A proposal for updating the classification of SADs and a new scoring system

The scoring and classification of supraglottic airways (SADs) is an interesting topic and currently the subject of much debate.

In 2011, a paper by Cook and Howes entitled, Recent developments in efficacy and safety of supraglottic airway devices, published in Continuing Education in Anaesthesia, Critical Care and Pain, described a classification of SADs into 1st and 2nd generation devices. The simplicity of this classification had immediate appeal and it quickly became established as the most widely used method for classifying SADs.

In A critique of elective pediatric supraglottic airway devices by White, Cook and Stoddart, a 1st generation device was described as asimple airway tube’ and 2nd generation as a device that ‘incorporates specific design features to improve safety by protecting against regurgitation and aspiration’.

Numerous publications, presentations and reviews subsequently utilised this classification, including the seminal  NAP4 report, the 4th National Audit Project of the Royal College of Anaesthetists (RCoA) and the Difficult Airway Society (DAS) on ‘Major Complications of Airway Management in the United Kingdom’, which made a number of recommendations regarding the use of SADs, and in particular the use of 2nd generation devices.

Its use has not been confined to the UK. The term is widely understood, accepted and used internationally. However, the classification of SADs as either 1st or 2nd generation was not the first classification.

In 2004, A Proposed Classification and Scoring System for Supraglottic Sealing Airways: A Brief Review by Miller was published in Anesthesia & Analgesia. This categorised SADs by the sealing mechanism. Three primary groups were identified:

  • Cuffed perilaryngeal sealers – such as the laryngeal mask airway
  • Cuffed pharyngeal sealers – such as the Cuffed Oropharyngeal Airway (COPA™)
  • Uncuffed anatomically preshaped sealers – such as i-gel®

This classification was further subdivided, so cuffless perilaryngeal sealers could be either ‘directional’ or ‘non-directional’, and cuffed pharyngeal sealers could be designated as ‘with’ or ‘without’ oesophageal sealing. The sealing mechanisms were described in detail, in conjunction with force vectors, frictional force and whether a device was reusable or single-use; or incorporated a mechanism to provide additional protection against aspiration.

In 2009, five years after Miller’s paper, the International standard, ISO 11712:2009(E) Anaesthetic and respiratory equipment – Supralaryngeal airways and connectors was published. This standard included five classifications of supralaryngeal designs. Further details can be obtained from my 2012 blog post on the classification of SADs.

Whatever their merits or limitations, neither the classification in the international standard or Miller’s classification from 2004 ever enjoyed the same measure of popularity or widespread use currently evident for the categorisation in to 1st and 2nd generation. It is therefore particularly interesting to note a proposal by the originator of the 1st/2nd generation classification, Professor Cook, for an update in correspondence to the editor of the British Journal of Anaesthesia (BJA).

The proposal is to add the suffix ‘i’ to 1st or 2nd generation to indicate those devices which enable intubation (eg with success >50%) and then include ‘d’ for direct intubation and ‘g’ for guided intubation. The correspondence provides three examples of SADs classified in this manner, as follows:

  • cLMA – 1st generation ‘ig’
  • Intubating LMA – 1st generation ‘id, ig’
  • i-gel® – 2nd generation ‘ig’

Further discussion regarding an updated classification can be seen on the BJA Out of the blue E-letters archive. Alternative classifications have been proposed, including one by Michalek and Miller in, ‘Airway Management Evolution – In a search for an ideal extraglottic airway device.

The scoring, as opposed to the classification of SADs, also has an interesting history. Miller proposed a ‘provisional scoring of airways’ in his 2003 paper already discussed above. This identified desirable features of airways for routine use and then for each variable (easy insertion, seal for IPPV etc) assigned a score to each device. An updated version, also by Miller, along similar lines, appeared in the second chapter of the book, The i-gel supraglottic airway, edited by Michalek and Donaldson.

The most recent scoring of SADs appeared in a particularly interesting editorial entitled, ‘Time to abandon the ‘vintage’ laryngeal mask airway and adopt second-generation supraglottic devices as first choice’ by Cook and Kelly.

This editorial notes that SADs now have important roles beyond airway maintenance during routine low-risk surgery, including airway maintenance in obese and higher risk patients and airway management outside the operating theatre by experts and novices, most especially during cardiac arrest. Other examples are also provided.

As a result, the authors state it is worth considering ‘whether one device can be the best device for all such functions and perhaps considering whether some devices might no longer be needed. This discussion raises the question as to whether the cLMA (and equivalent SADs) have any role in modern airway practice or whether it is time to move on.’

The editorial discusses a number of interesting and important issues related to the use of SADs, including the question of safety and efficacy, what sort of evidence should be sought when deciding which SAD to select – particularly if safety is the major concern – and the value and limitations of randomised controlled trials in answering safety related questions. Other issues of importance are also discussed, so it is critical the editorial is read in its entirety to fully appreciate the context in which the scoring system included in the paper is provided.

The scoring system itself lists the desirable features of a SAD (airway seal, overall insertion success, aspiration protection, avoiding sore throat etc) for a specific application (routine use during elective anaesthesia, use by a novice at a cardiac arrest etc), provides a maximal score for each parameter according to its importance and then allocates a score for each parameter for each device.

The authors confirm the ranking and allocated scores are based on their judgement, clinical experience and knowledge of the literature and also acknowledge that others may allocate maximal and relative scores differently.

I will not spoil your enjoyment of this editorial by revealing the results here, except to say the authors comment that, in the tables provided, it is notable that different circumstances lead to different SADs ranking highest and that ‘the cLMA rarely ranks highly in such analyses.’

The four scoring tables provided are as follows:

  • Table One: Choice of airway for routine use during elective anaesthesia
  • Table Two: Choice of airway for use by a novice at a cardiac arrest
  • Table Three: Choice of airway for expert rescue after failed intubation during rapid sequence induction
  • Table Four: Choice of airway for rescue after failed intubation followed by intubation through the SAD

In summary, a number of methods for classifying and scoring SADs have been proposed over the years. The most popular and widely used classification remains the categorisation of SADs as either 1st or 2nd generation. An update to this classification has been proposed to indicate those devices which enable intubation and a new scoring system has been published as part of an editorial in the BJA.

i-gel is a registered trademark of Intersurgical Ltd. cLMA is an abbreviation for the LMA Classic. LMA and LMA Classic are registered trademarks of Teleflex Incorporated or its affiliates. COPA is a trademark of Mallinckrodt Medical, Inc.

Classification of supraglottic airways

Early classification and scoring systems for supraglottic airways
In recent years, a number of attempts have been made to categorise supraglottic airways (SADs). In 2004, A Proposed Classification and Scoring System for Supraglottic Sealing Airways: A Brief Review by Miller was published in Anesthesia & Analgesia. This categorised SADs by the sealing mechanism. Three primary groups were identified:

  • Cuffed perilaryngeal sealers – such as the Laryngeal Mask Airway®
  • Cuffed pharyngeal sealers – such as the Cuffed Oropharyngeal Airway (COPA®)
  • Uncuffed anatomically preshaped sealers – such as i-gel®

This classification was further subdivided, so cuffless perilaryngeal sealers could be either ‘directional’ or ‘non-directional’, and cuffed pharyngeal sealers could be designated as ‘with’ or ‘without’ oesophageal sealing. The sealing mechanisms were described in detail, in conjunction with force vectors, frictional force and whether a device was reusable or single-use; or incorporated a mechanism to provide additional protection against aspiration. Whatever the merits of this system, it now appears unnecessarily complex, although to be fair, Miller’s objective was limited to providing a consistent method for evaluating and understanding the mechanisms of action of any given SAD.

In the same paper, Miller provided a provisional scoring of airways, which suggested a number of desirable features appropriate for a SAD for routine use in anaesthesia. This included easy insertion by a non-specialist, stable airway once positioned, sufficient sealing quality to apply positive pressure ventilation, a good first-time insertion success rate, minimal associated risk of aspiration, and minimal risk of cross-infection and serious side effects. These attributes remain valid today, although to this list we could probably now add latex free and atraumatic, requiring minimal training for safe and effective use, incorporation of a bite block, MRI compatibility, and perhaps suitability for use as a conduit for intubation.

International standard for supralaryngeal airways
In 2009, five years after Miller’s paper, the International standard, ISO 11712:2009(E) Anaesthetic and respiratory equipment – Supralaryngeal airways and connectors was published. This standard included five classifications of supralaryngeal designs as follows:

  • Cuffed oropharyngeal airway, where the ventilatory opening is located at the base of the tongue and a sealing surface is located in the oropharynx.
  • Laryngeal masks, where the ventilatory opening is surrounded by the cuff, which forms a seal with the periglottic tissues. The ventilatory opening and the cuff seal usually represent the most distal portion of the device.
  • Pharyngeal or pharyngeal-esophageal tube, where a cuff surrounds the ventilatory tube in a circumferential fashion and is located proximal to the ventilatory opening. This design compartmentalizes the pharynx, with the cuff serving as a sealing divider between the proximal and distal pharyngeal compartments, and the ventilatory opening(s) are located in the distal pharyngeal compartment.
  • Pharyngeal airway liner, which is represented by the streamlined liner pharyngeal airway (SLIPATM). This is a shell-like device that, upon insertion, expands the soft tissues of the neck. The tension of the elastic neck soft tissues that surround the device provides the sealing mechanism. The ventilatory opening is located within the shell in the periglottic area.
  • Device with a soft, gel-like, non-inflatable cuff and widened, concaved buccal cavity stabiliser. The sealing mechanism is created by the soft non-inflatable cuff accurately mirroring the anatomy of the laryngeal inlet to create an impression fit, without the need for cuff inflation.

 This classification did little to reduce complexity.

 1st and 2nd generation devices
In the same year as ISO 11712 was published,  White, Cook and Stoddart, in a review article published in  ‘Pediatric Anesthesia’, entitled, A critique of elective pediatric supraglottic airway devices categorised SADs into 1st and 2nd generation devices. A 1st generation device was described as a ‘simple airway tube’ and 2nd generation as a device that ‘incorporates specific design features to improve safety by protecting against regurgitation and aspiration’. I am not sure if this was the first published description of this method of classification, but its simplicity had immediate appeal, and it quickly became established as the most popular method for classifying SADs.

 It has since been used in numerous published clinical studies, review articles and conference lectures and a number of recommendations regarding use of 2nd generation devices were made in the 4th National Audit Project of the Royal College of Anaesthetists (RCoA) and The Difficult Airway Society (DAS) report, Major complications of airway management in the United Kingdom.

Of course, 2nd generation devices are not all the same, so the clinical evidence for each device regarding safety and efficacy still needs to be reviewed and assessed individually. Designation as a 2nd generation device does not in itself confirm superiority of performance, but the classification does provide useful information about basic product design characteristics, such as whether the device incorporates a mechanism for the management of regurgitant fluid.

In conclusion, although initial classifications of SADs provided some useful information, they were also complex, and as a result never really obtained widespread use or acceptance. The more recent classification of SADs into 1st or 2nd generation devices has proved popular, is widely used and provides valuable information regarding basic product design. Safety and efficacy of individual devices still needs to be reviewed and assessed individually.

A basic diagram highlighting the differences between 1st and 2nd generation devices is shown below (Fig 1). An Infographic, with additional background information, is also available (Fig 2). Please contact me if you would like a pdf copy of the infographic.

Fig 1

Fig 2 – Infographic