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Original Articles – General

A comparison of the Laryngopharyngeal Examination blade and the English Macintosh laryngoscope blade using an intubating manikin: a prospective randomized crossover study

Ashfaque, Muhammada; Mason, Jonathanb; Al-Shaikh, Bahab; Adegoke, Kennetha

Author Information
European Journal of Anaesthesiology: November 2009 - Volume 26 - Issue 11 - p 917-922
doi: 10.1097/EJA.0b013e32832c7848

Abstract

Introduction

Insertion of a nasogastric tube (NGT) is a routine task that anaesthetists carry out in anaesthetized and critically ill patients. Quite often this proves to be difficult due to various anatomical factors. An important factor is the presence of a tracheal tube. Visualization of the hypopharynx with a conventional (Macintosh) laryngoscope blade is difficult as the tracheal tube can be in the way of the anaesthetist's view. Some anaesthetists tend to insert an NGT just before tracheal intubation. This, however, is not practicable in emergency situations, in anaesthetized or critically ill and ventilated patients. NGTs when inserted blindly can lead to application of excessive force. This may result in different complications varying in degree of severity from minor to fatal [1–6]. The National Patient Safety Agency issued an alert in 2005 quoting 11 deaths and one case of nonfatal harm caused by misplaced NGTs and nasoenteral feeding tubes [7]. Different authors have suggested methods to overcome this difficulty with varying degrees of success [8–10]. There is no instrument which, at present, can effectively move the tracheal tube out of the way, to give an unobstructed view of the hypopharynx for inserting or changing a NGT in an intubated patient.

A new laryngoscope blade, Laryngopharyngeal Examination (LpEx) blade, was designed to help overcome this difficulty [11]. At present, anaesthetists most commonly use the English Macintosh blade for laryngoscopy and tracheal intubation extending its use, at times, for NGT insertion. This crossover prospective randomized trial was designed to compare the English Macintosh blade with the LpEx blade in terms of view of the hypopharynx obtained and time to perform NGT insertion. Ease of laryngoscopy and tracheal intubation were also compared.

Methods

With approval from the Local Research Ethics Committee, a total of 81 anaesthetists of different grades working in two hospitals took part in the study. The range of anaesthetic experience was quite wide but, considering the nature of skills needed, it was thought that the task was well within the basic competencies of an anaesthetist and a level of experience of 3 months or more should have been enough for the purposes of this comparative study. Participants were randomly allocated to one or other of groups ‘A’ and ‘B’, using block randomization, with 41 and 40 participants, respectively. Participants in group ‘A’ assessed the LpEx blade first, whereas those in group ‘B’ assessed the English Macintosh blade first.

Following a demonstration on the correct use of the LpEx blade, participants were asked to familiarize themselves with the use of the new instrument by practising on the manikin until they felt comfortable and confident to proceed to assessment. This was done to exclude learning effect as a possible variable in the conduct of the study. Once the demonstration of use and learning attempts on LpEx blade were completed, the participants were allocated the next number on the response sheets. This was done for the comparison of individual responses of participants for either instrument. Participants were given sealed envelopes giving the order of the blade to be assessed first and subsequently and were opened by each participant just prior to assessment.

The assessments were carried out in a room where only the participant assessing the laryngoscope blades and another independent person who facilitated the assessment were present. This independent person was either an operating department practitioner or an anaesthetic nurse familiar with various parts of equipment being used in the assessment. The observing person called the next participant into the room once the previous one had left the room and the responses had been recorded and collated.

The manikin was placed on a surface with the facility of adjustment of the height to suit the participants. The participants recorded their visual analogue scale (VAS) scores for ease of examination of the hypopharynx and the ease of insertion of the NGT after tracheal intubation and also ease of laryngoscopy and tracheal intubation. The VAS scores from 0 to 10 were used, two extremes being from ‘not at all easy’ to ‘very easy’.

The participants were required to complete the assessment for the first blade and then for the second blade according to the allocated sequence. They recorded their VAS scores for each blade separately on anonymous response sheets. The sizes of the tracheal tube (7 mm inner diameter), the blades (FO 4), the manikin (adult size), the NGT (FrG 16) and the Magill's forceps (adult) were the same for all assessments.

The independent observer also recorded the time taken to pass the NGT in the manikin with both the blades using a digital stopwatch. That time was recorded from the moment the participants held the NGT in their hand to the moment it was inserted as indicated by the participants and witnessed by the observer. This was done for the first six participants, but the observers had noticed that the participants were not all proceeding in the same way. It was, therefore, agreed that, after tracheal intubation, the participants would pause for a moment and then would let the observer know they were ready to carry out the NGT insertion. All the remaining participants carried out assessments of laryngoscope blades with a pause after tracheal intubation. This was done to standardize the conduct of and starting time for the manoeuvre.

In cases of equipment failure, the procedure to insert the NGT was restarted and the time reinitialized and the recorded time was the time to the successful insertion of the NGT. In cases in which more than one attempt was made to insert the NGT, only the times taken for completed attempts were recorded and the observer ignored any abortive attempts.

Statistical methods

Our primary endpoints were the ease of examination of the hypopharynx and the ease of NGT insertion after tracheal intubation. The secondary endpoints were the ease of laryngoscopy and tracheal intubation and the time taken for NGT insertion. The primary endpoint used when determining the sample size was the difference in VAS scores for ease of examination of the hypopharynx and the ease of insertion of the NGT after tracheal intubation. The sample size was calculated to achieve a power of more than 80%.

Paired t-tests were used to determine whether there was a difference between the mean VAS scores of each of the laryngoscope blades for ease of examination of the hypopharynx and ease of insertion of the NGT after tracheal intubation. Two-sided alternative hypotheses were used. It was assumed that a VAS score difference of at least 1 was clinically significant. This was a clinical and not a statistical decision. Lower 95% confidence limits were generated for the proportion of participants who awarded equal or greater VAS scores to the LpEx blade for these two actions/functions.

The ratio of the time taken using the LpEx blade to the time taken using the Macintosh blade was approximately normal, so a t-test against a two-sided alternative hypothesis was used to determine whether the mean of this ratio was different from unity. Although the distribution of the difference in VAS scores was not symmetrical as it can take only integer values, the sample means were approximately normally distributed. Therefore, no test for kurtosis was applied. The use of the t-test was considered justified by the Central Limit Theorem. A value of P of 0.05 or less would be considered statistically significant.

Analysis of data was performed using a test for noninferiority of the LpEx blade comparing VAS scores for the ease of laryngoscopy and tracheal intubation between the two laryngoscope blades.

Results

A total of 81 anaesthetists from the two main hospitals in the East Kent Hospitals NHS Trust participated in the study. The anaesthetic experience of the participants ranged between 1 and 30 years except for two trainees, one of whom had worked in anaesthesia for 6 months and the other for only 5 months.

Although the participants were not stratified for any factor, the distribution of participants of various grades and levels of experience were similar in the two groups (Table 1).

Table 1
Table 1:
Distribution of different grades of participants in the groups

Ease of examination of the hypopharynx after tracheal intubation

Data from all participants were used in the comparison of ease of examination of the hypopharynx after tracheal intubation. The VAS scores for this action ranged from 6 to 10 (mean = 8.46 units) and from 3 to 10 (mean = 6.47 units) for LpEx and Macintosh blades, respectively. VAS scores of the first six participants for this action were similar to those of other participants and excluding them from statistical analysis did not substantially change the conclusions drawn for this action. The mean difference (SD) in VAS scores between the two blades (LpEx−Macintosh) for ease of examination of the hypopharynx was found to be 1.99 (1.86). The score for the LpEx blade was greater than that for the Macintosh blade (P < 0.001). It was estimated that at least 92% of anaesthetists would find the LpEx blade similar to or better than the Macintosh blade for this action (lower 95% confidence limit; Table 2) (Fig. 1).

Table 2
Table 2:
Number of participants (%) awarding visual analogue scale scores for ease of examination of hypopharynx after tracheal intubation
Fig. 1
Fig. 1

Ease of nasogastric tube insertion after tracheal intubation

Data from all participants were used to compare ease of NGT insertion after tracheal intubation. Six participants made two or more attempts to insert the NGT after tracheal intubation. The results of the analysis were not affected materially by omitting any of the first six participants or the one participant who failed to complete this task using the Macintosh blade. At least six participants required more than one attempt with one or more of the blades (Fig. 2).

Fig. 2
Fig. 2

The mean VAS scores for this function were 8.43 (range 6–10 VAS units) and 6.37 (range 2–10 VAS units) for the LpEx and Macintosh blades, respectively. The mean difference (SD) between VAS scores for the two blades for this action was 2.06 (2.129). Statistical analysis showed that the mean score for the LpEx blade was significantly greater than the mean score for the Macintosh blade for this action (P < 0.001). At least 87% of anaesthetists found the LpEx blade similar to or better than the Macintosh blade for NGT insertion after tracheal intubation (lower 95% confidence limit; Table 3).

Table 3
Table 3:
Number of participants (%) awarding visual analogue scale scores for ease of insertion of the nasogastric tube after tracheal intubation

Time for nasogastric tube insertion

Data acquired from the first six participants were not used for analysis of the time needed for NGT insertion. Time recording for these participants was done using a different starting point. Another participant who could not insert the NGT with the Macintosh laryngoscope blade was also excluded from analysis of this time ratio. The time taken to complete NGT insertion ranged from 7.12 to 55.13 s and from 7.33 to 101.32 s for the LpEx and Macintosh blades, respectively. The mean (SD) of the ratio ‘time using LpEx/time using Macintosh’ was found to be 0.921 (0.3396), that is, the mean of the ratio was less than 1 (P = 0.05). The average time taken for insertion of the NGT using the LpEx blade was 92.1% of the time taken with the Macintosh blade for the same action (95% confidence interval: 84–100%; Fig. 3).

Fig. 3
Fig. 3

Ease of laryngoscopy and tracheal intubation

Statistical analysis of VAS scores for the ease of laryngoscopy and tracheal intubation included all participants. The VAS scores for this action ranged from 5 to 10 (mean = 8.38 units) and from 4 to 10 (mean = 8.69) for LpEx and Macintosh blades, respectively. The mean difference (SD) between scores for the two blades (LpEx−Macintosh) was −0.31 (0.944), which was greater than the clinically significant mean difference in VAS scores of −1, thus showing noninferiority of the LpEx blade (P < 0.001). A total of 68% of the participants rated the LpEx blade comparable or superior to the Macintosh blade. Of the 32% of participants who awarded the LpEx blade a lower score, only 11% awarded a VAS score that differed by more than one VAS unit (Fig. 4).

Fig. 4
Fig. 4

Discussion

The design of the LpEx blade differs from the English Macintosh blade in that it has a furrow on its lingual aspect designed to accommodate the shaft of an in-situ tracheal tube. The proximal end of the blade has a different configuration and the connection to the battery handle is not in the line of the shaft of the tracheal tube when in use. Visualization of part of the shaft of the tracheal tube along with arytenoid prominences on either side of the posterior commissure of the larynx and the upper end of the oesophagus ensures that the nasogastric tube can be passed into the correct passage, thus avoiding the possible complications of blind insertion.

Most of the descriptions of airway management equipment and randomized controlled trials concentrating upon the airway have centred on laryngoscopy and tracheal intubation [12–18]. To our knowledge, there has been no such trial so far that compared ease of visualization of the hypopharynx and ease of insertion of a NGT after tracheal intubation under direct vision. This prospective and randomized crossover study has compared the ease of examination of the hypopharynx and NGT insertion after tracheal intubation, under direct vision, as well as the ease of laryngoscopy and tracheal intubation in a manikin between the English Macintosh blade and LpEx blade. It is unique in that it involves a device which offers laryngoscopic views equivalent to those obtainable with a Macintosh blade. In addition, after tracheal intubation, the LpEx blade facilitates insertion of a NGT under direct vision by displacing the tracheal tube along with the structures of the floor of the mouth while keeping the tracheal tube in the midline. This feature allows recognition of the posterior aspect of rima glottidis behind the tracheal tube and opens up the upper end of oesophagus, thus facilitating the insertion of a NGT under direct vision.

There were statistically significant differences in mean VAS scores recorded with the LpEx blade compared with the English Macintosh blade for ease of visualization of the hypopharynx and for the ease of insertion of the NGT after tracheal intubation, thus supporting the primary endpoint of the study. The reasons for these highly significant differences could have been the configuration of the LpEx blade with the furrow accommodating the tracheal tube within it and enabling the operator to move it out of the line of vision, thus allowing the upper end of the oesophagus to open up without kinking of the tracheal tube.

The results of this study have also shown significant evidence of noninferiority of the LpEx blade for laryngoscopy and tracheal intubation, thus supporting the secondary endpoint of the study. In fact, 68% of participants found that the laryngeal views obtained with the LpEx blade were as good as those with the English Macintosh blade. If we calculate by correcting for maximum allowable difference in VAS score of one unit, 89% of participants found the LpEx blade comparable or superior to the Macintosh blade for this purpose.

These findings confirm the usefulness of the LpEx blade, despite the potential influence of either a new learning effect or previously acquired techniques.

Various descriptions of methods to facilitate the task of NGT insertion exist in tracheally intubated patients, but there is none that has found universal acceptance. The reason why one technique is not universally adopted is that no single technique is helpful in all situations. An important factor has been the absence of an instrument that could be simple, convenient, easy and ready to use. The LpEx blade can be a useful and practical addition to these techniques. The time taken to carry out the NGT insertion is another important issue in an intubated and ventilated patient. Various methods have been tried. These include use of the reverse Sellick manoeuvre [19], forward displacement of the larynx [20], nasopharyngeal airways [21], use of a guidewire [22] or a second NGT for railroading [23], use of a longitudinally split tracheal tube [24] and requesting patient help and cooperation [25]. Recently, there have been descriptions of the use of a video laryngoscope (GlideScope) for tracheal intubation [26–28]. The time taken for tracheal intubation has been shown to be longer when compared with the Macintosh laryngoscope and to involve costly equipment, offering only indirect views and requiring training of staff to enable them to carry out the procedure correctly.

It has been shown that the most successful way of inserting orogastric tubes and NGTs is the use of some mechanism for avoiding impaction of the tubes in the piriform sinus or against the arytenoid cartilages [29]. The use of lateral neck pressure to compress the piriform sinus and to move arytenoid cartilages medially, thus facilitating passage of the NGT into the oesophagus, has been recommended. This same endpoint if achieved under direct vision would be more desirable and would eradicate the probability of misplacement of NGTs.

At present, there is no such instrument available in an anaesthetist's armamentarium that could promise to facilitate insertion of a NGT in the presence of a tracheal tube in the airway under direct vision. In the absence of such a device, anaesthetists have been tempted to try and use the Macintosh blade to insert the NGTs, despite the potential tissue trauma and the need to juggle with the in-situ tracheal tube in anaesthetized or critically ill and ventilated patients. The LpEx blade can potentially help in NGT insertion in all such cases while still preserving the essentially basic function of visualization of the larynx and help in insertion of the tracheal tube.

We conclude from the results of this study that the LpEx laryngoscope blade can be used to facilitate laryngoscopy and tracheal intubation followed by NGT insertion, in a manikin, as and when required according to clinical need. Further studies in patients will establish the degree of its usefulness in clinical situations.

Acknowledgements

The authors acknowledge the help and support of Mr Mark Beerling and Mr Alan Green of Penlon UK in the development of the prototype of the LpEx blade, the R&D department of East Kent Hospitals NHS Trust for funding this study, Dr Alexa Laurence and the Kent arm of the South East Research and Development Support Unit, Centre for Health Services Studies, University of Kent, Canterbury, in statistical design and analysis and Dr Mark Scott, Innovations Manager, NISE Hub, for his efforts in liaising among all these teams.

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Keywords:

anaesthetic equipment; laryngoscopy; Macintosh blade

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