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Original Article

Does left molar approach to laryngoscopy make difficult intubation easier than the conventional midline approach?

Bozdogan, N.*; Sener, M.*; Bilen, A.*; Turkoz, A.*; Donmez, A.*; Arslan, G.*

Author Information
European Journal of Anaesthesiology: August 2008 - Volume 25 - Issue 8 - p 681-684
doi: 10.1017/S0265021508004110

Abstract

Introduction

Unexpected difficult laryngoscopy or intubation increases morbidity and mortality in anaesthesia practice [1]. In some studies, the frequency of difficult laryngoscopy or intubation varied from 1% to 18%, and intubation fails in 0.05% to 0.35% of patients who have difficult laryngoscopy [2,3]. Depending on the laryngeal views required and the definition of ‘difficult intubation' applied, the incidence of difficult laryngoscopy varies with the pressure application on the larynx and with the use of different blades and techniques [4-7].

There are various methods of predicting difficult intubation, such as the Mallampati classification [8], head–neck motility [4], the measurement of sternomental and thyromental distances [1,2] and the results of the Wilson risk sum [9]. However, those methods may not be sufficient to determine the risk of difficult intubation, and unexpected difficulties in intubation may occur [2]. Recently, left molar approach of laryngoscopy has been reported to make difficult intubation easier [10-13]. We therefore aimed to investigate whether left molar approach of laryngoscopy provided a better laryngeal view than conventional midline approach and made intubation easier for unexpected difficult intubation.

Methods

Informed consent was taken from all patients and approval was obtained from the Ethical Committee (Project No. KA 05/217). Between January 2005 and May 2006, 1386 patients received a general anaesthetic before undergoing endotracheal intubation for surgery. In 20 of those patients, intubation through conventional midline approach failed, but ventilation through a mask was sufficient. Those 20 patients were the subjects in our study. Children, patients with increased intracranial pressure, a poor clinical prognosis, or a history of respiratory distress, and pregnant women were excluded.

First, the patients were monitored with electrocardiogram and pulse oximetry, and their blood pressure was measured. The patients then received oxygen 100% for 3 min, after which anaesthesia was induced with thiopental sodium 5 to 7 mg kg−1 or propofol 2 mg kg−1, vecuronium bromide 0.1 mg kg−1 and fentanyl 1 μg kg−1. Complete muscle relaxation occurred after 4 min. Then, when the patient's head and neck were in hyperextension, we used a number 3 or 4 Macintosh blade and the conventional midline approach to perform a laryngoscopic evaluation. The external laryngeal compression was routinely used to improve the laryngeal view. Laryngoscopic evaluation was based on the Cormack–Lehane classification [3] and the best glottic views were recorded. Finally, the 20 patients with Grade III-IV views on laryngoscopic evaluation and in whom conventional midline approach was unsuccessful on the first attempt underwent another laryngoscopy, during which the tongue was displaced to the right side and the laryngoscope was inserted from the left corner of the mouth at a point above the left molars. After the laryngoscopic evaluation had been performed, endotracheal intubation was attempted with external laryngeal compression. If left molar laryngoscopy failed, we performed the conventional midline approach again, and intubation was accomplished with a Miller blade and auxiliary equipments. All laryngoscopic evaluations and endotracheal intubations were made by one of three anaesthesiologists (NB, staff anaesthesiologist with 6 yr experience; MS, assistant professor with 8 yr experience; AB, staff anaesthesiologist with 9 yr experience). The number of intubation attempts and the use of instruments were recorded.

Statistical analyses were performed with SPSS software (Statistical Package for the Social Sciences, v. 11.0, SSPS Inc., Chicago, IL, USA). The laryngoscopic views were compared with Wilcoxon signed rank sum test. The success rate of tracheal intubation was compared with McNemar's test. Data were expressed as the mean ± SD. A P value of less than 0.05 was considered significant.

Results

We had unexpected difficulty in intubating 20 patients (ASA I–III; 2 women and 18 men). Table 1 presents information about the patients.

Table 1
Table 1:
Patient characteristics (n = 20).

Of the 20 patients who experienced unexpected difficult intubation, 18 patients had a Grade III laryngeal view and two patients had a Grade IV laryngeal view according to the Cormack–Lehane classification on the conventional midline approach. Of the 20 patients who experienced unexpected difficult intubation, three of those patients had a Grade I laryngeal view, 11 patients had a Grade II laryngeal view, five patients had a Grade III laryngeal view and one patient had a Grade IV laryngeal view according to the Cormack–Lehane classification on the left molar approach. According to the Cormack–Lehane classification, left molar approach of laryngoscopy (when compared with conventional midline approach) significantly improved the laryngeal view (P < 0.01, Table 2). Laryngoscopic view was improved in 14 patients in Grade III and in one patient in Grade IV with the left molar approach. The number of patients with better view was 15.

Table 2
Table 2:
Laryngoscopic views of the patients with unexpected difficult intubation (Cormack-Lehane Classification [3]).

We intubated 11 patients with laryngeal view Grade I (three patients) and Grade II (eight patients) on the left molar approach on our first attempt (Table 2). Left molar approach of laryngoscopy improved not only laryngeal view but also the success rate of tracheal intubation (P < 0.01 with the Yates correction factor).

In all, nine patients who could not be intubated with the left molar approach of laryngoscopy underwent the conventional midline approach again. Using a Miller blade, a stylet and by applying external pressure to the larynx, we were able to perform intubation after multiple (three to five) attempts. None of the nine patients who could not be intubated with the left molar approach of laryngoscopy required fibreoptic bronchoscopy, retrograde intubation or additional techniques.

Discussion

Many tests and evaluation criteria used to predict difficult intubation yield inconclusive results, and difficult intubation can occur unexpectedly in patients who have received a general anaesthetic [2]. After failed intubation in patients who have received a general anaesthetic, the following techniques are recommended in the presence of adequate mask ventilation: using different blades, blind oral or nasal intubation, stylet-assisted intubation, fiberoptic intubation, Airway Scope (Pentax Corporation, Tokyo, Japan), video laryngoscope, retrograde intubation, placing the laryngeal mask airway or tracheostomy [14-17]. In recent years, it has been reported that the left molar approach for laryngoscopy can be useful because it may improve the laryngeal view [10-13]. We suggest that this should be the method of choice in cases of difficult intubation and can be attempted until preparations for alternate airway management are completed. Left molar approach of laryngoscopy is an easy and simple procedure, the performance of which does not require additional equipment.

The tracheas of three patients could not be intubated even though the laryngeal view was Grade II with the left molar approach. The light of a laryngoscope blade is routinely on the right side and, unlike the conventional approach, left-sided laryngoscopy requires that the tongue be displaced to the right. The reason for failed intubation in these cases was due to the tongue being displaced to the right, which may prevent tracheal intubation. Thus improved laryngeal view does not necessarily mean improved success rate of tracheal intubation.

In their series of 1015 patients, Yamamoto and colleagues [10] reported that the left molar approaches provided a better laryngeal view than did the conventional midline approach. Those authors performed endotracheal intubation via the left molar approach of laryngoscopy in 13 of 20 patients in whom intubation was difficult. They explained that when a Macintosh blade was inserted from a point above the left molars, the glottic view improved and the blade facilitated quick and atraumatic laryngoscopy. They added that the Macintosh blade deviated less from the ideal line than did the Miller blade, but that even when the Macintosh blade was used and an optimum jaw-head position was achieved, a good glottic view (which would facilitate intubation) sometimes could not be attained [10]. We also performed laryngoscopy with a Macintosh blade in 20 patients in whom intubation was difficult. We changed that blade and preferred a Miller blade for use in patients in whom the left molar approach of laryngoscopy had failed. Of the 20 patients who could not be intubated with the conventional midline approach on the first attempt, 11 underwent left molar approach of laryngoscopy and nine underwent a second conventional midline approach in which a Miller blade and a stylet were used. The results of our study are consistent with those of a study by Yamamoto and colleagues [10].

Similar cases of difficult intubation have been reported in the literature. Mentzelopoulos and colleagues [12] used a McCoy balloon laryngoscope and the left molar approach of laryngoscopy to achieve intubation in patients with endotracheal arthrogryposis multiplex congenita and a history of difficult intubation. Sato and Shingu [13] applied the left molar approach to a patient with fragile (mobile) upper incisor. They reported that the left molar approach of laryngoscopy provided a better laryngeal view than did the conventional midline approach for laryngoscopy that was routinely used in their practice [13]. Farley and colleagues [11] also performed the left molar approach of laryngoscopy and obtained a better laryngeal view after they failed to achieve a good laryngeal view via the fiberoptic bronchoscope-assisted standard approach in a case of difficult intubation. The left molar approach of laryngoscopy is preferred in the presence of a wound or infected lesion on the right side of the mouth or the lips [13].

We conclude that the left molar approach of laryngoscopy can be used in cases of unexpected difficult intubation with a high degree of success while preparations of other intubation devices are made, e.g. laryngeal mask, a fiberoptic bronchoscope, jet ventilation or retrograde catheter.

Acknowledgements

The study was supported by Research Council of Başkent University Faculty of Medicine (Project no. KA05/217). This paper was presented as a poster at the 39th Congress of the Turkish Anesthesiology and Intensive Care Society on October 25–29, 2005, Antalya, Turkey. The authors have no conflicts of interest that are directly relevant to the content of this manuscript.

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Keywords:

INTUBATION INTRATRACHEAL, technique; LARYNGOSCOPES, Macintosh; LARYNX

© 2008 European Society of Anaesthesiology