Randomized evaluation of the performance of single-use laryngoscopes in simulated easy and difficult intubation

S. J. Twigg*, B. McCormick and T. M. Cook

Royal United Hospital, Combe Park, Bath BA1 3NG, UK*Corresponding author. E-mail: steve.twigg@lineone.net

{dagger} Presented at 35th Annual Scientific Meeting of Group of Anaesthetists in Training (GAT), June 2002, as part of the registrar’s prize competition.
{ddagger} This article is accompanied by Editorial I.

Accepted for publication: June 26, 2002


    Abstract
 Top
 Abstract
 Introduction
 Material and methods
 Results
 Discussion
 References
 
Background. Single-use laryngoscopes are becoming used more widely.

Methods. We compared six types of single-use laryngoscope with the standard Macintosh laryngoscope using the Laerdal SimManTM patient simulator. Twenty anaesthetists attempted to intubate the simulator with standardized airway settings allowing a full view of the vocal cords (‘easy intubation’). The airway settings were then changed so that only the posterior part of the glottis was visible (‘difficult intubation’) and the anaesthetists were asked to intubate the simulator again.

Results. The time to intubate with the standard laryngoscope was less in both easy (P<0.05) and difficult (P<0.01) intubations. The performance of five laryngoscopes during easy intubation (P<0.01) and four during difficult intubation (P<0.001) was significantly worse than that of the Macintosh. There was a significant difference in Cormack and Lehane grading between the laryngoscopes tested in both easy (P<0.05) and difficult (P<0.05) intubation. The percentage of glottic opening visible (POGO score) also differed between laryngoscopes in both the easy (P<0.01) and difficult (P<0.001) groups. The highest POGO scores were obtained with the Macintosh laryngoscope. During the difficult intubation simulation, the reusable Macintosh laryngoscope needed less use of a bougie and had fewer failed intubations than the single-use laryngoscopes, but these differences did not reach statistical significance.

Conclusions. Of the laryngoscopes tested, the standard reusable Macintosh laryngoscope performed best. The EuropaTM was the best single-use laryngoscope. Some single-use laryngoscopes tested were significantly inferior to the Macintosh. This raises concern over their use in clinical practice, particularly if intubation is difficult.

Br J Anaesth 2003; 90: 8–13

Keywords: complications, prion diseases, Creutzfeldt–Jakob disease; equipment, disposable; equipment, laryngoscopes; infection, cross infection; intubation, tracheal


    Introduction
 Top
 Abstract
 Introduction
 Material and methods
 Results
 Discussion
 References
 
Concerns over the iatrogenic transmission of prion-related diseases from instruments used in the oropharynx have increased the use of single-use laryngoscopes.1 2 There are few published data on the use of single-use laryngoscopes and none on their use in difficult intubations. There have been reports of problems while using single-use laryngoscopes.3 We studied six single-use laryngoscopes and compared them with standard reusable equipment. We used a patient simulator as an airway model to provide standard conditions for laryngoscopy and to assess performance during simulated easy and difficult intubation.


    Material and methods
 Top
 Abstract
 Introduction
 Material and methods
 Results
 Discussion
 References
 
The Laerdal SimManTM patient simulator (Laerdal Medical, Orpington, UK) was used to simulate easy and difficult intubation. To simulate easy intubation, the simulator was used in its basic configuration. For the difficult intubation, the rigid neck and pharyngeal swelling functions were combined. This allowed the posterior part of the glottis to be seen with some difficulty (Cormack and Lehane grade II).4 Any increase in difficulty caused by the equipment would prevent a view of the glottis (grade III view).

Six size 3 Macintosh-type single-use laryngoscopes of different designs, a sheathed Macintosh laryngoscope and a standard Macintosh laryngoscope were tested. Details of the laryngoscopes are given in Table 1, and photographs are provided in Figures 1 and 2. A size 8 Portex cuffed tracheal tube was used for intubation and a gum elastic bougie was available.


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Table 1 Summary of the laryngoscopes studied
 


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Fig 1 The laryngoscopes tested (1). (A) Macintosh. (B) Sheathed Macintosh. (C) Europa. (D) Lite-Blade.

 


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Fig 2 The laryngoscopes tested (2). (A) Optima. (B) Optiscope. (C) Venticaire. (D) Vital View.

 
Twenty anaesthetists, of various grades and experience, were asked to intubate the simulator and confirm placement of the tracheal tube by inflating the chest twice using a self-inflating bag. The anaesthetists each familiarized themselves with the simulator before taking part in the study. They were instructed to use the same intubation technique for each laryngoscopy and to note the best view achieved. Intubators were reminded of the Cormack and Lehane grading and percentage of glottis visible at laryngoscopy (POGO) scoring systems before starting the study, and poster-size illustrations were used to aid classification.

The eight laryngoscopes studied were presented consecutively in a random order generated by picking numbered balls out of a bag. Initially the simulator was set to ‘easy intubation’. Time from picking up the laryngoscope to the second chest inflation was taken as the time to intubate. A maximum of 2 min was allowed, after which time the intubation was classed as failed. Outcome measures were time to complete intubation, grading of view obtained at laryngoscopy after Cormack and Lehane,4 POGO score,5 frequency of use of a gum elastic bougie and failed intubation. The set of eight intubations was then repeated in a new random order with the simulator set to ‘difficult intubation’.

Data were analysed using SPSS (SPSS, Chicago, IL, USA). The time to complete intubation for each laryngoscope was analysed with a Kaplan–Meier survival plot (graphs not shown). For each intubator, the time to complete intubation was ranked according to type of laryngoscope. This ranking was analysed by univariate analysis of variance. Comparison of each laryngoscope with the standard Macintosh laryngoscope was made by post hoc testing with Dunnett’s two-sided t-test, which includes a correction for multiple testing. Cormack and Lehane grading of view at laryngoscopy, use of bougie and number of failed intubations per laryngoscope were analysed with the {chi}2 test. POGO score was compared using the Kruskal–Wallis test. Statistical significance was taken if P<0.05.


    Results
 Top
 Abstract
 Introduction
 Material and methods
 Results
 Discussion
 References
 
Results are presented with the standard Macintosh laryngoscope first, the sheathed Macintosh next and then the single-use laryngoscopes in alphabetical order. The term ‘OptimaTM’ refers to the disposable version of the laryngoscope blade and the term ‘standard Macintosh’ refers to the reusable version (see Table 1).

Time to complete intubation
The median time to complete intubation for each laryngoscope is given in Table 2. There was a significant difference between the laryngoscopes in both the easy (P<0.05) and the difficult airway setting (P<0.01). The single-use laryngoscopes were ranked for each intubator and the rankings were compared with those of the standard Macintosh (Table 3). The standard Macintosh laryngoscope was ranked above all others for both easy and difficult intubation. In the easy intubation group, the Lite-BladeTM, OptimaTM, OptiscopeTM, VenticaireTM and Vital ViewTM all performed significantly worse than the standard Macintosh. In the difficult intubation group, the Vital View, Optima, Venticaire and Optiscope performed significantly worse.


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Table 2 Median time (s) to complete intubation (95% confidence interval)
 

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Table 3 Mean difference in ranked order of laryngoscopes as compared with the standard Macintosh laryngoscope (95% confidence interval) for easy and difficult airway settings
 
Cormack and Lehane grading
For the easy intubation setting all intubations were graded I or II (Table 4) and a significant difference between the laryngoscopes was demonstrated (P<0.05). The highest number of grade I intubations was seen with the standard Macintosh and the Europa laryngoscopes. For the difficult intubation setting, intubations were graded I–IV (Table 4) and a significant difference between the laryngoscopes were also recorded (P<0.05). Again, the best airway scores were obtained with the standard Macintosh and Europa laryngoscopes.


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Table 4 Grading of view at laryngoscopy according to Cormack and Lehane for easy and difficult airway settings. P-values imply significant difference between laryngoscopes for view at laryngoscopy
 
Percentage of glottic opening visible
There was a difference in the POGO scores for the different laryngoscopes in both the easy (Fig. 3, P<0.01) and difficult (Fig. 4, P<0.001) intubation groups. The standard Macintosh and the Europa had the highest POGO scores.



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Fig 3 POGO scores for each laryngoscope for easy airway setting. Central bar, median; box area, interquartile range; whiskers, range.

 


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Fig 4 Median POGO score for each laryngoscope for difficult airway setting. Central bar, median; box area, interquartile range; whiskers, range.

 
Use of gum elastic bougie
A bougie was used on only five occasions for the easy airway setting (data not shown) but was commonly used for the difficult airway setting (Table 5). The differences between laryngoscopes in the frequency of use of the bougie were not statistically significant, but the bougie was used least with the standard Macintosh and the Europa.


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Table 5 Use of gum elastic bougie and number of failed intubations (>120 s) for difficult airways
 
Failed intubation
There were no failed intubations in the easy airway group. There were 18 (11%) in the difficult airway group (Table 5). Fewest failures occurred when using the standard Macintosh, the Lite-Blade and the Europa laryngoscopes, but with the small number studied the difference was not statistically significant (P=0.055).

Grade of intubator
Anaesthetists ranged in experience from 1 to 30 yr practising anaesthesia. There was no correlation between time to intubate with the various laryngoscopes and years of anaesthetic experience (data not shown).


    Discussion
 Top
 Abstract
 Introduction
 Material and methods
 Results
 Discussion
 References
 
Conventional decontamination does not remove protein traces from reusable airway equipment adequately.2 67 This has led to fears over the potential spread of prion-related diseases by this equipment. The observation that tonsils removed from patients who went on to develop variant Creutzfeldt–Jakob disease (vCJD) contained prion protein1 prompted the mandatory introduction of single-use equipment for tonsillectomy surgery in January 2001. After this directive, increased surgical morbidity was recorded, leading to the conclusion that the potential risk of transmitting vCJD was outweighed by the actual risk of the use of single-use (surgical) equipment. The Department of Health directive was reversed in December 2001 with a return to the use of reusable surgical equipment.

During the same time, the use of single-use anaesthetic equipment was also mandatory, thereby stopping the use of reinforced laryngeal masks and necessitating the routine use of tracheal tubes and single-use laryngoscopes.8 When the directive on surgical equipment was reversed, restrictions on the reuse of anaesthetic equipment were initially lifted and then re-imposed in March 2002. The subject is controversial and opposing views have been expressed.914 The role of single-use laryngoscopes in future anaesthetic practice remains uncertain.

Equipment such as laryngoscopes can at present be introduced into practice without the stringent testing of performance that new drugs have to undergo. It is possible that equipment with worse performance than existing devices could be marketed. Many types of single-use blades are manufactured, with different designs and materials. There have been several reports of difficulty obtaining a view of the glottis with single-use laryngoscopes,3 12 but this equipment has not been evaluated formally, apart from a randomized study of one single-use laryngoscope in 100 patients.15 There was no difference between the Vital View and the standard Macintosh laryngoscope in the view that was obtained, but the study was of patients who were almost all easy to intubate. The study could not distinguish performance in cases of difficult intubation.

We compared different designs of single-use laryngoscopes in both easy and difficult intubation. The study was not masked and we used an intubation simulator rather than patients. However, masking in studies of direct laryngoscopy is practically impossible. A clinical study comparing several laryngoscopes, requiring multiple laryngoscopy and studying patients with known difficulty in intubation would be difficult and, in our view, unethical. A high fidelity airway simulator overcomes these problems and allows standardized reproducible intubation conditions of varying difficulty. We see no reason why the relative performance of the laryngoscopes on a simulator should not be the same in a clinical study.

Measuring ease of intubation is difficult. The Cormack and Lehane grade is an insensitive measure because different views of the larynx fall within the same grade. Our measures therefore included a more discriminating measure of laryngeal view, the POGO score,5 and other measures of difficulty (time taken and use of a bougie). The study used a difficult intubation setting that allowed intubation by most anaesthetists to be possible with difficulty when standard equipment was used. This made failed intubation with other laryngoscopes unlikely unless they performed very badly.

The best laryngoscopes were the reusable Macintosh and the Europa. The Europa laryngoscope has a metal blade, which, though slightly less robust than the reusable one, is otherwise almost indistinguishable from it. The best laryngoscope with a plastic blade was the Lite-Blade. The other plastic-bladed laryngoscopes and the reusable blade with a sheath were less adequate.

We believe our results are clinically important. Some of the single-use laryngoscopes tested were significantly worse than conventional equipment. If these results were the same in clinical practice, there would be more difficulty during intubation and more failed intubations. Considerable effort is made routinely to achieve the best conditions for intubation and avoid unnecessary difficulty. A difficult view of the larynx is associated with increased morbidity.16 We believe that intubation equipment that fails to match standard equipment should be avoided and is clinically unsafe. The unregulated use of single-use laryngoscopes must be questioned.


    References
 Top
 Abstract
 Introduction
 Material and methods
 Results
 Discussion
 References
 
1 Hill AF, Butterworth RJ, Joiner S, et al. Investigation of variant Creutzfeldt–Jakob disease and other human prion diseases with tonsil biopsy samples. Lancet 1999; 353: 183–9[CrossRef][ISI][Medline]

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13 Smith G. R Coll Anaesth Bull 2002; No. 12: 599–60

14 Lowe PR, Engelhardt T. Prion-related diseases and anaesthesia. Anaesthesia 2001; 56: 485

15 Asai T, Urchiyama Y, Yamamoto K, Johmura S, Shingu K. Evaluation of the disposable Vital View laryngoscope apparatus. Anaesthesia 2001; 56: 342–5[CrossRef][ISI][Medline]

16 Rose K, Cohen MM. The airway: problems and predictions in 18,500 patients. Can J Anaesth 1994; 41: 372–83[Abstract]