The Macintosh laryngoscope – is there a pretender to the crown?

Over 70 years after Sir R R Macintosh first described it in his landmark study published in The Lancet in 1943, the Macintosh laryngoscope remains universally popular.

Intersurgical plastic single use Macintosh laryngoscope blade, InterForm stylet and InTube ET tube

The dominant position of the Macintosh cannot be attributed to a lack of alternatives. Dorsch and Dorsch, in their huge 1,000+ page book, Understanding anesthesia equipment, list over 45 types of laryngoscope blade. Although some of these are described as modifications of the Macintosh, including the Oxiport Macintosh, Polio, Fink, Tull Macintosh, Bizarri-Giuffrida, Upsher Low Profile, Upsher ULX Macintosh, Improved vision Macintosh and the Left handed Macintosh, the list of alternatives also includes a significant number of other designs, including the Wisconsin, Schapira, Soper, Guedel, Bennett, Seward, Phillips, Alberts, Robertshaw and the Bainton. This list is not exhaustive. If you don’t have easy access to a copy of Dorsch & Dorsch, an extract is included in Annex D of the international standard, ISO 7376:2009: Anaesthetic and respiratory equipment – Laryngoscopes for tracheal intubation.

 In current practice, the two major types of Macintosh blade are generally considered to be the American, also called the ‘standard’, and the English, sometimes known as the ‘classic’ or ‘e-type’. The latter description is a particular favourite, conjuring up the image of the classic E-Type Jaguar, once described by Enzo Ferrari as, ‘The most beautiful car ever made’. Such a comparison may seem a little tenuous, but surely they can both be considered design classics?

The primary differences between the English or German and the American Macintosh are the shape, height and length of the proximal flange and the distance from the light to blade tip. The performance of both types was compared in a 2003 study by Asai et al, published in the British Journal of Anaesthesia, entitled ‘Comparison of two Macintosh laryngoscope blades in 300 patients.’ There was a difference in the view of the glottis in 80 patients. Among these patients, the view was better for the English blade for 63 patients and the standard blade was better for 17 patients. The authors concluded, ‘In patients in whom laryngoscopy was unexpectedly difficult, the English blade provided a better glottic view significantly more frequently than the standard blade.’

Probably the closest rival to the Macintosh in terms of popularity is the Miller blade. Described two years earlier than the Macintosh, the 1941 paper by Miller in Anesthesiology and simply entitled, ‘A new laryngoscope’, described a straight blade which when compared to an ‘old style medium sized blade’, was ’rounded on the bottom, smaller at the tip, and has an extra curve beginning about two inches from the end. The internal diameter of the base is shallow, but adequate to permit the passage of a 38 catheter.’ This landmark study is free to access on the Anesthesiology web-site. Miller also described a modification of his adult laryngoscope for children in 1946, ‘A new laryngoscope for intubation of infants’, Anesthesiology. 7(2):205, March 1946. This paper is also free to access.

The Miller blade remains popular for children, with straight blades in general having been described as ‘superior in elevating the tongue, removing it from the field of view to facilitate a better visualization of the infant larynx than the curved blade laryngoscope’. Doherty JS et al, 2009. Pediatric Anesthesia, 19: 30–37.

 In 2009, The UK NHS Purchasing & Supply Agency’s Centre for Evidence-based Purchasing (CEP) produced a  Buyer’s Guide for Laryngoscopes (CEP08048). The scope of this guide only extended to Macintosh blades sizes 3 and 4. No Miller or other alternative blades were included, perhaps reflecting the fact that ‘The Macintosh is the most popular [blade] for use with adults in the United Kingdom…’

 In the UK 4th National Audit Project (NAP4) – Major complications of airway management in the UK, it is confirmed in relation to tracheal intubation that, ‘Direct laryngoscopy with a Macintosh blade remains the technique of first choice if not actively contraindicated when difficulty is not anticipated.’

 Intersurgical single use plastic Macintosh laryngoscope blade

Given the huge variety of options available, why is the popularity of the Macintosh so enduring?

 Scott and Baker provide some answers in their 2009 review article, How did the Macintosh laryngoscope become so popular? In a very informative and entertaining article, the authors, New Zealanders like Macintosh, suggest that poor straight blade laryngoscopy technique prior to the widespread use of muscle relaxants, commercial availability, Macintosh’s connections in the industrial sector and unprecedented influence on the development of anaesthesia, as key factors in the success of the Macintosh blade that can be traced back to ‘prevailing circumstances’ in the 1940s. They conclude that, ‘Despite being able to achieve superior laryngoscopy with paraglossal straight blade technique and the multiple alternatives available, the Macintosh laryngoscope remains ubiquitous and is regarded as the gold standard of direct laryngoscopy’.

 In 1984, over 40 years after publication of the original description of the Macintosh laryngoscope and 25 years before the review article published by Scott and Baker, Jephcott published  A historical note on its clinical and commercial development. It was estimated by Jephcott that well over 1 million Macintosh blades had been made and sold in the previous 40 years. With regard to the origin of the design, Jephcott confirmed Macintosh’s own account from a letter he received from him:

 “I had a bit of luck and the nous to take advantage of it. On opening a patient’s mouth with a Boyle-Davis gag I found the cords perfectly displayed. Richard Salt (a really excellent chap) was in the theatre with me: before the morning had finished he had gone out and soldered a Davis blade on to a laryngoscope handle and this functioned quite adequately as a laryngoscope. The important point being that the tip finishes up proximal to the epiglottis.” Interestingly, he continued by noting that, ‘The curve, although convenient when intubating with naturally curved tubes, is not of primary importance as I emphasised subsequently.’

 Jephcott confirms the Macintosh laryngoscope was originally produced by Medical and Industrial Equipment Ltd (MIE), quickly followed by The Longworth Scientific Instrument Company Ltd. In the USA, Foregger of New York started to make the device in 1943. Jephcott concluded his article by noting that, ‘Today the Macintosh laryngoscope is known throughout the world and is made by many firms in many countries. The technique discovered by Macintosh and the instrument he designed for its achievement has survived translation into plastic and the adoption of the fibre-light. No doubt they will endure other developments in years to come.’

 Jephcott’s prediction was correct. Since his article in 1984, the Macintosh blade has also survived translation in to single use metal blades and is incorporated in to the design of a number of video laryngoscopes. The Macintosh blade remains the dominant blade for direct laryngoscopy in the 21st century, with no obvious pretender to the crown.

Advertisements