Anaesthesia 2014, 69, 1331–1336
doi:10.1111/anae.12790
Original Article Effects of laryngoscope handle light source on the light intensity from disposable laryngoscope blades A. D. Milne,1 P. A. Brousseau2 and C. A. Brousseau3 1 Assistant Professor/Staff Anesthesiologist, Department of Anesthesia, Pain Management and Perioperative Medicine, and School of Biomedical Engineering, 3 Respiratory Therapy Student, School of Health Sciences, Dalhousie University, Halifax, Canada 2 Quality Control Officer, Department of Anesthesia, QEII Health Centre, Halifax, Canada
Summary A bench-top study was performed to assess the effects of different laryngoscope handles on the light intensity delivered from disposable metal or plastic laryngoscope blades. The light intensity from both the handle light sources themselves and the combined handle and laryngoscope blade sets was measured using a custom-designed testing system and light meter. Five samples of each disposable blade type were tested and compared with a standard re-usable stainless steel blade using three different handle/light sources (Vital Signs LED, Heine 2.5 V Xenon and 3.5 V Xenon). The light intensity delivered by the disposable blades ranged from 790 to 3846 lux for the different handle types. Overall, the 3.5 V Heine handle delivered the highest light output (p < 0.007) in comparison with the other handles. For the disposable blades, the overall light output was significantly higher from the plastic than the metal blades (p < 0.001).
.................................................................................................................................................................
Correspondence to: A. D. Milne Email: [email protected] Presented in part at the Canadian Anesthesiologists’ Society Annual Meeting, Montreal, Canada, June 2010. Accepted: 1 June 2014
Introduction Single-use or disposable laryngoscope blades are increasingly used for tracheal intubation because of concerns over infection transmission and convenience of reprocessing [1–3]. Multiple brands of disposable metal or plastic blades are now available for use as an alternative to standard re-usable laryngoscope blades. These disposable blades can be used with disposable handles or with standard re-usable handle light sources. In addition to possible infection risk, re-usable blades have been shown to be susceptible to damage from repeated use and sterilisations, necessitating routine quality control testing and periodic replacement. Repeated disinfection © 2014 The Association of Anaesthetists of Great Britain and Ireland
of these re-usable blades has been shown to degrade light intensity by 34–50%, further strengthening the argument for single-use equipment [4, 5]. Previous research has been conducted on metal and plastic disposable laryngoscope blades in terms of their light output [6–9], structural strength [8], forces exerted during manikin intubation [10, 11] and overall clinical performance [12–19], including simulated difficult airway situations [20, 21]. In addition, there have been several case reports of disposable blade breakage during intubation [11, 22, 23]. Clinical studies have reported conflicting results when comparing laryngoscopy between re-usable and 1331
Anaesthesia 2014, 69, 1331–1336
Milne et al. | Effects of laryngoscope handle on light intensity from disposable blades
disposable blades. Three studies have reported equivalent results between metal re-usable blades and plastic disposable blades [12, 17, 18], whereas five studies have reported superior clinical performance of metal re-usable blades over plastic disposable blades [13, 15, 16, 18, 19]. Comparisons of disposable and re-usable metal blades also have reported conflicting results. One study reported similar clinical performance between the two types [15], whereas another study reported superior performance of disposable metal blades over re-usable metal blades that had been used multiple times [14]. Several articles have proposed minimum or optimum laryngoscope light intensity requirements for intubation. There are a wide range of reported values cited in the literature: 200–1938 lux [24]; 597 lux [25]; 700 lux [26]; 867 lux [7]; or 100 cd.m 2 [27]. One manikin-based study employed three different light levels; high (600 lux), medium (200 lux) and low (50 lux), and found no significant differences in the time to intubation for different light levels [28]. The initial draft of the lighting standard from the International Organization for Standardization (ISO) had proposed a minimum of 700 lux [8, 24, 26], but the final published recommendation for minimum light intensity was 500 lux [29]. Subsequent to the release of this standard, a study on paediatric disposable blades demonstrated that only two out of 18 blades met the minimum lighting criteria [30]. However, compliance with this new minimum ISO light level of 500 lux has not been fully evaluated in the adult anaesthesia literature, and limited work has examined the effects of different light handle sources
on the light intensity from ‘fibreoptic type’ disposable adult laryngoscope blades. The purpose of this study was to assess the light intensity delivered from three different re-usable laryngoscope handles and nine different models of disposable adult plastic and metal laryngoscope blades in comparison with a standard re-usable metal blade.
Methods Our institutional research ethics board deemed approval unnecessary for this bench-top qualitycontrol study. Five new disposable adult blade samples (Macintosh size 3) of each type were acquired for testing (see Table 1 for list of models tested). One new re-usable Heineâ Classic stainless steel Macintosh size3 blade was tested as a reference ‘gold standard’. Each blade was tested using three different ‘green’ standard handles [29]. The specific brands tested were a 3.5 V Heine handle with a Xenon bulb and rechargeable nickel metal hydride battery (Herrsching, Germany), a 2.5 V Heine handle with a Xenon bulb and two C cell alkaline batteries, and a Vital Signs Green Light IITM handle (Vital Signs Inc, Totowa, NJ, USA) with a LED light source and two AA alkaline batteries. Light intensity or illuminance (lux), was measured using a previously described custom-built testing chamber [7, 31] and Tenmaâ digital light meter (manufacturer’s accuracy 5%, MCM electronics, Centreville, OH, USA). The enclosed light testing chamber has an interchangeable top cover that can accommodate light testing directly from the handle source alone or from the blade tip in the combined handle and blade setting (Fig. 1).
Table 1 Disposable fibreoptic blade manufacturers and blade material. Key P1 P2 P3 P4 M1 M2 M3 M4 M5
1332
Blade model TM
Crystal Plastic Venticare GE – 4003GSP Heineâ XP Bomimed Callistoâ Crystal MetalTM Steeliteâ Green Rusch LiteTM
Manufacturer/supplier
Type
Penlon Ltd, Abingdon, UK Flexicareâ Medical Ltd, Mountain Ash, UK Vital SignsTM Inc, Totowa, NJ, USA Heine, Herrsching, Germany Bomimed, Winnipeg, MB, Canada Timesco of London Ltd, Basildon, Essex, UK Penlon Ltd, Abingdon, UK Vital Signs Inc, Totowa, NJ, USA Teleflex Medical, Research Triangle Park, NC, USA
Plastic Plastic Plastic Plastic Metal Metal Metal Metal Metal
© 2014 The Association of Anaesthetists of Great Britain and Ireland
Milne et al. | Effects of laryngoscope handle on light intensity from disposable blades
Light intensity delivered directly from each handle light source (Fig. 1a) was measured once before testing the various combinations of handles and blades (Fig. 1b). Each handle and blade combination was then serially tested five times with a 30-s activated period and 60-s rest period between tests. The mean value of the five repeated tests was recorded for each blade and handle configuration. The rechargeable 3.5 V battery/handle set was placed on a recharging unit between tests, and the alkaline batteries were checked with a standard volt meter (Model DM-510; Greenleeâ, Southaven, MS, USA) and frequently replaced to avoid the effects of battery depletion on light intensity [31, 32]. The light output from each handle was also double-checked between testing each batch of blades to ensure that the light intensity delivered to each group of blades was consistent. All testing and measurement was performed by a single author (CB). The
(a)
(b)
Figure 1 Light intensity testing system showing enclosed chambers designed to accommodate testing of light emitted from either (a) the handle alone or (b) the blade tip in the combined handle and blade setting. © 2014 The Association of Anaesthetists of Great Britain and Ireland
Anaesthesia 2014, 69, 1331–1336
order of testing for the nine different blade groups was not formally randomised. The five blade samples within a given group of blades were consecutively tested. Statistical analysis was performed using SPSS 14.0 (SPSS Inc., Chicago, IL, USA). Data were analysed using ANOVA and Tukey’s test. The level of significance was set at p < 0.05.
Results The light intensities measured directly from the three different handles alone were 18700 lux for the Heine 3.5 V handle; 11400 lux for the Heine 2.5 V handle; 8400 lux for the Vital Signs Greenlight II LED handle. When tested in conjunction with a new stainless steel (Heine classic) re-usable blade, the mean (SD) illuminance from these three handles and blade sets were 7538 (322) lux for the Heine 3.5 V, 5600 (199) lux for the Heine 2.5 V and 2372 (187) lux for the Vital Signs Greenlight II. Significant variability was observed in the light intensity delivered from the various disposable blades when tested using the three different handles (Fig. 2). Overall, the new stainless steel re-usable blade delivered significantly more light intensity than the disposable blades (p < 0.001) and the 3.5 V Heine handle battery delivered significantly more light intensity than the other handle types (p < 0.007). The plastic disposable blades delivered significantly more light than the metal disposable blades (p < 0.001). The Penlon Crystal was the brightest of the disposable plastic blades, and the Bomimed metal was the brightest in the disposable metal group (using a 3.5 V handle). With the disposable blades, loss in light transmission was commonly seen at the handle/blade interface or along the length of the blade in some designs (Fig. 3). One disposable metal blade (Bomimed) was noted to have a fragment break loose from its plastic base attachment near the hinge slot when removing the blade from the handle at the end of testing.
Discussion All of the disposable blades tested in our study met the minimum ISO standard of 500 lux [29] when paired with any of the three handles we tested. However, three of the disposable metal blades were in 1333
Anaesthesia 2014, 69, 1331–1336
Milne et al. | Effects of laryngoscope handle on light intensity from disposable blades
Figure 2 Mean light intensity from disposable laryngoscope blades by blade type and handle/light source. The types of blades tested were as follows: P1 – Penlon Crystal (plastic), P2 – Venticaire, P3 – GE 4003GSP, P4 – Heine XP, M1 – Bomimed, M2 – Timesco Callisto, M3 – Penlon Crystal (metal), M4 – Vital Signs Steelite, M5 – Green Rusch Lite. The grey shaded bars represent plastic blades and the white bars represent metal blades. Error bars = SD. The dotted horizontal reference line at 500 lux represents the minimum light intensity as per the ISO standard. the range of 790–890 lux, nearing the minimum preferred level of 700–900 lux as proposed by some authors [7, 26], depending on which handle light source was used. As a group, the disposable plastic blades provided better light output than the disposable metal blades. This finding is interesting in that many clinicians instinctively choose a disposable metal blade over a plastic blade for concerns over structural integrity. Bench-top testing of paediatric laryngoscope blades has demonstrated that metal blades are up to seven times stiffer than plastic blades [8], and our study suggests that clinicians may be sacrificing better lighting conditions for a presumed clinical advantage of mechanical strength when selecting metal disposable blades.
Although several studies have examined the light intensity for different blades, we sought to evaluate the effects of different handle light sources, particularly in the setting of disposable blades paired with re-usable handles. The majority of the prior literature has typically focused on only a single handle light source for a given blade type. Pairing of disposable blades with re-usable handles may be clinically relevant in high-risk cases where re-usable blades may be contraindicated due to risk of cross-infection. The findings from different studies of light intensity with various blades cannot always be directly compared, as there have been many differing methodologies employed for measuring light output.
Figure 3 Comparison of loss in light transmission with different blade designs. Note in the image on the left the amount of projected light lost at the top of the blade or at the connection to the handle. 1334
© 2014 The Association of Anaesthetists of Great Britain and Ireland
Milne et al. | Effects of laryngoscope handle on light intensity from disposable blades
Our reproducible testing method allows for direct comparison of a wide assortment of disposable blade and handle types. The new re-usable stainless steel blade provided higher illuminance values than all of the metal and plastic disposable blades; however, use of a brand new re-usable blade was an artificial ‘best case’ scenario. In the clinical setting, re-usable blades are subjected to multiple usages and cleaning cycles that significantly degrade light output [4, 5]. The performance of reusable devices is dependent on local routine institutional quality control measures to check their light output and eliminate any devices that provide substandard lighting. This is illustrated in one prior study comparing disposable and re-usable metal blades [14], where a common reason for failure with re-usable blades with was cited as poor lighting emitted from older re-usable blades that were likely to be near the end of their useful service lives. A previous quality control audit in our anaesthesia department demonstrated that our combination of re-usable Heine stainless metal blades (with approximately 3–5 years use) and 3.5 V rechargeable handles only produces 5514 (728) lux after routine clinical usage in the operating room [31], which is approximately 25% lower than the light produced by a new blade in this study (7538 (322) lux), but still higher than the majority of disposable blades tested. Despite their ‘green’ standard designation, the quality of blade fit to the handles varied considerably for the different manufacturers, and appreciable loss in light transmission was common at the handle–blade interface. Additional light transmission losses from the light conduction channels along the length of the blade were also seen in some disposable blade designs (Fig. 3). Variability in fit between handles and blades may explain some of the differences in light emission for the nine blade types tested across the three handle combinations. There are some limitations to the present study. While we have shown differences in illuminance delivered by multiple blade and handle combinations in a reproducible bench-top model, we have not demonstrated differences in clinical performance as a function of blade construction type, illuminance level, light spectrum or mechanical strength. These were beyond the scope of this bench-top study. © 2014 The Association of Anaesthetists of Great Britain and Ireland
Anaesthesia 2014, 69, 1331–1336
In conclusion, the choice of laryngoscope handle light source can have significant impact on the light intensity delivered by disposable laryngoscope blades. All of the disposable blades produced less illuminance than a new re-usable stainless steel Heine blade, and overall as a group, the disposable plastic blades provided better illuminance than the disposable metal blades.
Acknowledgement The authors thank Colleen O’Connell, PhD, Research Associate, Perinatal Epidemiology Research Unit, IWK Health Centre for her assistance with the statistical analysis of this project.
Competing interests No external funding and no competing interests declared.
References 1. Call TR, Auerbach FJ, Riddell SW, et al. Nosocomial contamination of laryngoscope handles: challenging current guidelines. Anesthesia and Analgesia 2009; 109: 479–83. 2. Machan MD. Infection control practices of laryngoscope blades: a review of the literature. American Association of Nurse Anesthetists Journal 2012; 80: 274–8. 3. Miller DM, Youkhana I, Karunaratne WU, Pearce A. Presence of protein deposits on ‘cleaned’ re-usable anaesthetic equipment. Anaesthesia 2001; 56: 1069–72. 4. Bucx MJ, De Gast HM, Veldhuis J, Hassing LH, Meulemans A, Kammeyer A. The effect of mechanical cleaning and thermal disinfection on light intensity provided by fibrelight Macintosh laryngoscopes. Anaesthesia 2003; 58: 461–5. 5. Nishiyama T. Changes in the light intensity of the fiberoptic laryngoscope blade by steam sterilization. Anesthesia and Analgesia 2007; 104: 908–10. 6. Anderson KJ, Bhandal N. The effect of single use laryngoscopy equipment on illumination for tracheal intubation. Anaesthesia 2002; 57: 773–7. 7. Cheung KW, Kovacs G, Law JA, Brousseau P, Hill W. Illumination of bulb-on-blade laryngoscopes in the out-of-hospital setting. Academic Emergency Medicine 2007; 14: 496–9. 8. Goodwin N, Wilkes AR, Hall JE. Flexibility and light emission of disposable paediatric Miller 1 laryngoscope blades. Anaesthesia 2006; 61: 792–9. 9. Tousignant G, Tessler MJ. Light intensity and area of illumination provided by various laryngoscope blades. Canadian Journal of Anesthesia 1994; 41: 865–9. 10. 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. 11. Evans A, Vaughan RS, Hall JE, Mecklenburgh J, Wilkes AR. A comparison of the forces exerted during laryngoscopy using disposable and non-disposable laryngoscope blades. Anaesthesia 2003; 58: 869–73. 1335
Anaesthesia 2014, 69, 1331–1336
Milne et al. | Effects of laryngoscope handle on light intensity from disposable blades
12. Asai T, Uchiyama Y, Yamamoto K, Johmura S, Shingu K. Evaluation of the disposable Vital View laryngoscope. Anaesthesia 2001; 56: 342–5. 13. Amour J, Marmion F, Birenbaum A, et al. Comparison of plastic single-use and metal reusable laryngoscope blades for orotracheal intubation during rapid sequence induction of anesthesia. Anesthesiology 2006; 104: 60–4. 14. Amour J, Le Manach YL, Borel M, et al. Comparison of singleuse and reusable metal laryngoscope blades for orotracheal intubation during rapid sequence induction of anesthesia: a multicenter cluster randomized study. Anesthesiology 2010; 112: 325–32. on C, Parienti J-J, Lesage A, et al. Comparison of plastic 15. Bule and metallic single-use and metallic reusable laryngoscope blades: a randomised controlled trial. European Journal of Anaesthesiology 2013; 30: 163–9. 16. Dos Santos FD, Schnakofsky R, Cascio A, Liu J, Merlin MA. Disposable stainless steel vs plastic laryngoscope blades among paramedics. American Journal of Emergency Medicine 2011; 29: 590–3. 17. Galinski M, Adnet F, Tran D, et al. Disposable laryngoscope blades do not interfere with ease of intubation in scheduled general anaesthesia patients. European Journal of Anaesthesiology 2003; 20: 731–5. 18. Galinski M, Catineau J, Rayeh F, et al. Laryngoscope plastic blades in scheduled general anesthesia patients: a comparative randomized study. Journal of Clinical Anesthesia 2011; 23: 107–12. 19. Jabre P, Leroux B, Brohon S, et al. A comparison of plastic single-use with metallic reusable laryngoscope blades for out-ofhospital tracheal intubation. Annals of Emergency Medicine 2007; 50: 258–63. 20. Anderson K, Gambhir S, Glavin R, Kinsella J. The use of an anaesthetic simulator to assess single-use laryngoscopy equipment. International Journal for Quality in Health Care 2006; 18: 17–22.
1336
21. Twigg SJ, McCormick B, Cook TM. Randomized evaluation of the performance of single-use laryngoscopes in simulated easy and difficult intubation. British Journal of Anaesthesia 2003; 90: 8–13. 22. Babb M, Mann S. Disposable laryngoscope blades. Anaesthesia 2002; 57: 286–7. 23. Jefferson P, Perkins V, Edwards VA, Ball DR. Problems with disposable laryngoscope blades. Anaesthesia 2003; 58: 385–6. 24. 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. 25. Milne AD, Brousseau P. What is an unacceptable light level for direct laryngoscopy? Canadian Journal of Anesthesia 2009; 56: 711. 26. Baker PA, Raos AS, Thompson JM, Jacobs RJ. Visual acuity during direct laryngoscopy at different illuminance levels. Anesthesia and Analgesia 2013; 116: 343–50. 27. Skilton RW, Parry D, Arthurs GJ, Hiles P. A study of the brightness of laryngoscope light. Anaesthesia 1996; 51: 667–72. 28. Moore S, Dwyer D, Arendts G. Laryngoscope illumination grade does not influence time to successful manikin intubation. Emergency Medicine Australasia 2009; 21: 131–5. 29. International Organization for Standardization. Anaesthetic and respiratory equipment – laryngoscopes for tracheal intubation. Geneva, Switzerland: ISO 7376, 2009. 30. Baker PA, McQuoid S, Thompson JM, Jacobs RJ. An audit of laryngoscopes and application of a new ISO standard. Pediatric Anesthesia 2011; 21: 428–34. 31. Milne AD, Brousseau CA. Effects of battery type and age on performance of rechargeable laryngoscopes. Journal of Anesthesia 2013; 27: 781–4. 32. Howes BW. The reliability of laryngoscope lights. Anaesthesia 2006; 61: 488–91.
© 2014 The Association of Anaesthetists of Great Britain and Ireland
doi:10.1111/anae.12790
Original Article Effects of laryngoscope handle light source on the light intensity from disposable laryngoscope blades A. D. Milne,1 P. A. Brousseau2 and C. A. Brousseau3 1 Assistant Professor/Staff Anesthesiologist, Department of Anesthesia, Pain Management and Perioperative Medicine, and School of Biomedical Engineering, 3 Respiratory Therapy Student, School of Health Sciences, Dalhousie University, Halifax, Canada 2 Quality Control Officer, Department of Anesthesia, QEII Health Centre, Halifax, Canada
Summary A bench-top study was performed to assess the effects of different laryngoscope handles on the light intensity delivered from disposable metal or plastic laryngoscope blades. The light intensity from both the handle light sources themselves and the combined handle and laryngoscope blade sets was measured using a custom-designed testing system and light meter. Five samples of each disposable blade type were tested and compared with a standard re-usable stainless steel blade using three different handle/light sources (Vital Signs LED, Heine 2.5 V Xenon and 3.5 V Xenon). The light intensity delivered by the disposable blades ranged from 790 to 3846 lux for the different handle types. Overall, the 3.5 V Heine handle delivered the highest light output (p < 0.007) in comparison with the other handles. For the disposable blades, the overall light output was significantly higher from the plastic than the metal blades (p < 0.001).
.................................................................................................................................................................
Correspondence to: A. D. Milne Email: [email protected] Presented in part at the Canadian Anesthesiologists’ Society Annual Meeting, Montreal, Canada, June 2010. Accepted: 1 June 2014
Introduction Single-use or disposable laryngoscope blades are increasingly used for tracheal intubation because of concerns over infection transmission and convenience of reprocessing [1–3]. Multiple brands of disposable metal or plastic blades are now available for use as an alternative to standard re-usable laryngoscope blades. These disposable blades can be used with disposable handles or with standard re-usable handle light sources. In addition to possible infection risk, re-usable blades have been shown to be susceptible to damage from repeated use and sterilisations, necessitating routine quality control testing and periodic replacement. Repeated disinfection © 2014 The Association of Anaesthetists of Great Britain and Ireland
of these re-usable blades has been shown to degrade light intensity by 34–50%, further strengthening the argument for single-use equipment [4, 5]. Previous research has been conducted on metal and plastic disposable laryngoscope blades in terms of their light output [6–9], structural strength [8], forces exerted during manikin intubation [10, 11] and overall clinical performance [12–19], including simulated difficult airway situations [20, 21]. In addition, there have been several case reports of disposable blade breakage during intubation [11, 22, 23]. Clinical studies have reported conflicting results when comparing laryngoscopy between re-usable and 1331
Anaesthesia 2014, 69, 1331–1336
Milne et al. | Effects of laryngoscope handle on light intensity from disposable blades
disposable blades. Three studies have reported equivalent results between metal re-usable blades and plastic disposable blades [12, 17, 18], whereas five studies have reported superior clinical performance of metal re-usable blades over plastic disposable blades [13, 15, 16, 18, 19]. Comparisons of disposable and re-usable metal blades also have reported conflicting results. One study reported similar clinical performance between the two types [15], whereas another study reported superior performance of disposable metal blades over re-usable metal blades that had been used multiple times [14]. Several articles have proposed minimum or optimum laryngoscope light intensity requirements for intubation. There are a wide range of reported values cited in the literature: 200–1938 lux [24]; 597 lux [25]; 700 lux [26]; 867 lux [7]; or 100 cd.m 2 [27]. One manikin-based study employed three different light levels; high (600 lux), medium (200 lux) and low (50 lux), and found no significant differences in the time to intubation for different light levels [28]. The initial draft of the lighting standard from the International Organization for Standardization (ISO) had proposed a minimum of 700 lux [8, 24, 26], but the final published recommendation for minimum light intensity was 500 lux [29]. Subsequent to the release of this standard, a study on paediatric disposable blades demonstrated that only two out of 18 blades met the minimum lighting criteria [30]. However, compliance with this new minimum ISO light level of 500 lux has not been fully evaluated in the adult anaesthesia literature, and limited work has examined the effects of different light handle sources
on the light intensity from ‘fibreoptic type’ disposable adult laryngoscope blades. The purpose of this study was to assess the light intensity delivered from three different re-usable laryngoscope handles and nine different models of disposable adult plastic and metal laryngoscope blades in comparison with a standard re-usable metal blade.
Methods Our institutional research ethics board deemed approval unnecessary for this bench-top qualitycontrol study. Five new disposable adult blade samples (Macintosh size 3) of each type were acquired for testing (see Table 1 for list of models tested). One new re-usable Heineâ Classic stainless steel Macintosh size3 blade was tested as a reference ‘gold standard’. Each blade was tested using three different ‘green’ standard handles [29]. The specific brands tested were a 3.5 V Heine handle with a Xenon bulb and rechargeable nickel metal hydride battery (Herrsching, Germany), a 2.5 V Heine handle with a Xenon bulb and two C cell alkaline batteries, and a Vital Signs Green Light IITM handle (Vital Signs Inc, Totowa, NJ, USA) with a LED light source and two AA alkaline batteries. Light intensity or illuminance (lux), was measured using a previously described custom-built testing chamber [7, 31] and Tenmaâ digital light meter (manufacturer’s accuracy 5%, MCM electronics, Centreville, OH, USA). The enclosed light testing chamber has an interchangeable top cover that can accommodate light testing directly from the handle source alone or from the blade tip in the combined handle and blade setting (Fig. 1).
Table 1 Disposable fibreoptic blade manufacturers and blade material. Key P1 P2 P3 P4 M1 M2 M3 M4 M5
1332
Blade model TM
Crystal Plastic Venticare GE – 4003GSP Heineâ XP Bomimed Callistoâ Crystal MetalTM Steeliteâ Green Rusch LiteTM
Manufacturer/supplier
Type
Penlon Ltd, Abingdon, UK Flexicareâ Medical Ltd, Mountain Ash, UK Vital SignsTM Inc, Totowa, NJ, USA Heine, Herrsching, Germany Bomimed, Winnipeg, MB, Canada Timesco of London Ltd, Basildon, Essex, UK Penlon Ltd, Abingdon, UK Vital Signs Inc, Totowa, NJ, USA Teleflex Medical, Research Triangle Park, NC, USA
Plastic Plastic Plastic Plastic Metal Metal Metal Metal Metal
© 2014 The Association of Anaesthetists of Great Britain and Ireland
Milne et al. | Effects of laryngoscope handle on light intensity from disposable blades
Light intensity delivered directly from each handle light source (Fig. 1a) was measured once before testing the various combinations of handles and blades (Fig. 1b). Each handle and blade combination was then serially tested five times with a 30-s activated period and 60-s rest period between tests. The mean value of the five repeated tests was recorded for each blade and handle configuration. The rechargeable 3.5 V battery/handle set was placed on a recharging unit between tests, and the alkaline batteries were checked with a standard volt meter (Model DM-510; Greenleeâ, Southaven, MS, USA) and frequently replaced to avoid the effects of battery depletion on light intensity [31, 32]. The light output from each handle was also double-checked between testing each batch of blades to ensure that the light intensity delivered to each group of blades was consistent. All testing and measurement was performed by a single author (CB). The
(a)
(b)
Figure 1 Light intensity testing system showing enclosed chambers designed to accommodate testing of light emitted from either (a) the handle alone or (b) the blade tip in the combined handle and blade setting. © 2014 The Association of Anaesthetists of Great Britain and Ireland
Anaesthesia 2014, 69, 1331–1336
order of testing for the nine different blade groups was not formally randomised. The five blade samples within a given group of blades were consecutively tested. Statistical analysis was performed using SPSS 14.0 (SPSS Inc., Chicago, IL, USA). Data were analysed using ANOVA and Tukey’s test. The level of significance was set at p < 0.05.
Results The light intensities measured directly from the three different handles alone were 18700 lux for the Heine 3.5 V handle; 11400 lux for the Heine 2.5 V handle; 8400 lux for the Vital Signs Greenlight II LED handle. When tested in conjunction with a new stainless steel (Heine classic) re-usable blade, the mean (SD) illuminance from these three handles and blade sets were 7538 (322) lux for the Heine 3.5 V, 5600 (199) lux for the Heine 2.5 V and 2372 (187) lux for the Vital Signs Greenlight II. Significant variability was observed in the light intensity delivered from the various disposable blades when tested using the three different handles (Fig. 2). Overall, the new stainless steel re-usable blade delivered significantly more light intensity than the disposable blades (p < 0.001) and the 3.5 V Heine handle battery delivered significantly more light intensity than the other handle types (p < 0.007). The plastic disposable blades delivered significantly more light than the metal disposable blades (p < 0.001). The Penlon Crystal was the brightest of the disposable plastic blades, and the Bomimed metal was the brightest in the disposable metal group (using a 3.5 V handle). With the disposable blades, loss in light transmission was commonly seen at the handle/blade interface or along the length of the blade in some designs (Fig. 3). One disposable metal blade (Bomimed) was noted to have a fragment break loose from its plastic base attachment near the hinge slot when removing the blade from the handle at the end of testing.
Discussion All of the disposable blades tested in our study met the minimum ISO standard of 500 lux [29] when paired with any of the three handles we tested. However, three of the disposable metal blades were in 1333
Anaesthesia 2014, 69, 1331–1336
Milne et al. | Effects of laryngoscope handle on light intensity from disposable blades
Figure 2 Mean light intensity from disposable laryngoscope blades by blade type and handle/light source. The types of blades tested were as follows: P1 – Penlon Crystal (plastic), P2 – Venticaire, P3 – GE 4003GSP, P4 – Heine XP, M1 – Bomimed, M2 – Timesco Callisto, M3 – Penlon Crystal (metal), M4 – Vital Signs Steelite, M5 – Green Rusch Lite. The grey shaded bars represent plastic blades and the white bars represent metal blades. Error bars = SD. The dotted horizontal reference line at 500 lux represents the minimum light intensity as per the ISO standard. the range of 790–890 lux, nearing the minimum preferred level of 700–900 lux as proposed by some authors [7, 26], depending on which handle light source was used. As a group, the disposable plastic blades provided better light output than the disposable metal blades. This finding is interesting in that many clinicians instinctively choose a disposable metal blade over a plastic blade for concerns over structural integrity. Bench-top testing of paediatric laryngoscope blades has demonstrated that metal blades are up to seven times stiffer than plastic blades [8], and our study suggests that clinicians may be sacrificing better lighting conditions for a presumed clinical advantage of mechanical strength when selecting metal disposable blades.
Although several studies have examined the light intensity for different blades, we sought to evaluate the effects of different handle light sources, particularly in the setting of disposable blades paired with re-usable handles. The majority of the prior literature has typically focused on only a single handle light source for a given blade type. Pairing of disposable blades with re-usable handles may be clinically relevant in high-risk cases where re-usable blades may be contraindicated due to risk of cross-infection. The findings from different studies of light intensity with various blades cannot always be directly compared, as there have been many differing methodologies employed for measuring light output.
Figure 3 Comparison of loss in light transmission with different blade designs. Note in the image on the left the amount of projected light lost at the top of the blade or at the connection to the handle. 1334
© 2014 The Association of Anaesthetists of Great Britain and Ireland
Milne et al. | Effects of laryngoscope handle on light intensity from disposable blades
Our reproducible testing method allows for direct comparison of a wide assortment of disposable blade and handle types. The new re-usable stainless steel blade provided higher illuminance values than all of the metal and plastic disposable blades; however, use of a brand new re-usable blade was an artificial ‘best case’ scenario. In the clinical setting, re-usable blades are subjected to multiple usages and cleaning cycles that significantly degrade light output [4, 5]. The performance of reusable devices is dependent on local routine institutional quality control measures to check their light output and eliminate any devices that provide substandard lighting. This is illustrated in one prior study comparing disposable and re-usable metal blades [14], where a common reason for failure with re-usable blades with was cited as poor lighting emitted from older re-usable blades that were likely to be near the end of their useful service lives. A previous quality control audit in our anaesthesia department demonstrated that our combination of re-usable Heine stainless metal blades (with approximately 3–5 years use) and 3.5 V rechargeable handles only produces 5514 (728) lux after routine clinical usage in the operating room [31], which is approximately 25% lower than the light produced by a new blade in this study (7538 (322) lux), but still higher than the majority of disposable blades tested. Despite their ‘green’ standard designation, the quality of blade fit to the handles varied considerably for the different manufacturers, and appreciable loss in light transmission was common at the handle–blade interface. Additional light transmission losses from the light conduction channels along the length of the blade were also seen in some disposable blade designs (Fig. 3). Variability in fit between handles and blades may explain some of the differences in light emission for the nine blade types tested across the three handle combinations. There are some limitations to the present study. While we have shown differences in illuminance delivered by multiple blade and handle combinations in a reproducible bench-top model, we have not demonstrated differences in clinical performance as a function of blade construction type, illuminance level, light spectrum or mechanical strength. These were beyond the scope of this bench-top study. © 2014 The Association of Anaesthetists of Great Britain and Ireland
Anaesthesia 2014, 69, 1331–1336
In conclusion, the choice of laryngoscope handle light source can have significant impact on the light intensity delivered by disposable laryngoscope blades. All of the disposable blades produced less illuminance than a new re-usable stainless steel Heine blade, and overall as a group, the disposable plastic blades provided better illuminance than the disposable metal blades.
Acknowledgement The authors thank Colleen O’Connell, PhD, Research Associate, Perinatal Epidemiology Research Unit, IWK Health Centre for her assistance with the statistical analysis of this project.
Competing interests No external funding and no competing interests declared.
References 1. Call TR, Auerbach FJ, Riddell SW, et al. Nosocomial contamination of laryngoscope handles: challenging current guidelines. Anesthesia and Analgesia 2009; 109: 479–83. 2. Machan MD. Infection control practices of laryngoscope blades: a review of the literature. American Association of Nurse Anesthetists Journal 2012; 80: 274–8. 3. Miller DM, Youkhana I, Karunaratne WU, Pearce A. Presence of protein deposits on ‘cleaned’ re-usable anaesthetic equipment. Anaesthesia 2001; 56: 1069–72. 4. Bucx MJ, De Gast HM, Veldhuis J, Hassing LH, Meulemans A, Kammeyer A. The effect of mechanical cleaning and thermal disinfection on light intensity provided by fibrelight Macintosh laryngoscopes. Anaesthesia 2003; 58: 461–5. 5. Nishiyama T. Changes in the light intensity of the fiberoptic laryngoscope blade by steam sterilization. Anesthesia and Analgesia 2007; 104: 908–10. 6. Anderson KJ, Bhandal N. The effect of single use laryngoscopy equipment on illumination for tracheal intubation. Anaesthesia 2002; 57: 773–7. 7. Cheung KW, Kovacs G, Law JA, Brousseau P, Hill W. Illumination of bulb-on-blade laryngoscopes in the out-of-hospital setting. Academic Emergency Medicine 2007; 14: 496–9. 8. Goodwin N, Wilkes AR, Hall JE. Flexibility and light emission of disposable paediatric Miller 1 laryngoscope blades. Anaesthesia 2006; 61: 792–9. 9. Tousignant G, Tessler MJ. Light intensity and area of illumination provided by various laryngoscope blades. Canadian Journal of Anesthesia 1994; 41: 865–9. 10. 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. 11. Evans A, Vaughan RS, Hall JE, Mecklenburgh J, Wilkes AR. A comparison of the forces exerted during laryngoscopy using disposable and non-disposable laryngoscope blades. Anaesthesia 2003; 58: 869–73. 1335
Anaesthesia 2014, 69, 1331–1336
Milne et al. | Effects of laryngoscope handle on light intensity from disposable blades
12. Asai T, Uchiyama Y, Yamamoto K, Johmura S, Shingu K. Evaluation of the disposable Vital View laryngoscope. Anaesthesia 2001; 56: 342–5. 13. Amour J, Marmion F, Birenbaum A, et al. Comparison of plastic single-use and metal reusable laryngoscope blades for orotracheal intubation during rapid sequence induction of anesthesia. Anesthesiology 2006; 104: 60–4. 14. Amour J, Le Manach YL, Borel M, et al. Comparison of singleuse and reusable metal laryngoscope blades for orotracheal intubation during rapid sequence induction of anesthesia: a multicenter cluster randomized study. Anesthesiology 2010; 112: 325–32. on C, Parienti J-J, Lesage A, et al. Comparison of plastic 15. Bule and metallic single-use and metallic reusable laryngoscope blades: a randomised controlled trial. European Journal of Anaesthesiology 2013; 30: 163–9. 16. Dos Santos FD, Schnakofsky R, Cascio A, Liu J, Merlin MA. Disposable stainless steel vs plastic laryngoscope blades among paramedics. American Journal of Emergency Medicine 2011; 29: 590–3. 17. Galinski M, Adnet F, Tran D, et al. Disposable laryngoscope blades do not interfere with ease of intubation in scheduled general anaesthesia patients. European Journal of Anaesthesiology 2003; 20: 731–5. 18. Galinski M, Catineau J, Rayeh F, et al. Laryngoscope plastic blades in scheduled general anesthesia patients: a comparative randomized study. Journal of Clinical Anesthesia 2011; 23: 107–12. 19. Jabre P, Leroux B, Brohon S, et al. A comparison of plastic single-use with metallic reusable laryngoscope blades for out-ofhospital tracheal intubation. Annals of Emergency Medicine 2007; 50: 258–63. 20. Anderson K, Gambhir S, Glavin R, Kinsella J. The use of an anaesthetic simulator to assess single-use laryngoscopy equipment. International Journal for Quality in Health Care 2006; 18: 17–22.
1336
21. Twigg SJ, McCormick B, Cook TM. Randomized evaluation of the performance of single-use laryngoscopes in simulated easy and difficult intubation. British Journal of Anaesthesia 2003; 90: 8–13. 22. Babb M, Mann S. Disposable laryngoscope blades. Anaesthesia 2002; 57: 286–7. 23. Jefferson P, Perkins V, Edwards VA, Ball DR. Problems with disposable laryngoscope blades. Anaesthesia 2003; 58: 385–6. 24. 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. 25. Milne AD, Brousseau P. What is an unacceptable light level for direct laryngoscopy? Canadian Journal of Anesthesia 2009; 56: 711. 26. Baker PA, Raos AS, Thompson JM, Jacobs RJ. Visual acuity during direct laryngoscopy at different illuminance levels. Anesthesia and Analgesia 2013; 116: 343–50. 27. Skilton RW, Parry D, Arthurs GJ, Hiles P. A study of the brightness of laryngoscope light. Anaesthesia 1996; 51: 667–72. 28. Moore S, Dwyer D, Arendts G. Laryngoscope illumination grade does not influence time to successful manikin intubation. Emergency Medicine Australasia 2009; 21: 131–5. 29. International Organization for Standardization. Anaesthetic and respiratory equipment – laryngoscopes for tracheal intubation. Geneva, Switzerland: ISO 7376, 2009. 30. Baker PA, McQuoid S, Thompson JM, Jacobs RJ. An audit of laryngoscopes and application of a new ISO standard. Pediatric Anesthesia 2011; 21: 428–34. 31. Milne AD, Brousseau CA. Effects of battery type and age on performance of rechargeable laryngoscopes. Journal of Anesthesia 2013; 27: 781–4. 32. Howes BW. The reliability of laryngoscope lights. Anaesthesia 2006; 61: 488–91.
© 2014 The Association of Anaesthetists of Great Britain and Ireland
