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.

The bougie – is it immortal?

Despite the technique of using an introducer to facilitate intubation being described over 65 years ago, the bougie, or tracheal tube introducer, remains a popular airway adjunct. With the development of more hi-tech aids to manage the airway, such as video laryngoscopes, is the demise of the bougie imminent or is it destined for immortality?

As Dr J J Henderson confirmed in correspondence entitled, ‘Development of the gum-elastic bougie’ - published in Anaesthesia in 2003, although Robert Reynolds Macintosh, who designed the Macintosh Laryngoscope – described by Sir Anthony Jephcott  as, ‘the most numerously and widely made durable item in the history of anaesthesia’ – is usually given credit for the first use of introducers to facilitate tracheal intubation, the technique was described a year earlier by Minnitt & Gillies in their ‘Textbook of Anaesthetics’, published by E & S Livingstone Ltd in 1948.

Dr Henderson confirms that in relation to passage of a tracheal tube with the Macintosh laryngoscope, the Minnitt & Gillies publication suggested, ‘This is an easy matter when a semi-rigid gum elastic catheter is passed’. 

 Sir Robert Macintosh (1897 – 1989), knighted in 1955, described the technique in his landmark illustrated 1949 article entitled, ‘An aid to oral intubation’ as follows:

 ‘One of the difficulties in passing tubes beyond a certain size is that the body of the tube obscures the view of the cords through which the tip must be directed. In order to overcome this I thread the tube over a long gum-elastic catheter, the tip of which is then passed through the cords under direct vision. Using the catheter as a guide, the tube is gently pushed down into position and the guide is then withdrawn.’

A few years later in 1952, responding to correspondence from a Dr Rook, Barnard (Anaesthesia 1952;7:119) described a technique he found of practical value when for any reason intubation proved difficult:

‘A small gum-elastic bougie is pushed through the Magill’s tube until about two inches extend beyond the distal end. The bougie is then bent forwards at an angle of 45 degrees or less. A Macintosh’s laryngoscope is passed and the bougie is passed through the larynx. The Magill’s tube is then passed well into the trachea and the bougie is removed’.

Use was not widespread until after the introduction of the Endotracheal Tube Introducer by Eschmann Bros & Walsh Ltd in the 1970s. This device incorporated a coudé tip, one of a number of differences to the device originally described by Macintosh in 1949. Dr Venn, who designed the device whilst working as an anaesthetic advisor to Eschmann, has described the development of the bougie in correspondence published in Anaesthesia in 1993 and the story was expanded further by Dr Henderson, from additional information provided by Dr Venn, in an article entitled, ‘Development of the gum-elastic bougie’ published in the same journal ten years later.

One irony is, as El-Orbany et al noted in Anesthesiology in 2004, the Eschmann Tracheal Tube Introducer is not gum, elastic or a bougie. The gum elastic bougie was originally a urinary catheter designed for dilation of urethral strictures. The material of the Eschmann device was different in that it had two layers: a core of tube woven from polyester threads and an outer resin layer. Other differences were the length, longer at 60cm, to allow the railroading of an endotracheal tube and the ‘presence of a 35 degree curved tip, permitting it to be steered around obstacles’.

Since its introduction, the bougie, or tracheal tube introducer, has grown in popularity, and whilst an equipment list for management of the difficult airway might include a number of different types of devices and airway adjuncts, such as alternative styles of rigid laryngoscope blades, supraglottic airways, video laryngoscopes and flexible fibreoptic intubation equipment, it is also likely to include some form of tracheal tube introducer or guide – single use or reusable.

The Difficult Airway Society (DAS) 2005 list of recommended equipment for routine airway management includes a ‘Tracheal tube introducer (gum-elastic-bougie)’ and an ‘Introducer (bougie)’ is included as part of ‘Plan A: Initial tracheal intubation plan’ in the DAS algorithm for ‘Unanticipated difficult tracheal intubation – during routine induction of anaesthesia in an adult patient’. Intubating bougies are also mentioned in the section on Recommendations for Extubation in the ‘Practice Guidelines for Management of the Difficult Airway’ , an updated report by the American Society of Anesthesiologists (ASA) Task Force on Management of the Difficult Airway, published in 2013.

Single use alternatives from a variety of manufacturers have been available for a number of years, and the Association of Anaesthetists of Great Britain and Ireland (AAGBI) Safety Guideline document, Infection Control in Anaesthesia, published in 2008, states:

Bougies: ‘Re-use of these items has been associated with cross-infection. Manufacturers recommend that a gum elastic bougie may be disinfected up to five times between patients and stored in a sealed packet. It is preferable that alternative single-use intubation aids are employed where possible.’

Even a cursory search of the published literature relating to tracheal tube introducers produces literally hundreds of studies, case reports and correspondence, comparing different types of introducers and a variety of potential extended applications, as well as the effects of sterilisation on multi-use devices, (Anaesthesia, 2011, 66, pages 1134 – 1139), and the forces required to remove bougies from tracheal tubes (Anaesthesia, 2009, 64, pages 320 – 322). There is even a report, published in Anaesthesia in 2007, regarding a home-made bougie. A quite alarming story in this modern age of device regulation, the author describes fashioning a bougie in Indonesia from a wire coat hanger and an ordinary giving set whilst waiting for a bougie to arrive from England! The author used the device on more than 40 occasions, commenting that, ‘In four patients I do not think I would have been able to intubate the trachea without it.’

It seems the bougie continues to be perceived as a useful airway adjunct for the persistent epiglottis-only view, but as Dr Richard Levitan has described in his overview of the Bougie (Tube Introducer), ‘The bougie is not a heat seeking missile, i.e., it does not ‘find’ the trachea automatically; laryngeal landmarks, i.e. the epiglottis at a minimum, or preferably the posterior cartilages must be sighted to place the bougie in the trachea.’

Given that many airway conferences now often include a debate comparing direct laryngoscopy to video laryngoscopy and provocatively ask whether the days of the standard laryngoscope are numbered, it is interesting that even those who feel the value of a bougie may sometimes be overstated, do not seem to suggest the bougie is in imminent danger of being consigned to the history books as a relic of anaesthesia practice from days gone by. Perhaps the bougie is immortal?

REVIVE airway study – clinical outcomes and future plans

Since plans were first announced to conduct a randomised comparison of two second generation SADs to current practice in the initial airway management of out-of-hospital cardiac arrest (OHCA) in a UK ambulance service, the results have been eagerly anticipated. This can be no surprise given the paucity of high level evidence to confirm the best technique for maintaining an airway and providing ventilation in adults with cardiopulmonary arrest.

However, the primary objective of REVIVE was not to provide a definitive answer to the above question, but to assess the feasibility of the study design. If REVIVE proved the design was feasible, capable of establishing whether ventilation success can be achieved, and of measuring other key outcomes such as return of spontaneous ventilation and survival to hospital, then it would lay the foundation for a future full-scale study which might just provide us with the answer to the above question.

The REVIVE airway working group presented a poster at the International Conference on Emergency Medicine (ICEM) in Dublin in June last year entitled, ‘Early report of paramedic recruitment in the REVIVE-Airways study’. This confirmed the target of recruiting 150 randomised paramedics and stratification by experience and base station location had been successfully achieved.

Last month, in an abstract presented at the American Heart Association Resuscitation Science Symposium in Dallas, we had our first glimpse of the data related to the clinical outcomes. As this was a feasibility trial and not designed or powered to show clinically significant differences between each device or study arm, there was some discussion as to whether the clinical data should be released. However, the protocol published in the British Medical Journal (BMJ), suggests the original intention had always been to disseminate the clincial data to participants in the study and to the wider public via an open access web-site, appropriate conferences and medical journals.

A more comprehensive overview of the study results was presented at the UWE Conference & Exhibition Centre in Bristol on the 29th November. Speakers included Dr Jerry Nolan, Dr Jas Soar, Prof Jonathan Benger, Dr Matt Thomas, Dr Janet Brandling, Dr Sarah Voss and Mr Dave Coates.

The results showed no significant differences in important clinical outcomes between the use of a supraglottic airway (SAD) and usual practice (principally tracheal intubation) during OHCA. However, the trial was insufficiently powered to detect small differences in mortality. The i-gel® was superior to the LMA Supreme® on several measures, including compliance, adverse events and staff feedback. The investigators are proceeding to a large-scale trial of i-gel® versus tracheal intubation in OHCA.

For the record, the survival to hospital discharge was as follows:

     • i-gel® 10.3%
     • LMA Supreme® 8.0%
     • Usual practice 9.1%

     (p=0.73)

Survival to 90 days is shown below:

     • i-gel® 9.5%
     • LMA Supreme® 6.9%
     • Usual practice 8.6%

     (p=0.65)

Data was also presented on neurocognitive and quality of life outcomes, as well as successful device placement. There was also interesting data regarding the number of arrests attended by each paramedic (March 2012 to February 2013), which ranged from 0-11, with a mean of 3.6 arrests per paramedic. 15 paramedics did not attend any arrest during the study period. There were presentations confirming how the airway was actually managed in practice and feedback from the paramedics that participated in the study.

Successful aspects of REVIVE included proof of the feasibility of a cluster randomised trial of airway intervention in OHCA and the collection of valuable data to inform a full trial. It also demonstrated the strong support of paramedics and informed statistical calculations for a larger study. So, what next?

REVIVE 2

Professor Jonathan Benger, in a presentation entitled, ‘Further research: REVIVE 2′, confirmed the aims of REVIVE 2 as identifying differences in the primary outcome of modified Rankin Scale (mRS) at hospital discharge: good recovery (0-3) versus poor recovery/death (4-6) and differences in:

• mRS at 3 and 6 months following OHCA
• Quality of life at discharge, 3 months and 6 months
• Cognitive function at 3 and 6 months
• ROSC
• Length of stay
• Ventilation success, regurgitation and aspiration
• Loss of a previously established airway

Comparative cost effectiveness of the i-gel® and intubation, as well as the views and preferences of paramedics is also to be assessed.

It is intended the design will be a cluster randomised trial (by paramedic), with an airway algorithm for each arm. Clinical need will always take precedence and there will be an economic analysis, as well as patient and public involvement. An outline bid has been successful, and a full proposal is to follow (5th February 2014). It is intended for the trial to run for 45 months, from October 2014 to June 2018.

REVIVE 2 will need approximately 1,300 paramedics. This will probably require the inclusion of three or four large UK ambulance trusts. It is estimated the cost for REVIVE 2 will be £2 million. The investigators are ready to begin.

Four and a half years (probably 5 years before the results are reported) may seem a long time to wait for the conclusion of REVIVE 2, but given the lack of high level data currently available regarding the best airway device to use during the initial phase of OHCA, it will be worth the wait.

Passive oxygenation – the jury is still out

As discussed in my blog post from April 2012, ‘Should we be passive about oxygenation?’, in the years preceding the issue of the 2010 European Resuscitation Council (ERC) and Amercian Heart Association (AHA) guidelines on resuscitation, interest in the concept of passive oxygenation, particularly as a component of CardioCerebral Resuscitation (CCR) protocols, appeared to peak. This led to considerable speculation as to how the International Liaison Committee on Resuscitation (ILCOR) would assess the published evidence regarding passive oxygenation compared to standard ventilation techniques and what the subsequent recommendations would be in the new 2010 ERC and AHA guidelines.

In the end, the ERC concluded that, ‘There is insufficient evidence to support or refute the use of passive oxygen delivery during CPR to improve outcome when compared with oxygen delivery by positive pressure ventilation’, and the AHA that, ‘This time there is insufficient evidence to support the removal of ventilations from CPR performed by ACLS providers.’

It might reasonably have been expected that such conclusions would stimulate potential investigators to intensify their efforts to provide the additional evidence needed to enable more conclusive statements in the next set of guidelines, scheduled for issue in 2015. Disappointingly, this has not been the case, so the jury is still out, with little immediate prospect of having significant new evidence to consider.

There may be any number of reasons for this. One possibility is the debate regarding airway management and ventilation in CPR has simply moved on to other areas of interest, such as the optimal airway device. However, if so, it has progressed without really resolving the question of whether passive oxygenation has a useful role to play during CPR, particularly for the first few minutes following witnessed ventricular fibrillation/ventricular tachycardia (VF/VT).

A key question regarding the concept and viability of passive oxygenation as an alternative to standard ventilation during the initial phase of CPR has always been whether chest compressions generate adequate ventilation in cardiac arrest (providing there is a patent airway).

In the 2010 AHA guidelines for CPR (Part 8), in the section on passive oxygenation delivery during CPR, it is stated that:

‘Chest compressions cause air to be expelled from the chest and oxygen to be drawn into the chest passively due to the elastic recoil of the chest. In theory, because ventilation requirements are lower than normal during cardiac arrest, oxygen supplied by passive delivery is likely to be sufficient for several minutes after onset of cardiac arrest with a patent upper airway.’

In their article, ‘Airway techniques and ventilation strategies’, Nolan and Soar, comment that:

‘A study of 17 intubated patients in an emergency department who were undergoing chest compressions using a mechanical compression device (Lund University Cardiopulmonary Assist System (LUCAS)) showed that the median tidal volume per compression was just 42ml – considerably less than the dead space. These patients had been in cardiac arrest for more than 40 min, and therefore, their lung compliance was probably poor. Nevertheless, the implication is that chest compressions alone do not generate adequate ventilation. Despite this, and based partly on further animal data, a group from the Sarver Heart Center in Tucson, Arizona, the United States, has described the use of passive oxygenation insufflation as part of their protocol for CardioCerebral Resuscitation (CCR). This group has recently reported better survival to hospital discharge after witnessed VF cardiac arrest from adults who were managed initially with passive oxygenation (insertion of an oropharyngeal airway and oxygen given at 15L/min by non-rebreather mask) compared with those given active ventilation.’

Perhaps improvements in survival rates, such as those described above, have been due to factors other than passive oxygenation? Most of the studies on passive oxygenation have included multiple treatment changes and/or a number of confounders, so this remains a possibility.

Despite the lack of significant new data, passive oxygenation has continued to be a subject of discussion in a number of recent articles.

In a review article published in ‘Current Opinion in Critical Care’ (COCC), entitled, ‘Advanced life support and mechanical ventilation’, Kill, Dersch and Wulf discuss, amongst other topics, passive oxygenation versus active ventilation. They conclude that:

‘The total number of studies dealing with mechanical ventilation during resuscitation and ALS is still limited. The still recommended standard is positive-pressure ventilation with a tidal volume of 6-7ml/kg and a respiratory rate of 10/min, purse oxygen and preferably with a ventilator. During the first few minutes of CPR, passive oxygen insufflation via a nonrebreathable mask or an airway device might be an acceptable alternative. Hyper-oxygenation should be avoided once a spontaneous circulation is restored, and waveform capnometry is an important monitoring for both ventilation and perfusion of the lungs.’

In another review published in COCC in 2013, entitled, ‘Airway Management in cardiopulmonary resuscitation’, Soar and Nolan confirm that:

‘Some EMS system protocols for adult primary cardiac arrest include airway opening and high-flow face-mask oxygen, and passive oxygenation from chest compressions for the first 6 minutes of CPR. Improved outcomes have been reported with this ‘minimally interrupted’ CPR approach although further study is needed’. A retrospective analysis of adult OHCA patients reported improved neurologically intact survival after witnessed VF/VT OHCA with passive ventilation compared with bag-valve mask ventilation. Survival was similar for unwitnessed VF/VT and nonshockable rhythms. Observational data from large registries in Japan, however, suggest that ventilation is necessary during CPR in children, after cardiac arrest with a primary respiratory cause, and during a prolonged cardiac arrest.’

As well as delivery using a non-rebreather mask and oropharyngeal airway, passive oxygenation, or passive airway management™ (PAM), can be delivered via a supraglottic airway, such as the Intersurgical i-gel O2™, which incorporates a supplementary oxygen port specifically designed for this purpose (figure 1). Such a device may offer advantages over use of a non-rebreather mask, such as providing the opportunity to switch more seamlessly from passive oxygenation to standard ventilation, thereby minimising interruption to chest compressions. However, this is speculation only and has yet to be confirmed by any published evidence.

Connecting a standard oxygen tube to the supplementary port of the i-gel O2 in preparation for the delivery of passive oxygenation

Connecting a standard oxygen tube to the supplementary port of the i-gel O2 in preparation for the delivery of passive oxygenation

In conclusion, whilst there appears to be very little new published data, passive oxygenation remains a subject of lively debate in resuscitation circles and is often mentioned in articles reviewing ventilation strategies and airway management in cardiac arrest. Before it slips from view due to a lack of new evidence, it is hoped a new wave of studies are already in progress and will soon emerge as peer reviewed published studies in the near future, enabling a more conclusive assessment to be made as to whether passive oxygenation has a useful role to play during CPR. Without doubt, at the present time, the jury remains out.

I would be most interested to hear from anyone who is currently using a protocol which incorporates passive oxygenation, is involved in a study incorporating this technique or is looking to conduct such a study in the future.

Use of SADs in the prehospital setting – a new review

Ostermayer and Gausche-Hill, in their review paper, ‘Supraglottic airways: The history and current state of prehospital airway adjuncts’, to be published in Prehospital Emergency Care, provide a much welcome overview on the use of supraglottic airways (SADs) in what can often be a difficult and challenging setting.

The paper begins by confirming that the widespread adoption of SADs in prehospital care ‘directly stems from their ease of use, simplicity of training, predictability, and speed of insertion’. It continues with a brief history of the use of SADs, particularly the Laryngeal Mask Airway, in the prehospital setting and includes individual overviews of a number of devices, including the Combitube®, King LT®, LMA Fastrach® and Intersurgical i-gel®.

There is acknowledgement that whilst SADs do not, in the words of the authors, provide ‘definitive airway management’, some of the newer devices do incorporate higher seal pressures than earlier options and the ability for gastric decompression, which ‘may significantly decrease aspiration risk’.

In anaesthesia circles in particular, a new classification of SADs into 1st and 2nd generation devices has gained considerable popularity and helped to highlight important differences between devices. In a review article by White et al, entitled, ‘A critique of elective pediatric supraglottic airway 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.’

Of course, as mentioned in an earlier blog post on the classification of supraglottic airways, 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. These are important considerations when deciding the most appropriate SAD to use in the pre-hospital setting.

Discussion on the use of airway devices in the austere environment states that data collection from Combat Support Hospitals in 2008 demonstrated that 86.3% of prehospital managed airways were managed with an Endotracheal tube (ETT), 7.2% with an Esophageal Tracheal Combitube (ETC) and 0.7% with an LMA, and that, ‘although the ETC is the standard rescue airway device for the U.S. Army, poor skill retention has been demonstrated with the device among medics.’

RSA or Rapid Sequence Airway placement, the insertion of an alternative airway, such as a SAD, after pharmacological treatment with a paralytic and sedative is discussed. This is an important subject and Ostermayer and Gausche-Hill confirm that no trials have yet compared the risks and benefits of drug-assisted SAD placement to non-drug-assisted placement.

The final section of the review takes a look at airway management in Out-of-Hospital Cardiac Arrest (OHCA). Of particular interest is a reference to a Japanese study which looked at neurological outcomes in patients where an ETT was used, compared to either a SAD or Bag Valve Mask (BVM). The results are interesting, but it is important when reviewing such studies to consider the SADs that were used. Results are likely to be quite different for 2nd generation SADs such as the i-gel, compared to a 1st generation device such as a standard Laryngeal Mask Airway. In some countries like the UK, devices such as the Combitube® are now rarely, if ever used. This issue is discussed in more depth in my blog post, ‘Pre-hospital airway management for patients with OHCA’.

There are a couple of small errors in the ‘early view’ version of this paper. For example, in Table 1, the i-gel® is designated as reusable, whereas the device is in fact single use. No doubt these errors will be corrected in the final published version.

In summary, this review paper provides an interesting overview of the history and current state of prehospital airway adjuncts. The conclusion will reflect the thoughts of many with regard to this subject:

‘Since prehospital airway management devices largely evolve from the field of anesthesia, much of the medical literature regarding new devices focuses on the operating room. With the many obvious practical and clinical differences between these clinical settings, further studies in the prehospital environment are needed, specifically trials correlating neurologic outcome to supraglottic device’

Equally important will be to ensure that results for one type of SAD are not extrapolated to another with quite different design characteristics. Tempting as it may be to discuss SADs as if they are one homogenous group of devices, the reality, as this paper helps to highlight, is that the performance of each device can and will be quite different. One SAD is most definitely not the same as another. Further data regarding the use of SADs in the prehospital setting is eagerly awaited.

Use of SADs during neonatal resuscitation

In June this year, an interesting discussion article was published in Resuscitation by Schmölzer et al, entitled, ‘Supraglottic airway devices during neonatal resuscitation: An historical perspective, systematic review and meta-analysis of available clinical trials’.

This is a welcome review. Whilst The World Health Organisation (WHO) report that neonatal mortality rates have declined from 32 per 1,000 births in 1990 to 22 per 1,000 births in 2011, a reduction of over 30%, the proportion of child deaths which occur in the neonatal period has increased in all WHO regions over the last 20 years. In an analysis of neonatal mortality – situation and trends, WHO state that prematurity is the leading cause of newborn deaths and that up to two thirds of newborn deaths could be prevented if skilled health care workers perform effective health measures at birth and during the first week of life.

The WHO Guidelines on Basic Newborn Resuscitation 2012 confirm that globally, approximately a quarter of neonatal deaths are caused by birth asphyxia, defining birth asphyxia as the failure to initiate and sustain breathing at birth. The guidelines go on to state that ‘effective resuscitation at birth can prevent a large proportion of these deaths’.

Schmölzer et al state that the International Liaison Committee on Resuscitation (ILCOR) and various national guidelines all agree that, ‘mask ventilation is the cornerstone of respiratory support immediately after birth.’ However, delivery room studies have shown that mask ventilation is difficult and mask leak and airway obstruction are common. In light of this, it is interesting to consider, as Schmölzer et al have done, what role supraglottic airways might have in neonatal resuscitation and examine the current evidence base for their use.

Current neonatal guidelines, such as those issued by the American Heart Association (AHA), state that Laryngeal Mask Airways (LMs) have been shown to be effective for ventilating newborns weighing more than 2kg or delivered ≥ 34 weeks gestation, and that there are limited data on the use of these devices in small preterm infants <2kg or <34 weeks gestation. The AHA guidelines also confirm that, ‘A laryngeal mask should be considered if facemask ventilation is unsuccessful and tracheal intubation is unsuccessful or not feasible. The laryngeal mask has not been evaluated in cases of meconium-stained fluid, during chest compressions, or for administration of emergency intratracheal medications.’

Perhaps unsurprisingly, Trevisanuto et al reported that although 35% of Italian anaesthetists and 23% of paediatricians have experience with LMs for airway management in newborn infants, anaesthetists were more enthusiastic about the LM than paediatricians. Schmölzer et al confirmed that although there are various studies comparing LMs, randomised trials comparing the performance of each LM are warranted.

There is a meta-analysis of randomised trials (RCT) in the Schmölzer et al review, which concludes that, ‘Overall, RCTs have shown that initial respiratory support with a LM is feasible and safe. However, there is not enough evidence to recommend LM instead of mask ventilation for initial respiratory support in the delivery room and large randomised trials are warranted before the technique is widely applied.’

The review also discusses the potential of supraglottic airways as a conduit for the administration of surfactant. An important subject, particularly given that surfactant administration via an ET tube has been associated with a series of adverse events. The review notes that, ‘although pilot data are promising, the current available evidence suggests that surfactant administration via laryngeal mask should be limited to clinical trials.’

At the 54th Annual Meeting of the European Society for Paediatric Research in Porto in October this year, three posters are being presented regarding the use of supraglottic airways in neonatal resuscitation. The first is entitled, ‘The relationship between successful insertion of a neonatal sized i-gel and a health care provider’s profession or experience’, by Sugiura et al from Shizuoka, in Japan. The second, from the same group of investigators, is entitled, ‘Randomised controlled study comparing a neonatal sized i-gel and the Laryngeal Mask Airway in a neonatal resuscitation mannequin.’ The third is entitled, ‘Higher success rate and operator satisfaction with i-gel laryngeal mask airway compared to face mask: A mannequin study of neonatal resuscitation in Uganda’, by Pejovic et al, from Stockholm in Sweden, Padua in Italy, Kampala in Uganda and Bergen in Norway.

It will not be possible to draw any conclusions from these posters, so the authors will no doubt conclude that further research is required. Of significance is the potential benefits of using supraglottic airways during neonatal resuscitation compared to a BVM or ET tube being discussed and studied, and the recognition that all supraglottic airways are not the same.

The latter point is important. Evidence for one supraglottic airway should not be extrapolated to another device with different design characteristics.

Further data regarding the potential use of supraglottic airways in neonatal resuscitation is awaited with great interest.

Airway management in a combat zone

Most discussions regarding airway management probably relate to use of airway devices during anaesthesia, in-hospital and out-of-hospital cardiac arrest (OHCA) and Emergency Medicine (EM). Each of these disciplines presents its own challenges, but perhaps the most hostile and challenging environment in which to manage the airway is during combat by those involved in Special Operations Medicine (SOM).

A report published in the Spring 2013 edition of the Journal of Special Operations, entitled, Proposed Change: Supraglottic Airways Committee on Tactical Combat Casualty Care (CoTCCC) Recommendation Paper, included a review of the use of Endotracheal Intubation (ETI) v Supraglottic Airways (SGA) and Surgical Airways v SGAs.

Many of the discussion points regarding use of ETI v SGAs will be familiar to most civilian practitioners of airway management and much of the evidence presented in the paper relates to non-military, non-combat situations. However, the paper does note that ETI ‘has been reported to be accomplished by military physicians on the battlefield with a success rate comparable to that achieved in the civilian setting.’ It also makes the point that intubating a trauma patient without sedation and paralysis will be difficult and that training courses that emphasise use of ETI and SGAs, often don’t discuss how to intubate or insert an SGA in a non-comatose patient.

Referencing a 2011 study by Timmerman, the paper also highlights that ‘SGAs may not be well tolerated by casualties who are not unconscious and may not be effective in casualties with direct airway trauma. The ideal casualty for SGA use is one who is unconscious and has no direct maxillofacial or neck trauma.’

The section discussing Surgical Airways v SGA is particularly interesting. Clearly, airway management in combat is not the same as management of a cardiac arrest patient in a civilian setting. The most common cause of airway death in combat casualties is maxillofacial trauma, with the result that management of the airway may be ‘complicated by blood, distorted anatomy, and a struggling patient.’

Referencing the manual by Butler et al, entitled, Prehopsital Trauma Life Support Manual (7th edition) – Military Version, published in 2010, the paper states that , ‘Many casualties with isolated maxillofacial injury can protect their own airways by simply sitting up, leaning forward, spitting out the blood in their airway and continuing to breathe in that position. Surgical airways should be reserved for those casualties in whom this strategy is not successful at maintaining an adequate airway. Maxillofacial injury should not trigger a knee-jerk reflex for the medic to attempt a surgical airway.’ Nonetheless, the TCCC noted that a surgical airway was the airway procedure of choice in a combat casualty when the airway is compromised by direct maxillofacial trauma.

There is an interesting discussion regarding pre-hospital cricothyroidotomy and the records from the Joint Theater Trauma Registry, including the differences in failure rates for cricothyroidotomy between combat medics, physicians and physicians’ assistants and the caution that should be exhibited when interpreting this data. There is also a review of some of the published evidence regarding different types of SGA, including the Laryngeal Mask Airway, LMA ProSeal® , Combitube®, King LT and the i-gel. Inevitably, since this report was completed last year, additional evidence has been published regarding the civilian use of SGAs and ETI during cardiac arrest, which the committee may have wanted to include had it been available to them.

The conclusions of the report include the following:

  • The recommendation for supraglottic airway use in Tactical Evacuation Care should be expanded to include SGAs other than the Laryngeal Mask Airway and Combitube®.
  • Use of SGAs is recommended as both a combat medic and a combat paramedic skill.
  • Casualties who are unconscious from haemorrhagic shock or severe Traumatic Brain Injury (TBI) but who have not suffered direct airway trauma are likely to be the best candidates for SGAs among the combat wounded.
  • Casualties who are able to tolerate either ETI or SGA without sedation and paralysis are likely to have a poor prognosis.

Sadly, the latter refers to the point that the among the combat wounded, the most common causes of unconsciousness are haemorrhagic shock and severe TBI. Both associated with high mortality.

Clearly, there are many combat situations where management of the airway is best achieved by techniques other than insertion of an SGA. However, when use of an SGA is indicated or appropriate, it would seem sensible that the device should be one which can be reliably inserted quickly and easily, incorporates a gastric channel to reduce the risk of aspiration (compared to an SGA without a gastric channel) and has a high seal pressure. A 2nd generation SGA would therefore probably seem a more logical choice than a 1st generation SGA.

Whilst this paper concluded that the recommendation for supraglottic airway use in Tactical Evacuation Care should be expanded to include SGAs other than just the Laryngeal Mask Airway and Combitube®, it did not make any specific recommendation regarding use of 2nd generation devices. This may be an interesting area for the committee to consider in any future review.

The Journal of Special Operations Medicine web-site can be accessed at the following web address http://www.jsomonline.org