Anaesthesia, 2007, 62, pages 1056–1060 doi:10.1111/j.1365-2044.2007.05178.x .....................................................................................................................................................................................................................
APPARATUS
User satisfaction and forces generated during laryngoscopy using disposable Miller blades: a manikin study* G. Sudhir,1 A. R. Wilkes,2 P. Clyburn,1 I. Aguilera1 and J. E. Hall3 1 Consultant Anaesthetist, Department of Anaesthetics, University Hospital of Wales, Heath Park, Cardiff CF14 4XN, UK 2 Senior Research Fellow, Department of Anaesthetics, 3 Reader & Consultant Anaesthetist, Department of Anaesthetics and Intensive Care Medicine, Wales College of Medicine, Cardiff University, Heath Park, Cardiff CF14 4XN, UK Summary
Increasing awareness of prion-related diseases has led to an increase in the number of disposable laryngoscope blades available. We compared 11 disposable and standard re-usable Miller size 1 blades. In this manikin-based study, we studied user satisfaction for field of view at laryngoscopy, build quality and users’ willingness to use the blade in an emergency situation. These were found to be better with metal disposable blades (p £ 0.001). Vertical and horizontal forces developed during laryngoscopy were greater with plastic than with metal blades. . ......................................................................................................
Correspondence to: Dr G. Sudhir E-mail:
[email protected]
*This study was part presented at the European Society of Anaesthetists 2005 meeting in Vienna. Accepted: 22 May 2007
Disposable laryngoscope blades are increasingly being used due to concerns about cross-infection risk, especially from prion-related diseases such as variant Creutzfeldt-Jakob disease (vCJD). Adult as well as paediatric disposable laryngoscope blades are available constructed from metal or plastic. The light source can be a blademounted bulb, or a light conducting bundle. It is known that the performances of these laryngoscope blades vary. Re-usable blades can be sterilised by using autoclaving or chemical methods. A national survey in 1999 by Esler and colleagues on techniques of decontamination and sterilisation of laryngoscope blades showed a wide variation in practice in the UK [1]. Previous studies have shown that chemical decontamination is effective against bacterial contamination [2, 3]. Although conventional methods of decontamination and sterilisation are effective against bacterial contamination, they are not without associated problems and can result in a decrease in reliability and performance of re-usable laryngoscope blades [4, 5]. Also, conventional methods of sterilisation are not effective against prion particles. Miller and colleagues found the presence of proteinaceous material on supposedly clean and sterilised re-usable laryngoscope 1056
blades [6]. In addition, the time and manpower required for cleaning, decontamination and sterilisation makes it expensive. The use of protective sheaths or condoms is an effective and inexpensive way of preventing crosscontamination [7]; however, they may interfere with the light output from laryngoscope blades. In this context, the use of disposable equipment appears to be a worthwhile alternative to re-usable blades. This has led to the introduction of disposable airway equipment. However, a number of problems have been identified with disposable blades. A French study found that the majority of disposable laryngoscope blades for adult use were inferior to re-usable blades [8]. In a manikin study, Rassam et al. [9] demonstrated that the forces developed during laryngoscopy varied with the use of different disposable Macintosh blades. This study aims to assess user satisfaction with Miller 1 blades, comparing three different aspects: field of view provided by the blade at laryngoscopy, the perceived build quality of the blade and the user’s willingness to use the blade in an emergency situation. We also measured vertical and horizontal forces developed during laryngoscopy and time taken to achieve the best view at laryngoscopy. 2007 The Authors Journal compilation 2007 The Association of Anaesthetists of Great Britain and Ireland
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Anaesthesia, 2007, 62, pages 1056–1060 G. Sudhir et al. Disposable and re-usable Miller blades . ....................................................................................................................................................................................................................
Methods
(a)
Fifty experienced anaesthetists were invited and consented to perform laryngoscopy on a paediatric-intubating manikin in which a grade 1 Cormack and Lehane view was only possible with some difficulty. This was achieved by making the tongue of the manikin bulkier by filling it with cotton wool. The volunteers were briefed about the aim of the study prior to participating in it. Volunteers were informed that a grade 1 Cormack and Lehane view was achievable before they attempted laryngoscopy. Volunteers were asked to perform laryngoscopy with the aim to achieve a grade 1 view of the larynx. They were advised not to do external laryngeal manipulation to improve the view at laryngoscopy. Eleven different disposable blades (Table 1, Figs 1 and 2) and a standard, re-usable, bulb type Miller 1 blade were Table 1 Disposable Miller 1 blades investigated. Name*
Material Light
Vital View Timesco Optima Penlon Crystal Intersurgical Truphatek Liteblade Truphatek Greenlite Timesco Europa Timesco Callisto Proact Metal Max GS90 Proact Metal Max 100 Proact Metal Max 90
Plastic Plastic Plastic Plastic Plastic Metal Metal Metal Metal Metal Metal
Light-conducting bundle Light-conducting bundle Clear plastic light conducting blade Light-conducting bundle Bulb Light-conducting bundle Bulb Light-conducting bundle Light-conducting bundle Bulb Bulb
*Proact and Truphatek blades (Proact Medical Ltd, Great Oakley, Northamptonshire, UK); Timesco blades (Timesco of London, London, UK); Intersurgical (Intersurgical Ltd, Wokingham, Berkshire, UK); Penlon blades (Penlon Limited, Abingdon, UK).
(b)
(c)
(d)
(e)
(f)
Figure 2 Single use metal Miller 1 blades: (a) Timesco Callisto,
(b) Timeso Europa, (c) Truphatek Greenlite, (d) Metal Max GS90, (e) Proact Metal Max 90, (f) Proact Metal Max 100.
compared in this study. The order in which the anaesthetists used the blades for laryngoscopy was randomised using a computer-generated random number technique. The blades were used with their respective handles as recommended by the manufacturer. The handles were numbered rather than named to prevent easy identification by the anaesthetists and avoid possible bias. The blades were replaced after every third use, and the batteries in the laryngoscope handles were checked for any reduction in voltage output at the same time. Batteries were changed if voltage fell below 2.90 V. The vertical force generated during laryngoscopy was measured using an electronic mass balance and the horizontal force was measured with a calibrated force transducer (Fig. 3). The set-up consisted of a paediatric intubating manikin mounted on a board and placed on a
4
(a)
(b)
(c)
(d)
(e)
1
3
2
Figure 1 Single use plastic Miller 1 blades: (a) Penlon Crystal,
(b) Vitalview, (c) Timesco Optima, (d) Intersurgical, (e) Truphatek Lightblade. 2007 The Authors Journal compilation 2007 The Association of Anaesthetists of Great Britain and Ireland
Figure 3 Test set-up: 1 intubating manikin, 2 mass balance,
3 force transducer, 4 laptop computer. 1057
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G. Sudhir et al. Disposable and re-usable Miller blades Anaesthesia, 2007, 62, pages 1056–1060 . ....................................................................................................................................................................................................................
mass balance. The caudal end of the board was placed flush with a calibrated force transducer to measure horizontal forces during laryngoscopy. The mass balance was set to zero prior to the experiment and this then measured vertical forces developed during laryngoscopy. The forces were recorded continuously on a laptop computer with an analogue to digital converter and LABVIEW 7.1 software (National Instruments, Austin, TX). The peak horizontal and vertical forces were recorded and analysed. The time taken for laryngoscopy was measured using a digital stop watch which was started when the laryngoscope was handed to the anaesthetist. The anaesthetist was asked to indicate by saying ‘yes’ when they achieved the best possible view with each blade. This was taken as the end point of laryngoscopy, and the time taken was recorded. Following each laryngoscopy, the anaesthetist was asked to complete a user satisfaction questionnaire. Anaesthetists scored each blade on a 100-mm visual analogue scale, their perceived ‘field of view provided at laryngoscopy’, ‘build quality of the blade’ and ‘their willingness to use that blade in an emergency situation’. Data were collected and entered into an EXCELTM spreadsheet and analysed using SPSS 11.0TM software (SPSS Inc. Chicago, IL). Repeated measures analysis of variance (ANOVA) was used to analyse the data from the visual analogue scores (ease of use, illumination, view and overall clinical satisfaction), and measurements of force and duration. The primary outcome measure was the VAS for field of view as this was considered to be the most important parameter when assessing the suitability of the laryngoscope blade. A p value of < 0.05 was considered to indicate a significant effect.
Table 2 Blades in order of decreasing VAS score for field of
view at laryngoscopy. Results expressed as median (IQR). Blade
FOV
BQ
Timesco Europa Timesco Callisto Proact Metal Max 100 Proact Metal Max 90 Truphatek Greenlite Re-usable Proact Metal Max GS90 Timesco Optima* Penlon Crystal* Intersurgical* Vitalview* Truphatek Liteblade*
83 82 79 78 77 76 70 62 57 50 49 46
81 81 81 80 75 81 74 44 43 36 27 36
(3) (4) (3) (3) (4) (4) (5) (6) (7) (7) (7) (7)
ES (3) (3) (3) (3) (4) (3) (4) (6) (6) (6) (6) (5)
76 74 75 72 65 71 61 39 36 32 28 30
(4) (5) (4) (4) (5) (4) (6) (6) (6) (6) (6) (6)
FOV, field of view at laryngoscopy (Friedman p < 0.0001); BQ, perceived build quality of the blade (Friedman p < 0.0001); ES, user’s willingness to use the blade in an emergency situation (Friedman p < 0.0001). *Plastic blades.
Table 3 Forces developed during laryngoscopy. Blades in order
of increasing vertical force developed during laryngoscopy. Force is in Newtons expressed as mean force (95% CI).
Blade
Vertical force (N)
Horizontal force (N)
Proact Metal Max 100 Proact Metal Max 90 Timesco Europa Re-usable Truphatek Greenlite Timesco Callisto Proact Metal Max GS90 Timesco Optima* Penlon Crystal* Intersurgical* Vitalview* Truphatek Liteblade*
12.66 12.84 13.02 13.27 13.72 13.77 14.85 15.15 15.26 16.53 17.11 18.14
16.64 17.72 17.12 17.75 16.87 16.03 17.89 19.62 20.63 20.83 20.80 20.09
(3.48) (3.25) (3.19) (3.49) (3.65) (3.53) (3.58) (3.63) (3.84) (3.64) (3.58) (3.96)
(2.87) (3.15) (2.64) (3.27) (3.02) (2.88) (3.06) (2.88) (3.90) (3.94) (3.98) (3.50)
*Plastic blades.
Results
The 50 anaesthetists who volunteered for the study included 26 consultants, 23 specialist registrars and 1 associate specialist. All anaesthetists were experienced in anaesthetising children > 2 years of age. The visual analogue scores for field of view, perceived build quality and anaesthetists’ willingness to use the blade in an emergency situation are shown in Table 2. The vertical and horizontal forces developed during laryngoscopy are shown in Table 3. Greater force was generated during laryngoscopy with plastic disposable Miller 1 blades than with the metal disposable and standard re-usable blades. The time taken to achieve the best view at laryngoscopy is shown in Table 4. 1058
Discussion
Metal disposable Miller 1 blades were found to provide better user satisfaction for field of view compared to the plastic blades. The field of view at laryngoscopy could be affected by several factors such as technique of handling the laryngoscope, the intensity and dispersion of light produced by the laryngoscope. An individual anaesthetist’s laryngoscope handling should not have affected the comparison of blades in our study as each anaesthetist performed laryngoscopy with all the laryngoscope blades investigated. The intensity and dispersion of light would differ depending on whether it was a bulb or lightconducting bundle type blade. Also the distraction of the blade due to the forces generated could affect the throw 2007 The Authors Journal compilation 2007 The Association of Anaesthetists of Great Britain and Ireland
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Anaesthesia, 2007, 62, pages 1056–1060 G. Sudhir et al. Disposable and re-usable Miller blades . ....................................................................................................................................................................................................................
Table 4 Time taken for best view at laryngoscopy. Blades are in
the order of increasing time taken for best view. Time is in seconds expressed as mean (standard deviation). Friedman p < 0.0001. Blade
Time; s (SD)
Proact Metal Max 90 Proact Metal Max GS90 Timeso Europa Timesco Callisto Proact Metal Max 100 Truphatek Greenlite Re-usable Timesco Optima* Vital View* Intersurgical* Penlon Crystal* Truphatek Liteblade*
4 4 4 4 5 5 5 5 5 6 6 7
(2) (1) (2) (1) (1) (1) (2) (2) (3) (4) (2) (5)
*Plastic blades.
of light during laryngoscopy and distraction was probably higher with plastic compared to metal blades. In our experiment, we looked at the field of view at laryngoscopy rather than measurement of light output from individual blades as this resembles clinical practice closely. Scholz and colleagues looked at optimum level of illumination at laryngoscopy preferred by anaesthetists and concluded that a brighter illumination may not necessarily be better [10]. The volunteers generally felt that the build quality of metal blades was superior to plastic disposable Miller 1 blades and they preferred to use metal over plastic disposable blades in an emergency situation. Although we numbered the laryngoscope handles instead of naming them to avoid possible bias, the anaesthetists could not be completely blinded to the manufacturers’ labelling on the blades as masking this was difficult. This may have been a source of bias. The vertical as well as horizontal forces developed during laryngoscopy were greater with plastic blades than with metal blades. An increase in force would mean an increase in pressure on the soft tissues. This would suggest that there is greater chance for trauma to the soft tissues with plastic disposable blades together with a possible greater stress response to laryngoscopy. On several occasions, the volunteers felt that they were using more force when using plastic disposable blades compared to their metal counterparts to achieve similar laryngoscopic views. Part of the force generated may be wasted in distraction of the blade, rather than compression and displacement of tissues during laryngoscopy. A recently published paper demonstrated that plastic blades flexed to a greater extent than metal blades when distracting forces were applied [11]. In our 2007 The Authors Journal compilation 2007 The Association of Anaesthetists of Great Britain and Ireland
experiment, we measured actual forces transmitted to the manikin during laryngoscopy, which does not include any force which might have been wasted on distraction of the blade. In spite of this, plastic blades exerted greater force during laryngoscopy compared to metal blades. The reason for this is not clear. Although all blades were marketed as Miller 1 blades, their size and shape were not identical (Figs 1 and 2). This may have contributed to the difference in forces generated during laryngoscopy. The time taken to achieve the best view at laryngoscopy was significantly longer with plastic disposable blades than with metal disposable blades. Although this was statistically significant, the difference in time between the best performing blade and the worst performing blade was only 3 s, which does not appear clinically significant. In our study, a grade 1 view of the vocal cords was achievable with some difficulty. Gauze was inserted into the tongue of the manikin to make laryngoscopy difficult to reveal the differences in the performance of these blades. Had we made laryngoscopy even more difficult, the results might have been different. Although anaesthetists preferred the metal blades to the plastic disposable blades, plastic blades are easy to dispose of after use as they can be incinerated easily, whereas metal blades can not. This is a logistical problem, but considering that metal disposable blades provided significantly better user satisfaction and took less time and less force was exerted during their use to achieve similar laryngoscopy grades, we believe that anaesthetists should be provided with metal disposable blades until plastic disposable blades are made that can perform comparably to those made of metal. Further to their finding of lymphoid tissue contamination on used laryngoscope blades, Hirsch et al. [12] recommended the use of disposable laryngoscope blades whenever possible to prevent possible transmission of prion disease. Our study has shown that the performances of disposable laryngoscope blades may vary greatly. It is also worth noting that although all these disposable blades are marketed as Miller 1 blades, there are differences between these blades in size as well as shape (Figs 1 and 2). We recommend that all disposable laryngoscope blades should be evaluated before introduction into clinical use. Acknowledgements
We would like to thank all the volunteers that participated in the study. All volunteers were experienced practicing anaesthetists employed by the University Hospital of Wales, Cardiff, at the time of the study. We also like to thank the Royal College of Anaesthetists for financial support for the study. 1059
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7 Chen YH, Wong KL, Shieh JP, et al. Use of condoms as blade covers during laryngoscopy, a method to reduce possible cross infection among patients. Infection 2006; 52: 118–23. 8 Fourneret-Vivier A, Rousseau A, Shum J, et al. Single-use laryngoscope blade assessment. Annales Francaises d’Anesthesie et de Reanimation 2004; 23: 694–9. 9 Rassam S, Wilkes AR, Hall JE, Mecklenburgh JS. A comparison of 20 laryngoscope blades using an intubating manikin: visual analogue scores and forces exerted during laryngoscopy. Anaesthesia 2005; 60: 384–94. 10 Scholz A, Farnum N, Wilkes AR, Hampson MA, Hall JE. Minimum and optimum light output of Macintosh size 3 laryngoscopy blades: a manikin study. Anaesthesia 2007; 62: 163–8. 11 Goodwin N, Wilkes AR, Hall JE. Flexibility and light emission of disposable paediatric Miller 1 laryngoscope blades. Anaesthesia 2006; 61: 792–9. 12 Hirsch N, Beckett A, Collinge J, et al. Lymphocyte contamination of laryngoscope blades – a possible vector for transmission of variant Creutzfeldt-Jakob disease. Anaesthesia 2005; 60: 664–7.
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