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An in vitro assessment of light intensity provided during direct laryngeal visualization by videolaryngoscopes with Macintosh geometry blades

Une évaluation in vitro de l’intensité lumineuse fournie lors de la visualisation directe du larynx par les vidéolaryngoscopes munis de lames à géométrie Macintosh

Abstract

Background

Adequate illumination of the larynx is needed during laryngoscopy to facilitate tracheal intubation. The International Organization for Standardization (ISO) has established a minimum light intensity for direct laryngoscopy (DL) of over 500 lux for at least ten minutes, but no such standard exists for Macintosh geometry videolaryngoscope (Mac-VL) blades, which allow for both direct or indirect (videoscopic) viewing of the larynx. Using in situ bench and in vitro testing in a human cadaver, we determined illumination and luminance values delivered by various Mac-VLs and compared these with published minimum lighting benchmarks as well as a reference direct laryngoscope.

Methods

We tested six Mac-VLs (i-view™, McGRATH™ MAC, GlideScope® Spectrum™ [single-use] DVM S4, GlideScope® Titanium [reusable] Mac T4, C-MAC® S [single-use] Macintosh #4, C-MAC® [reusable] Macintosh #4) together with one direct laryngoscope (Heine LED). Each laryngoscope was assessed with three measurements, as follows: part 1: illuminance (lux) was measured in situ using a purpose-designed benchtop light intensity measurement apparatus; part 2: luminance (light reflected back to the eye) was measured (in candela m-2 [cd·m−2]) during videolaryngoscopy (VL) and DL in a human cadaver using a spot meter pointed at the interarytenoid notch; part 3: illuminance (lux) was measured during VL and DL in a human cadaver using a light meter surgically implanted just proximal to the vocal cords.

Results

Illuminance and luminance varied significantly among the Mac-VLs. Mean (standard devitation) illuminance among the six tested Mac-VLs ranged from 117 (11) to 2,626 (42) lux in the measurement apparatus and from 228 (11) to 2,900 (374) lux by the surgically implanted light meter in the cadaver. All values were less than the reference Heine direct laryngoscope and some fell below the published ISO standard of 500 lux for DL. Luminance testing by spot meter had a similarly wide range, varying from 3.78 (0.60) to 49.1 (10.4) cd·m−2, with some Mac-VLs delivering less luminance than the reference Heine direct laryngoscope.

Conclusions

Our results indicate that illuminance and luminance provided by Mac-VLs used for direct laryngeal viewing varies substantially between devices, with some falling below standards previously suggested as the minimum required for DL. While this may have no implications for the quality of image visible on a device’s video monitor, the clinician should be aware that when Mac-VLs are used for direct viewing of the larynx, lighting may not be optimal. This might adversely affect ease or success of tracheal intubation.

Résumé

Contexte

L’éclairage adéquat du larynx est nécessaire pendant la laryngoscopie pour faciliter l’intubation trachéale. Pour la laryngoscopie directe (LD), l’Organisation internationale de normalisation (ISO) a établi une intensité lumineuse minimale de plus de 500 lux pendant au moins dix minutes. Toutefois, il n’existe aucune norme de ce type pour les lames de vidéolaryngoscope à géométrie Macintosh (VL-Mac), qui permettent une visualisation directe ou indirecte (vidéoscopique) du larynx. Par des études en laboratoire et in vitro sur un cadavre humain, nous avons déterminé les valeurs d’éclairage et de luminance fournies par divers VL-Mac et les avons comparées aux valeurs repères d’éclairage minimal publiées ainsi qu’aux valeurs obtenues avec un laryngoscope direct de référence.

Méthode

Nous avons testé six VL-Mac (i-view™, McGRATH™ MAC, GlideScope® Spectrum™ [à usage unique] DVM S4, GlideScope® Titanium [réutilisable] Mac T4, C-MAC® S [à usage unique] Macintosh #4, et C-MAC® [réutilisable] Macintosh #4) ainsi qu’un laryngoscope direct (Heine LED). Chaque laryngoscope a été évalué avec trois mesures, comme suit : partie 1: l’éclairage (lux) a été mesuré in situ à l’aide d’un appareil spécialement conçu de mesure de l’intensité lumineuse en laboratoire; partie 2 : la luminance (lumière réfléchie vers l’œil) a été mesurée (en candela m-2 [cd·m-2]) pendant la vidéolaryngoscopie (VL) et la LD sur un cadavre humain, à l’aide d’un posemètre pointé vers la commissure interaryténoïdienne; partie 3: l’éclairage (lux) a été mesuré pendant la VL et la LD sur un cadavre humain à l’aide d’un photomètre implanté chirurgicalement juste en amont des cordes vocales.

Résultats

L’éclairage et la luminance variaient considérablement entre les VL-Mac. L’éclairage moyen (écart type) parmi les six VL-Mac testés variait de 117 (11) à 2626 (42) lux avec l’appareil de mesure, et de 228 (11) à 2900 (374) lux lorsque mesuré par le photomètre implanté chirurgicalement dans le cadavre. Toutes les valeurs étaient inférieures au laryngoscope direct Heine de référence, et certaines étaient inférieures à la norme ISO publiée de 500 lux pour la LD. Les essais de luminance par posemètre ont rapporté une plage tout aussi large, variant de 3,78 (0,60) à 49,1 (10,4) cd·m-2, certains VL-Mac offrant moins de luminance que le laryngoscope direct Heine de référence.

Conclusion

Nos résultats indiquent que l’éclairage et la luminance fournis par les VL-Mac utilisés pour la visualisation directe du larynx varient considérablement d’un appareil à l’autre, certains tombant en dessous des normes précédemment suggérées comme minimalement requises pour la LD. Bien que cela puisse n’avoir aucune incidence sur la qualité de l’image visible sur le moniteur vidéo d’un appareil, le clinicien doit être conscient que lorsqu’un VL-Mac est utilisé pour la visualisation directe du larynx, l’éclairage pourrait ne pas être optimal. Cela pourrait nuire à la facilité ou au succès de l’intubation trachéale.

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Author contributions

Madeleine Harlow contributed to data acquisition and writing and critically revising the article. George Kovacs contributed to study conception and design and data acquisition, analysis and interpretation. Paul Brousseau contributed to testing of devices in table-top apparatus and writing and critically revising the article. J. Adam Law contributed to writing and critically revising the article.

Acknowledgements

The authors would like to acknowledge and thank Dr. Sean MacKinnon and Dr. Tiberiu Mahu for their help with statistical analysis.

Disclosures

Kovacs and Law: Course co-directors of Airway Interventions and Management in Emergenices (AIME) course and partner in parent company AIME Training Inc. Recipient of equipment as loan or donation from Verathon, Ambu, Karl Storz and Covidien.

Funding statement

Funding supported in part by the Departments of Emergency Medicine (Kovacs) and Anesthesia, Pain Management and Perioperative Medicine (Law), Dalhousie University.

Editorial responsibility

This submission was handled by Dr. Stephan K.W. Schwarz, Editor-in-Chief, Canadian Journal of Anesthesia/Journal canadien d’anesthésie.

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Correspondence to J. Adam Law MD, FRCPC.

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Appendix: Identification numbers of tested devices

Appendix: Identification numbers of tested devices

Device Identification
GlideScope T4 titanium blade Made by: Verathon
S/N: LD151507
https://www.verathon.com/glidescope-titanium-reusable/
GlideScope (Plastic) Spectrum MAC S4 Made by: Verathon
REF: 0574-0179
LOT: GR36189
https://www.verathon.com/glidescope-spectrum-single-use/
McGRATH MAC: MAC 4 disposable laryngoscope blade Made by: Medtronic
LOT: 18031601
https://www.medtronic.com/covidien/en-us/products/intubation/mcgrath-mac-video-laryngoscope.html
Karl Storz: C-MAC monitor 8403 ZX Made by: Karl Storz
SN ZR18032
https://www.airwayworld.com/karl-storz-products/
C-MAC S videolaryngoscope blade MAC #4 Made by: Karl Storz
REF: 051114-01
LOT: 161111
https://www.airwayworld.com/wp-content/uploads/2013/08/2.-C-MAC-SINGLE-USE.pdf
https://www.airwayworld.com/wp-content/uploads/2013/08/1.-C-MAC-VIDEO-LARYNGOSCOPES.pdf
i-view videolaryngoscope Made by: Intersurgical
8008000-9-A 2094 Issue 1 JMT 03.17
https://www.intersurgical.com/info/iview
Heine LED Laryngoscope Made by: Heine Anesthetic
Sekionic Lightmaster PRO L-478D Made by: Sekonic
ID: X001NWU9N3
https://www.sekonic.com/united-states/products/l-478d-u/features.aspx
Tenma light meter Made by: MCM Electronics
Spotmeter M Made by: Minolta

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Harlow, M., Kovacs, G., Brousseau, P. et al. An in vitro assessment of light intensity provided during direct laryngeal visualization by videolaryngoscopes with Macintosh geometry blades. Can J Anesth/J Can Anesth (2021). https://doi.org/10.1007/s12630-021-02099-8

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Keywords

  • Illumination
  • Illuminance
  • Laryngoscopy
  • Luminance
  • Light
  • Videolaryngoscope