Tracheal intubation was easier in group L than in group C (P < 0.01) (Table IIGo). The difference in the success rate between groups was 14% (95%CI: -2% – 31%) and in the optimal intubation grade was 31% (95%CI: 12% – 51%).


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  		TABLE II Ease of tracheal intubation over the fibrescope (number of patients (%)). Only one attempt, two minutes for insertion of the fibrescope and two minutes for tracheal intubation over the fibrescope, was allowed for tracheal intubation. There is a significant difference in the ease of tracheal intubation with and without the use of the intubating laryngeal mask during the neutral head and neck position (P < 0.01) and for the manual in-line position (P < 0.001). Group C: conventional fibreoptic tracheal intubation (without the use of the intubating laryngeal mask); Group L: fibreoptic tracheal intubation through the intubating laryngeal mask.
 
In patients in whom tracheal intubation was successful, 95% CI of differences indicated that there was no marked difference between groups in the time for inserting a fibrescope into the trachea, whereas the time for tracheal intubation over the fibrescope was significantly shorter in group L than in group C (Table IIIGo). The median difference for total time for tracheal intubation (from removal of a facemask to connection of the breathing system after tracheal intubation) between groups was 7 sec (95%CI: -2.0 sec— 20 sec).


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  		TABLE III Time (s) for tracheal intubation (median (range)) in whom tracheal intubation succeeded. T1: time from removal of a facemask to insertion of a fibrescope into the trachea; T2: time from insertion of the fibrescope into the trachea to connection of the breathing system after tracheal intubation. Group C: conventional fibreoptic tracheal intubation (without the use of the intubating laryngeal mask); Group L: fibreoptic tracheal intubation through the intubating laryngeal mask.
 
Manual in-line position
When the patient's head and neck were stabilized by the manual in-line method, the fibrescope could be inserted into the trachea within two minutes in only eight of 20 patients (40%) in group C. In group L, the intubating laryngeal mask could be inserted at the first attempt in 19 patients and the remaining one at the second attempt. Fibrescopy through the laryngeal mask succeeded in 19 of 20 patients [95%]).

Tracheal intubation was easier in group L than in group C (P < 0.001) (Table IIGo). The difference between groups in the success rate was 55% (95%CI: 32% – 78%) and in the optimal intubation grade was 45% (95%CI: 18% – 72%).

In patients in whom tracheal intubation succeeded, 95% CI of differences indicated that both time for inserting a fibrescope into the trachea and time for tracheal intubation over the fibrescope were shorter in group L than in group C (Table IIIGo).

Neutral vs Manual in-line positions
When attempts were made to insert the fibrescope into the trachea (without the use of the intubating laryngeal mask), the success rate of fibrescopy was markedly lower during the manual in-line stabilization than during the neutral head and neck position, with a difference of 44% (95%CI: 24% — 72%). As a consequence, the success rate of tracheal intubation was markedly lower during manual in-line stabilization (8 of 20 patients (40%)) than during the neutral head and neck position (31 of 42 patients (73%)). In contrast, when the intubating laryngeal mask was used, there were no marked difference in the success rate of fibrescopy (difference: 4.5%; 95%CI: -8% — 17.5%) and of tracheal intubation (difference: 7%; 95%CI: -7% — 21%) between the two head and neck positions.


   Discussion
TOP
 Abstract
 Introduction
 Patients and Methods
 Results
 Discussion
References
 
We have found that the intubating laryngeal mask facilitated fibreoptic tracheal intubation, fibreoptic intubation (without the use of the intubating laryngeal mask) was often difficult during manual in-line head and neck stabilization, and the intubating laryngeal mask has a potential role in fibreoptic intubation with the patient with restricted neck movement.

Fibreoptic tracheal intubation was easier and faster with the use of the intubating laryngeal mask airway. The success rate of fibreoptic tracheal intubation through the intubating laryngeal mask at the first attempt (37 of 42 patients (88%)) in our study was similar to that in previous studies using the intubating laryngeal mask7,8 and using the conventional laryngeal mask (90% to 95%).1,13 Previous studies have reported that, when tracheal intubation was attempted blindly through the intubating laryngeal mask the success rate was high (93-100%).8,9,14 However, this blind intubation may fail in 50-60% of patients at the first attempt8,9,14 and might damage the larynx and surrounding tissues, such as impingement of the epiglottis into the laryngeal inlet15 or perforation of a esophageal pouch.16 Therefore, caution is required for the blind technique,17 particularly when there is resistance during the advancement of a tracheal tube or when ventilation via the mask is suboptimal. Therefore, we recommend the use of a fibrescope whenever it is available.

Although the success rate of fibreoptic intubation through the intubating laryngeal mask was high, some difficulty was encountered during tracheal intubation in 15 of 42 patients (36%), even when the patient's head and neck were placed in the optimal neutral position. In contrast, when the conventional laryngeal mask was used, tracheal intubation was easy in most patients.1 The reason for this discrepancy is not clear. One possibility is that a larger tracheal tube (7.0-mm ID in men and 8.0-mm ID in women) was used for the intubating laryngeal mask than for a laryngeal mask (6.0-mm ID). It is not known if there is a significant difference in the ease of tracheal intubation between a larger tube and a smaller tube through the intubating laryngeal mask.

Another possibility for the difficulty in tracheal intubation through the intubating laryngeal mask was difficulty in advancing the fibrescope beyond the aperture of the mask. For example, when the epiglottis partially obstructs the aperture of the mask, it is sometimes possible to advance a fibrescope through the conventional laryngeal mask into the trachea, whereas insertion of the fibrescope through the intubating laryngeal mask may be difficult if the downfolded epiglottis prevents lifting the ‘epiglottic elevating bar&'. In fact, it was sometimes necessary to maneuver the metal handle of the laryngeal mask to shift the position of the epiglottis to advance the fibrescope beyond the bar.

The ease of insertion of the fibrescope into the trachea (without the use of the intubating laryngeal mask) was markedly altered by the patient's head and neck position: fibrescopy was much more difficult during the manual in-line position than during the neutral position (Table IGo). One study has shown that placement of a pillow under the patient's head opens the oropharynx.18 In addition, chin lift, thrusting the jaw forward or extension of the head also widens the oropharyngeal space.19,20 In our patients, during the manual in-line position, it was often difficult to advance the fibrescope through the space between the epiglottis and posterior pharyngeal wall, and it was possible to insert the fibrescope into the trachea within two minutes in only eight of 20 patients.

When the intubating laryngeal mask was used, there were no marked differences between the neutral and manual in-line positions in the ease of fibrescopy and tracheal intubation (Table IGo). This is consistent with previous reports of successful intubation through the intubating laryngeal mask after failed or previously difficult fibreoptic tracheal intubation.21–23 In addition, the success rate of blind intubation through the intubating laryngeal mask in patients with difficult airways was similar to, or even greater than, that in patients with normal airways.6 This may indicate that when the intubating laryngeal mask is inserted successfully, factors producing a "difficult airway" (e.g. restricted head and neck position) may often not markedly reduce the ease of fibrescopy and subsequent tracheal intubation.

Accepted for publication June 12, 2000.


   References
TOP
 Abstract
 Introduction
 Patients and Methods
 Results
 Discussion
 References
 
1 Koga K, Asai T, Latto IP, Vaughan RS. Effect of the size of a tracheal tube and the efficacy of the use of the laryngeal mask for fibrescope-aided tracheal intubation. Anaesthesia 1997; 52: 131–5.[Medline]

2 Marsh NJ. Easier fiberoptic intubations (Letter). Anesthesiology 1992; 76: 860–1.[Medline]

3 Schwartz D, Johnson C, Roberts J. A maneuver to facilitate flexible fiberoptic intubation (Letter). Anesthesiology 1989; 71: 470–1.[Medline]

4 Ovassapian A, Yelich SJ, Dykes MHM, Brunner EE. Fiberoptic nasotracheal intubation - incidence and causes of failure. Anesth Analg 1983; 62: 692–5.[Free Full Text]

5 Hakala P, Randell T, Valli H. Comparison between tracheal tubes for orotracheal fibreoptic intubation. Br J Anaesth 1999; 82: 135–6.[Abstract/Free Full Text]

6 Brain AIJ, Verghese C, Addy EV, Kapila A, Brimacombe J. The intubating laryngeal mask. II: a preliminary clinical report of a new means of intubating the trachea. Br J Anaesth 1997; 79: 704–9.[Abstract/Free Full Text]

7 Joo HS, Rose DK. The intubating laryngeal mask airway with and without fiberoptic guidance. Anesth Analg 1999; 88: 662–6.[Abstract/Free Full Text]

8 Asai T, Murao K, Tsutsumi T, Shingu K. Ease of tracheal intubation through the intubating laryngeal mask during manual in-line head and neck stabilisation. Anaesthesia 2000; 55: 82–5.[Medline]

9 Kapila A, Addy EV, Verghese C, Brain AIJ. The intubating laryngeal mask airway: an initial assessment of performance. Br J Anaesth 1997; 79: 710–3.[Abstract/Free Full Text]

10 Mallampati SR, Gatt SP, Gugino LD, et al. A clinical sign to predict difficult tracheal intubation: a prospective study. Can Anaesth Soc J 1985; 32: 429–34.[Medline]

11 Samsoon GLT, Young JRB. Difficult tracheal intubation: a retrospective study. Anaesthesia 1987; 42: 487–90.[Medline]

12 Asai T. Mallinckrodt reinforced tube for tracheal intubation through the intubating laryngeal mask (Letter). Can J Anaesth 1998; 45: 1221–2.[Free Full Text]

13 Asai T, Barclay K, Power I, Vaughan RS. Cricoid pressure impedes placement of the laryngeal mask airway and subsequent tracheal intubation through the mask. Br J Anaesth 1994; 72: 47–51.[Abstract/Free Full Text]

14 Agrò F, Brimacombe J, Carassiti M, Marchionni L, Morelli A, Cataldo R. The intubating laryngeal mask. Clinical appraisal of ventilation and blind tracheal intubation in 110 patients. Anaesthesia 1998; 53: 1084–90.[Medline]

15 Takenaka I, Aoyama K, Nagaoka E, Seto A, Niijima K, Kadoya T. Malposition of the epiglottis after tracheal intubation via the intubating laryngeal mask. Br J Anaesth 1999; 83: 962–3.[Abstract/Free Full Text]

16 Branthwaite MA. An unexpected complication of the intubating laryngeal mask. Anaesthesia 1999; 54: 166–71.[Medline]

17 Asai T, Vaughan RS. Misuse of the laryngeal mask airway (Editorial). Anaesthesia 1994; 49: 467–9.[Medline]

18 Boidin MP. Airway patency in the unconscious patient. Br J Anaesth 1985; 57: 306–10.[Abstract/Free Full Text]

19 Reber A, Wetzel SG, Schnabel K, Bongartz G, Frei FJ. Effect of combined mouth closure and chin lift on upper airway dimensions during routine magnetic resonance imaging in pediatric patients sedated with propofol. Anesthesiology 1999; 90: 1617–23.[Medline]

20 Sivarajan M, Joy JV. Effects of general anesthesia and paralysis on upper airway changes due to head position in humans. Anesthesiology 1996; 85: 787–93.[Medline]

21 Asai T, Shingu K. Tracheal intubation through the intubating laryngeal mask in a patient with a fixed flexed neck and deviated larynx. Anaesthesia 1998; 53: 1199–201.[Medline]

22 Joo H, Rose K. Fastrach—a new intubating laryngeal mask airway: successful use in patients with difficult airways. Can J Anaesth 1998; 45: 253–6.[Abstract]

23 Watson NC, Hokanson M, Maltby JR, Todesco JM. The intubating laryngeal mask airway in failed fibreoptic intubation. Can J Anaesth 1999; 46: 376–8.[Abstract/Free Full Text]




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