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GENERAL ARTICLES

A Clinical Comparison of the Flexiblade^TM and Macintosh Laryngoscopes for Laryngeal Exposure in Anesthetized Adults

Rochelle W. W. Cheung, MB, BS (Hong Kong), FANZCA, FHKCA, FHKAM^*, Michael G. Irwin, MB, ChB, MD, DA, FRCA, FHKAM, Bassanio C. W. Law, MB, BS (New South Wales), FANZCA, FHKCA, FHKAM, and C. K. Chan, MB, BS (Hong Kong), FHKCA, FHKAM

*Department of Anaesthesiology, Queen Elizabeth Hospital; Department of Anaesthesiology, University of Hong Kong, Queen Mary Hospital; and Department of Anaesthesiology, Kwong Wah Hospital; and the University of Hong Kong, Hong Kong (SAR), China

Address correspondence and reprint requests to Dr. Rochelle W. W. Cheung, Department of Anaesthesia, 1/F, Block D, Queen Elizabeth Hospital, 30, Gascoigne Road, Kowloon, Hong Kong SAR, China; Professor M. G. Irwin, Room 424, Block K, Queen Mary Hospital, Pokfulam Road, Hong Kong SAR, China. Address e-mail to rochelleww{at}yahoo.com.

	Abstract

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The Flexiblade^TM is a laryngoscope with a flexible blade. To evaluate the efficacy of the Flexiblade^TM compared with the classic Macintosh laryngoscope, we performed a clinical study in 200 paralyzed patients undergoing elective surgery requiring general anesthesia and endotracheal intubation. Direct laryngoscopy was performed with a size 3 Macintosh laryngoscope and the Flexiblade^TM, with and without activation of the lever. The laryngeal views were recorded, without manipulation, according to the Cormack and Lehane classification. No laryngoscopic view obtained by the Macintosh blade was worse than that obtained by the Flexiblade^TM without the lever activated. The Macintosh blade improved 58.5% of non-Grade I views obtained by the Flexiblade^TM with its lever not activated. However, when the Flexiblade^TM lever was activated, 39.6% of non-Grade I views obtained by the Macintosh blade were improved, whereas 84.5% of non-Grade I views obtained by the inactivated Flexiblade^TM were improved. Activating the Flexiblade^TM lever never caused a deterioration of view. In only one case was the view better with the Macintosh blade than that with the activated Flexiblade^TM. We conclude that the Flexiblade^TM, after lever activation, is significantly better than the Macintosh laryngoscope for laryngeal visualization in paralyzed adults (P < 0.0001).

	Introduction

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The size 3 Macintosh laryngoscope is the most commonly used device for direct laryngoscopy in our local hospitals. It consists of a rigid curved blade (available in a range of lengths to accommodate patients of different sizes) with a detachable handle. It is designed to rest in the vallecula and lift the epiglottis to expose the laryngeal inlet. However, when visualization is difficult, the lifting force may have to be increased, possibly resulting in dental and/or oral trauma.

The Flexiblade^TM laryngoscope (Fig. 1) is composed of two parts: a blade with an adjunct lever and a handle. It has been designed to facilitate tracheal intubation when the patient's head is in the neutral position. After insertion into the oral cavity, the concave-shaped tip of the blade enters the vallecula and fits its anatomical shape. By gently squeezing the lever on the handle (Fig. 2), the distal half (between 35 mm and 100 mm from the tip's end) of the blade changes from nearly straight into a curved blade with angles between 9° ± 1° and 30° ± 2° (http://www.arcomedic.com/try.htm). This flexibility allows depression of the tongue and hyo-epiglottic ligament, which, together with forward movement of the epiglottis, is intended to assist visualization of the vocal cords. As a result, the need to lift the mandible anteriorly or change the axis of the laryngoscope in the patient's mouth, such as in a difficult intubation, may be avoided (1,2) Fig. 3.

View larger version (120K): [in this window] [in a new window]   Figure 1. The unactivated FlexibladeTM.

View larger version (130K): [in this window] [in a new window]   Figure 2. The FlexibladeTM with the lever activated to flex the blade.

View larger version (157K): [in this window] [in a new window]   Figure 3. The FlexibladeTM is detachable for cleaning and comes in 3 sizes.

In a previous evaluation of the use of the Flexiblade^TM by Perera et al. (3), it was demonstrated that the view of the larynx obtained with the Flexiblade^TM in the flexed position is better than the view obtained when used in the neutral, unflexed position, with the assumption that the unflexed Flexiblade^TM behaves like a normal Macintosh blade. However, the efficacy of the Flexiblade^TM has not been properly compared with the standard Macintosh laryngoscope.

This study was designed to evaluate the efficacy of the Flexiblade^TM compared with the Macintosh laryngoscope in laryngeal visualization for endotracheal intubation in anesthetized, paralyzed adults.

	Methods

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Local institutional ethics approval was obtained before this study. Two-hundred patients, aged 18 to 65 yr old, ASA physical status I–III, undergoing elective surgery requiring general anesthesia, muscle relaxation, and endotracheal intubation, were enrolled. All patients had their airways examined preoperatively using combinations of mouth opening, the modified Mallampati score, anterior jaw movement, and cervical spine movement (4,5). Those with a history of airway difficulties, known or suspected cervical spine pathology, mouth opening of <4 cm, Mallampati grade IV, patients requiring rapid sequence induction of anesthesia, and those who refused were excluded. Written informed consent was obtained in all cases.

On arrival in the operating room, patients were positioned in the "sniffing" position with one standardized pillow under their head. Monitoring consisted of electrocardiograph, noninvasive arterial blood pressure, pulse oximetry and peripheral nerve stimulation of the ulnar nerve at the wrist (AS/3; Datex-Engstrom, Helsinki, Finland). An IV cannula was inserted. Patients received oxygen for 3 min before IV induction of anesthesia, consisting of fentanyl 1–2 µg/kg, thiopentone 3–5 mg/kg, and cisatracurium 0.15 mg/kg for muscle relaxation. Patients' lungs were then ventilated manually via a facemask with nitrous oxide in oxygen with isoflurane until muscle paralysis was complete as shown by no twitches from a train-of-four stimulus (60 Hz, 50 mA).

At this time, direct laryngoscopy was performed, using the size 3 Macintosh laryngoscope and the smallest Flexiblade^TM (similar to the Macintosh size 3; Fig. 3). The order of blade used was randomized by a computer-generated list. The laryngoscopy view was noted using the Cormack and Lehane classification (6). Grade I: Full view of the glottis obtained; Grade II: only the posterior commissure of the glottis seen; Grade III: only the epiglottis seen; Grade IV: even the epiglottis could not be seen.

In the case of the Flexiblade^TM, the laryngoscopy view was recorded before and after activation of the lever. No laryngeal manipulation was attempted to improve the larynogoscopic view during grading.

After laryngoscopy had been performed with both blades, endotracheal intubation took place, using the latter blade. Anterior laryngeal pressure, e.g., backward, upward, and to the right pressure (BURP) (7), and devices assisting intubation (e.g., gum elastic bougie) (8) were used, if necessary, to facilitate intubation. Any complications associated with the use of the laryngoscopes, such as dental injury and oral trauma, were recorded. Surgery was then allowed to proceed as normal. Patients were informed if laryngoscopy or intubation was difficult.

The SAS System for Windows Release 9.1 (SAS Institute Inc., Cary, NC) was used for statistical analysis. Demographic data were analyzed by Student's t-test, ² test, and Mann-Whitney U-test. The laryngoscopic view data were analyzed using Bowker's test of symmetry and ² test. The intubation and complication data were analyzed by ² test or ² with continuity correction. A P value of < 0.05 was regarded as statistically significant.

	Results

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There were 63 male and 137 female patients studied. One patient with a history of nasopharyngeal carcinoma treated with radiotherapy, resultant in limited mouth opening and neck movement, was excluded from the study. Patients were divided into 2 groups: Group 1 had direct laryngoscopy performed using the Macintosh laryngoscope first and then the Flexiblade^TM without activating the lever, followed by the Flexiblade^TM with lever activation. Group 2 had direct laryngoscopy performed by the Flexiblade^TM first without activation of the lever, then with activation of the lever, and finally with the Macintosh laryngoscope. The demographic data were compared as shown in Table 1, with no significant difference seen between the 2 groups.

The laryngoscopic views obtained with the Macintosh laryngoscope and Flexiblade^TM before and after activation of the lever are shown in Tables 2–4. The views obtained from the two sequence groups were consistent. No view obtained with the Macintosh laryngoscope was worse than that obtained using the Flexiblade^TM before activation of the lever in both groups. In contrast, 83 views (41.5%) obtained with the Flexiblade^TM before activation of the lever were worse than those obtained with the Macintosh laryngoscope. Therefore, the laryngoscopic views obtained with the Macintosh laryngoscope were significantly better than the Flexiblade^TM before lever activation (P < 0.0001, Bowker's test).

Activating the Flexiblade^TM lever did not worsen the laryngoscopic view in any patient in both groups (Table 4). It did, however, result in an improvement in 120 subjects (60%). Therefore, the laryngoscopic views obtained with the Flexiblade^TM after lever activation were significantly better than before activation (P < 0.0001, Bowker's test).

A summary of the view improvement among the 3 different laryngoscopes is shown in Table 5. The Macintosh laryngoscope improved 58.5% of non-Grade I views obtained by the Flexiblade^TM before lever activation. Activation of the Flexiblade^TM lever improved 39.6% of non-Grade I views obtained using the Macintosh blade and 84.5% of non-Grade I views obtained using the inactivated Flexiblade^TM.

The use of additional manipulation to assist endotracheal intubation was similar in both groups (Table 6). There was 1 case of minor oral abrasion reported during use of the Flexiblade^TM in our study. This was in a patient with Grade III laryngoscopy.

	Discussion

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Successful direct laryngoscopy and, hence, endotracheal intubation, needs elevation of the epiglottis with the laryngoscope blade and, ideally, a clear view of the laryngeal inlet. Various laryngoscope blades have been designed to suit variations in airway anatomy. The Macintosh blade is generally considered best in most adults, whereas the straight blades are useful in those with a long and floppy epiglottis and a small retromandibular space. The levering laryngoscope is designed to lower the fulcrum of direct laryngoscopy to the pharyngeal area, instead of the upper teeth, to reduce the risk of dental trauma.

In our study, each patient acted as his or her own control. Contrary to the postulation of Perera et al. (3), our study showed that the Flexiblade^TM in the neutral position, i.e., with the lever not activated, does not behave like a Macintosh laryngoscope. If the lever of the Flexiblade^TM is not activated, it functions like the straight Miller laryngoscope. Although the straight Flexiblade^TM offers an almost ideal straight view to the vocal cords, it further reduces the small space reserved for the tongue behind the mandible (9). This functional restriction had been implicated in some cases of difficult laryngoscopy and may explain the difference we observed in the laryngoscopy views in our patients when the Macintosh laryngoscope was compared with the Flexiblade^TM without activation of the lever.

The Flexiblade^TM, with the lever activated, facilitated better laryngeal exposure than the Macintosh blade. This may be explained by the design of 6 intermediately located slots in the Flexiblade^TM, which can be reshaped to fit the anatomy of an individual's larynx once the tip of the blade lies in the vallecula. This is done simply by pulling or releasing the control lever on the handle. Such activation can cause as much as 10 cm flexion of the blade, changing its shape and length, as well as various eye line deviations and forward space displacement. It can thus be considered not as a single blade but as a multiblade instrument (9).

In our study, the use of the Flexiblade^TM did not improve the laryngeal view in 22 (16.5%) of the patients. We feel, however, that this may be partly explained by a limitation in the breadth of the Cormack and Lehane classification, such that a slight improvement in exposure was not sufficient to upgrade the view. It is our impression that even though the vocal cords could not be exposed, the use of the Flexiblade^TM, together with activation of the lever and its flexibility, did allow visualization of the arytenoid cartilages, which may therefore help to improve the likelihood of successful endotracheal intubation.

Even with better visualization of the laryngeal inlet, the use of additional maneuvers to facilitate endotracheal intubation did not differ in our groups. Arino et al. (10) have suggested that a good laryngeal view with the intubating device does not equate with ease of intubation. However, as the Flexiblade^TM had just been recently introduced to our institution, we only included patients with no external anatomical features of a difficult airway and, thus, the total number of difficult intubations and requirement for maneuvers to assist intubation was small in our study.

During the study period, there was one case of misassembly of the Flexiblade^TM after cleaning in our institution (11); fortunately this did not result in a mishap. There has also been a case report of breakage of the blade during cleaning, which the manufacturer attributed to handlers not following the instructions for proper management of the blade (12). As the Flexiblade^TM is still a relatively new instrument; clinical experience in using it may further improve its safety in clinical use.

We conclude that the Flexiblade^TM can be used routinely for endotracheal intubation and that it gives a better view of the larynx than a Macintosh laryngoscope. However, the number of Grade III and IV laryngeal views encountered in our study was limited, and further investigation would be required to evaluate its role in difficult intubation, as well as its efficacy, compared with other devices such as the McCoy laryngoscope (13,14).

We thank Ms. J.S.F. Man for her expert advice on the data analysis and statistics.

	Footnotes

 
Supported, in part, by the Departments of Anaesthesiology, Kwong Wah Hospital and The University of Hong Kong, Hong Kong, China.

Accepted for publication August 16, 2005.

	References

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Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999