Airways-2

CPR2As we wait for the new 2015 guidelines for resuscitation later this year, the protocol for a major study which should be completed in time for inclusion in the evidence review for the 2020 guidelines is now available on-line.

‘Project portfolio HTA 12/167/102, Cluster randomised trial of the clinical and cost effectiveness of the i-gel supraglottic airway device versus tracheal intubation in the initial airway management of out of hospital cardiac arrest (Airways-2)’

Just over a year ago I uploaded a blog post entitled, REVIVE airway study – clinical outcomes and future plans. As well as reviewing REVIVE 1, the article discussed the future plans for REVIVE 2, now called AIRWAYS-2. Publication is expected in 2019, which if realised, will allow the study to be considered as part of the 2020 ILCOR Scientific Evidence Evaluation and Review System (SEERS) process.

Why is this trial important? Well, AIRWAYS-2 is an attempt to provide the type of high quality evidence called for back in 2009 by Nolan and Lockey in an editorial entitled, ‘Airway management for OHCA – more data required’. In this editorial, the authors commented that, ‘Virtually all the existing data relating to the use of SADs in cardiac arrest are derived from low-level studies. There is an urgent need for high-quality randomised controlled trials of the use of SADs for CPR.’ However, such studies are not easy to perform in the pre-hospital setting.

The AIRWAYS-2 trial summary confirms that:

 ‘There is real uncertainty amongst paramedics and experts in the field about the best method to ensure a clear airway during the early stages of OHCA. We therefore propose to undertake a large research study to determine whether intubation or the best available SAD (called the i‐gel) gives the best chance of recovery following OHCA.’

Paramedics from the following four English NHS ambulance services will participate:

  • South Western Ambulance Service NHS Foundation Trust (SWAST)
  • East of England Ambulance Service NHS Trust
  • East Midlands Ambulance Service NHS Trust
  • Yorkshire Ambulance Service NHS Trust

 As randomisation by patient is impractical in the pre-hospital emergency setting, randomisation will be by paramedic. The trial population will include adults who have suffered an OHCA that is not due to trauma. Patient exclusion criteria includes an estimated weight <50kg and a mouth opening of <2cm.

The trial intervention control group is the current standard care pathway: Tracheal intubation. The Intervention group (i-gel) is referred to as follows:

 ‘Because of its speed and ease of insertion, and the fact that it does not require a cuff to be inflated, the i‐gel has emerged as the preferred SAD for use during OHCA in Europe.’

 The aim and objectives of the study are confirmed as follows:

 Aim:

  • To determine whether the i‐gel, a second‐generation SAD, is superior to tracheal intubation in non-traumatic OHCA in adults, in terms of both clinical and cost effectiveness.

 Objectives:

  1. To estimate the difference in the primary outcome of modified Rankin Scale (mRS) at hospital discharge between groups of patients managed by paramedics randomised to use either the i‐gel or intubation as their initial airway management strategy following OHCA.
  2. To estimate differences in secondary outcome measures relating to airway management, hospital stay and recovery at 3 and 6 months (see section 4.6.2) between groups of patients managed by paramedics randomised to use either the i‐gel or intubation.
  3. To estimate the comparative cost effectiveness of the i‐gel and intubation, including estimating major in hospital resources and subsequent costs (length of stay, days of intensive and high dependency care, etc.) in each group.

The secondary outcomes include initial ventilation success, regurgitation/aspiration, the sequence of airway ventilations delivered and return of spontaneous circulation (ROSC). Additional secondary outcomes will be recorded for patients who survive to hospital and to hospital discharge, including for the latter, Modified Rankin scale and quality of life at 3 and 6 months following OHCA.

It is stated that a 2% improvement in the proportion of patients achieving a good clinical outcome would be clinically significant. This study will also include an economic evaluation. It is estmated that 1,300 paramedics will participate and the cost will be over £2 million.

An Airways-2 web-site is now up and running, and includes an overview of the trial, details regarding the study team and an FAQ page.

Four years may seem a long time to wait and there is always the risk that by the time the results are ready to be published, the landscape of airway management during cardiac arrest has changed. However, it would be difficult to factor out such a risk, and AIRWAYS-2 can be seen as a significant attempt to provide the high level data regarding management of the airway during the initial stages of cardiac arrest we all want to see.

ILCOR, 2015 and the countdown to new guidelines

8704-000_i-gel_resus_mainAs 2014 draws to a close, it seems a good opportunity to look forward to 2015 and consider what the new year may bring. It does look set to be an interesting year. The inaugural European Games will be held in Baku in June, the 7th Rugby World Cup will take place in England in September and Resuscitation 2015 – The Guidelines Congress, will be held in Prague in October!

Sport can be unpredictable, but the winners of the 2015 Rugby World Cup will almost certainly come from one of just five or six nations. I doubt the new 2015 ERC Resuscitation guidelines will provide us with too many surprises either, and neither should they. The ILCOR Scientific Evidence Evaluation and Review System (SEERS) and Consensus on Resuscitation Science and Treatment Recommendations (CoSTR), from which new guidelines are eventually developed, is a process that should ensure the right questions are asked, the relevant evidence is gathered and reviewed and a consensus on the science is obtained before any treatment recommendations are made. New guidelines then follow.

The ILCOR web-site provides the opportunity to review the current status of the PICO questions. In the Advanced Life Support (ALS) section, two questions in particular caught my attention:

Advanced airway placement (ETT v SGA)

Among adults who are in cardiac arrest in any setting  (P), does tracheal tube insertion as first advanced airway  (I), compared with insertion of a supraglottic airway as first advanced airway  (C), change ROSC, CPR parameters, development of aspiration pneumonia, Survival with Favourable neurological/functional outcome at discharge, 30 days, 60 days, 180 days AND/OR 1 year, Survival only at discharge, 30 days, 60 days, 180 days AND/OR 1 year (O)?

Airway placement (Basic vs Advanced)

Among adults who are in cardiac arrest in any setting (P), does insertion of an advanced airway (ETT or supraglottic airway) (I), compared with basic airway (bag mask +/- oropharyngeal airway) (C), change Survival with Favourable neurological/functional outcome at discharge, 30 days, 60 days, 180 days AND/OR 1 year, Survival only at discharge, 30 days, 60 days, 180 days AND/OR 1 year, ROSC, CPR parameters, development of aspiration pneumonia (O)?

Both of the above subjects have been discussed in previous blog posts. The subject of ETT v SGA was covered in a post from October 2012 entitled, ‘Supraglottic airways versus tracheal intubation for OHCA’ and the latter in a post from February 2013 entitled, ‘Pre-hospital airway management for patients with OHCA’.

Since these blog posts were written, additional evidence has been published and it will be interesting to see what conclusions there are from the SEERS/CoSTR process.

In the Basic Life Support (BLS) section, one question stood out as of particular interest:

 Passive ventilation techniques

Among adults and children who are in cardiac arrest in any setting (P), does addition of any passive ventilation technique (eg positioning the body, opening the airway, passive oxygen administration) to chest compression-only CPR (I), compared with just chest compression-only CPR (C), change Survival with Favourable neurological/functional outcome at discharge, 30 days, 60 days, 180 days AND/OR 1 year, Survival only at discharge, 30 days, 60 days, 180 days AND/OR 1 year, ROSC, bystander initiated CPR, oxygenation (O)?

The subject of passive oxygenation has been covered in two blog posts on this site. The first, published in April 2012, asked the question, ‘Should we be passive about oxygenation?’ and the second, in October 2013, entitled, ‘Passive oxygenation – the jury is still out’, concluded that,

‘…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 will be interested to see the conclusions  from the SEERS/CoSTR process on this very interesting subject.

There are many other questions of interest in the ALS and BLS sections, as well as in the Neonatal, Paediatric and Education sections, including use of Impedance Threshold Devices, Induced Hypothermia and Exhaled CO2 detection and esophageal detection devices.

As a big sports fan, I am looking forward to both the European Games and the Rugby World Cup, as well as the Cricket World Cup. However, even these major upcoming sporting events are not anticipated with quite the same excitement as Resuscitation 2015 – The Guidelines Conference! I just can’t wait!

Paediatric Intersurgical i-gel® – a review of the latest evidence

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In a blog post written in December 2012, the question was asked as to whether paediatric Intersurgical i-gel® was an advance over other supraglottic airways? The article reviewed the evidence already published and concluded that:

‘Clinical evidence takes time to build, and some of the studies looked at one size only and all studies have limitations. However, the above evidence suggests i-gel may yet prove to be “a genuine improvement on the pLMA”, as thought possible by White, Cook and Stoddart back in 2009.’

This was a reference to a comment in the excellent review article ‘A critique of elective pediatric supraglottic airway devices’ pubished in Pediatric Anesthesia by White et al, which aimed to present the evidence surrounding the use of currently available supraglottic airways (SADs) in routine paediatric anaesthetic practice. It was also one of the first papers to divide SADs in to first and second generation devices, although the first paper to describe the classification fully was ‘Recent developments in efficacy and safety of supraglottic airway devices’ by Cook and Howes. In the White et al review, first generation devices were described as simple airway tubes, and second generation devices, such as i-gel®, as incorporating ‘specific design features to improve safety by protecting against regurgitation and aspiration’.

The White et al review concluded that ‘The pLMA has yet to be outperformed by any other SAD, making it the premier SAD in children and the benchmark by which newer second generation devices should now be compared’.

Five years on and almost 2 years since my earlier blog post, what additional evidence has been published for the paediatric sizes of Intersurgical i-gel® and does this new data help us to draw a more definitive conclusion to the question I asked back in 2012?

The new data includes two meta-analyses and a number of comparative studies. There are also some interesting letters, review articles and one survey of current UK practice for paediatric SADs. The data ranges from an assessment of the effect of the device on intraocular pressure in paediatric patients who received sevoflurane or desflurane during strabismus surgery to fibreoptic assessment of laryngeal positioning to a clinical evaluation of airway management with the device during MRI examination.

The two meta-analyses were both published in 2014. The first, ‘A systematic review and meta-analysis of the i-gel vs laryngeal mask airway in children’ by Choi et al included nine Randomised Controlled Trials (RCTs) comparing i-gel to different types of laryngeal mask in children. The different types of laryngeal masks were the LMA ProSeal® (pLMA), the LMA Classic® (cLMA), the LMA Supreme® (sLMA) and the Ambu® AuraOnce™ (ALMA).

All four of these devices are quite different in design, and although there is a subgroup analysis for the different types of device, the overall conclusions are a comment on i-gel® in comparison to all the laryngeal masks as a collective group. The conclusions were that, ‘i-gel was similar to LMAs when used in children and delivered ventilation pressures 3cm H20 higher than LMAs. Few complications were reported with either airway.’

The other meta-analysis, ‘Evaluation of i-gel airway in children: a meta analysis’, by Maitra et al and published in Pediatric Anesthesia, included nine RCTs where i-gel® had been compared to the cLMA and/or the pLMA . The authors concluded that ‘The i-gel® airway is at least equally effective with laryngeal mask airway ProSeal and laryngeal mask airway Classic and provides a significantly higher oropharyngeal leak pressure than both the laryngeal masks.’ The authors of both meta-analyses acknowledge a number of limitations to their papers. An important consideration is certainly whether any statistically significant differences identified between devices are also clinically significant. i-gel

A particularly interesting article, published in 2013, is ‘Current practice of pediatric supraglottic airway devices – a survey of members of the Association of Paediatric Anaesthetists of Great Britain and Ireland (APAGBI)’. It assessed usage of SADs in routine and difficult airways in the UK by distributing a survey with sixteen questions to all UK members of the APAGBI. Two hundred and fourty-four members replied.

88% ‘favoured’ first generation SADs for routine use and 85% ‘preferentially’ for use in the failed intubation scenario. As the pLMA, a second generation device, is often considered the premier SAD for use in children, this is perhaps a little surprising. In fact, only 1% of responders confirmed the pLMA as their first choice/usual SAD. 49% would never use a SAD on a patient weighing less than 5kg. Only 15% ‘felt that an esophageal drainage tube was an important feature.’

The authors confirm that, ‘Fibreoptic guided intubation via an SAD is used electively by 46% of respondents, and only 3% regularly employ this technique. 17% have used the technique in an emergency, 20% have only practiced it on a manikin, and 9% have never used or seen this technique in any situation.’

With regard to i-gel, 37% of respondents reported they had access to the device. This compared to 25% with access to the pLMA and 14% to the sLMA. However, only 1% confirmed i-gel® as their first choice/usual SAD. The same percentage as reported for the pLMA. 87% had access to a classically shaped laryngeal mask airway, with 77% using it as their first-choice/usual SAD. Only 15% considered an esophageal drain channel as an important design feature.

So why the low use and apparent limited interest in second generation SADs, such as i-gel® and the pLMA amongst members of the APAGBI? The authors suggest there may be a number of reasons for the slower adoption than with the adult sizes, such as paediatric sizes coming onto the market later than adult sizes, the bulkier design of paediatric sizes and because aspiration associated with SAD use is seen less frequently and has less morbidity in children when compared with adults. It maybe the potential safety features are therefore considered by paediatric anaesthetists to be less essential.

The authors conclude that, ‘Research currently has little influence over the choice of which SAD to use, which is more likely determined by personal choice and departmental preference.’

Whilst writing this review, two additional papers of interest were published in Anaesthesia. The first, ‘A performance comparison of the paediatric i-gel with other supraglottic airway devices’ by Smith & Bailey includes data from fourteen RCTs and eight observational studies. The authors conclude that, ‘the i-gel is at least equivalent to other supraglottic airway devices curently available for use in children, and may enable a higher oropharyngeal leak pressure and an improved fibreoptic view of the glottis.’

The other paper is a particularly interesting editorial, entitled, ‘Which supraglottic airway will serve my patient best?, also published in Anaesthesia. Whilst not specifically focussed on paediatric SADs, the paper mentions two of the meta-analyses discussed in this blog post.

The authors Kristensen, Teoh and Asai consider how the ‘right’ device should be chosen, when a new device can be introduced into clinical practice, the role of manikin studies and manufacturer’s responsibilities. They also discuss the ADEPT guidance formulated by the Difficult Airway Society (DAS).

The authors comment that, ‘Until significantly better features of a new airway device relating to clinically important outcome measures have been shown, we should be cautious about replacing the conventional device with a new one…We can judge whether or not a new device has a clinically meaningful difference (superiority) to the conventional device, mainly by assessing the results of randomised controlled studies and meta-analyses. Nevertheless, if randomised controlled studies only show statistically significant differences that are not clinically meaningful, the reports of meta-analyses will not provide clinically meaningful information for our decision making.’

So what conclusions can we draw from the new data published for i-gel? Is the device superior to other paediatric supraglottic airways already available? Well, the new data is varied in subject matter, includes a number of RCTs, comparative studies and meta-analyses. Most of the data is encouraging and some possible advantages have been identified. However, there are always areas where more data is required or desirable. I will leave you to review the evidence for yourself and draw your own conclusions.

Note:
i-gel is a registered trademark of Intersurgical Ltd. LMA Classic, LMA ProSeal, LMA Unique and LMA Supreme are registered trade marks of the Laryngeal Mask Company Ltd. cLMA, pLMA, and sLMA are abbreviations used in some journal articles. They refer to the LMA Classic, LMA Proseal and LMA Supreme respectively. Ambu is a registered trademark of Ambu A/S.

Pre-hospital airway management – the debate continues

 In a recent editorial published in Resuscitation, entitled ‘Pre-hospital airway management: The data grows rapidly but controversy remains’, David Lockey and Hans Morten Lossius discuss the results from three studies published in the same issue:

1. An update of out of hospital airway management practices in the United States.

2. Higher insertion success with the i-gel supraglottic airway in out-of-hospital cardiac arrest: A randomised controlled trial.

3. The impact of airway management on quality of cardiopulmonary resuscitation: an observational study in patients during cardiac arrest.

An update of out of hospital airway management practices in the United States

Digges et al utilised the 2012 National Emergency Medical Services Information System (NEMSIS) Public-Release Research Data Set to examine over 19 million EMS activations. This included 74,993 intubations, 21,990 alternate airway patient care events (confirmed as either a Combitube®, Esophageal Obturator, Laryngeal Mask Airway or King LT®) and 1,332 Cricothyroidotomys. BVM ventilation was undertaken on 56,025 occassions and there were 54,241 oropharyngeal airway (OPA) and 404,828 nasopharyngeal airway (NPA) interventions.

Overall intubation success was 85.3%. Alternate airway success rates were 79.6% overall. The most successful of these was was the King LT® (89.7%) and the least successful the Esophageal Obturator (38.0%).

It is interesting to make some comparison of these results to an earlier examination of the same database for EMS activations four years earlier in 2008. The earlier study included fewer states, so any comparison must be undertaken with caution, but the alternate airway devices recorded as having been used were the same in both reports.

This is worth noting, as the alternate airway devices used are quite different from those used in some other markets such as the UK. As reported in a previous blog post, in the Adult ALS chapter of the Resuscitation Council (UK) 2010 Resuscitation Guidelines, it is confirmed that ‘The Combitube® is rarely, if ever, used in the UK and is no longer included in these guidelines’, and in addition that the Laryngeal Tube (LT) ‘is not in common use in the UK’. What about the rest of Europe? In the 2010 European Resuscitation Council (ERC) Guidelines for Resuscitation, it is stated that ‘Use of the Combitube® is waning and in many parts of the world is being replaced by other devices such as the LT’. In the two papers utilising the NEMSIS data discussed in this blog post, there is no mention of the newer 2nd generation SADs such as the i-gel® and LMA Supreme® which are in regular use in many countries.

In an editorial published in 2009 in Resuscitation, the official journal of the European Resuscitation Council, entitled, ‘Airway management for out-of-hospital cardiac arrest – More data required’, Nolan and Lockey concluded that ‘New airway devices appear frequently but, in our opinion, the three currently available disposable SADs that need to be studied for use during CPR are the i-gel®, the LMA Supreme® and the disposable LT’. Only one of these devices, the LT, was used in the Diggs update of out-of-hospital airway management practices in the United States.

This is significant, as the authors of the update of out of hospital airway management practices in the U.S. state that, ‘This study and many others show that there are problems with out-of-hospital ETI. The results of this study show that alternate airways are not the answer’. As Lockey and Lossius comment, the latter point is a ‘strong and controversial statement’. The latter also make a number of additional important points, including confirmation that ‘although supraglottic devices are clearly not all equal, the highest performing devices have similar success to intubation without the high training burden and risks of oesophageal intubation’.

This leads in nicely to the second study discussed in their editorial:

Higher insertion success with the i-gel® supraglottic airway in out-of-hospital cardiac arrest: A randomised controlled trial.

 Lockey and Lossius introduce the study as follows:

‘Confirming the major difference between the performance of different supraglottic devices, and also published in this issue, is a pre-hospital randomised trial of the second generation i-gel™ device vs an LMA™. Significantly different success rates were demonstrated and the second generation device clearly outperformed the LMA™.’ The laryngeal mask compared to i-gel® in this study was the Portex® Soft Seal® device.

A first generation SAD has been described as a ‘simple airway tube’ and a second generation SAD as ‘incorporating specific design features to improve safety by protecting against regurgitation and aspiration’ (White, Cook and Stoddart)

The paper Lockey and Lossius refer to is a single centre, prospective parallel-group ‘open label’ randomised controlled trial (RCT) in which patients in cardiac arrest were allocated to either the Intersurgical i-gel® supraglottic airway or the Portex® Soft Seal® Laryngeal Mask. The primary outcome was successful insertion as determined by the paramedic who inserted the device.

Fifty-one patients were randomised. Three were not in cardiac arrest, so the final analysis reports on data from forty-eight patients. The Intersurgical i-gel® had an insertion success rate of 90% (18/20) compared to 57% (16/28) with the Portex® Soft Seal® (p=0.023). The authors concluded that:

‘The i-gel® supraglottic airway was associated with higher successful insertion rates in subjects with out-of-hospital cardiac arrest. The i-gel® supraglottic appears easier for paramedics to use and appears a suitable first line supraglottic airway for out-of-hospital cardiac arrest’.

As confirmed earlier, there was no data for i-gel® or a number of the other newer 2nd generation supraglotic airways in ‘An update of out of hospital airway management practices in the United States’ by Diggs et al. Evidence for one supraglottic airway should not be extrapolated to another device with different design characteristics, so their data is only relevant to those devices included.

The impact of airway management on quality of cardiopulmonary resuscitation: an observational study in patients during cardiac arrest

The third paper discussed by Lockey and Lossius is, ‘ The impact of airway management on quality of cardiopulmonary resuscitation: an observational study in patients during cardiac arrest’. This prospective observational study by Yeung et al enrolled 100 consecutive patients between 2008 and 2011 with the aim of determining the effect of advanced airway use, either an endotracheal tube (ET) or laryngeal mask airway (LMA) on the no flow ratio (NFR) and other measures of CPR quality. The control cohort was patients receiving only bag-mask ventilation. The results showed use of an advanced airway during in-hospital cardiac arrest was associated with improved no flow ratios. The primary reason for the improvement appears to be switching from a compression to ventilation ratio of 30:2 to continuous chest compressions and asynchronous ventilation. Further details can be accessed with the earlier link.

A particularly interesting aspect of this paper is the discussion section, where the uncertainties about the role of advanced airways in cardiac arrest are examined. Firstly there is uncertainty about whether ventilation is required at all in the early stages of cardiac arrest (the Yeung et al paper examined patients in the later stage of out-of-hospital or in-hospital cardiac arrest where some form of ventilation is required). They mention the studies from Arizona prioritising Cardio-Cerebral Resuscitation (CCR) over ventilation in the early stages of cardiac arrest.

The timing of airway intervention and any impact on interruptions in chest compressions are also likely to be important. There is discussion regarding interruptions in CPR and the link to reductions in coronary perfusion pressure and development of ventricular fibrillation (VF). The potential impact of supraglottic airways on carotid blood flow, dislodgement of LMAs and aspiration risk are also discussed. All important subjects.

In their editorial, Lockey and Lossius comment that, ‘This study is one of several that demonstrate potential improvements in quality indicators in resuscitation which may be in conflict with large studies with undifferentiated casemix and resuscitation techniques which generally question the value of advanced life support techniques in cardiac arrest or trauma patients.’

Conclusion

So where does all this new data leave us? Lockey and Lossius conclude that ‘Our interpretation of the currently available data on pre-hospital advanced airway management is that the risks and benefits need to be considered for every patient on scene with airway compromise. The management that results from this analysis will depend on the indications and condition of the patient as well as the skills and available interventions on scene.’ This is not entirely dissimilar to the statement in the European Resuscitation Council (ERC) guidelines for resuscitation 2010 in relation to airway management during cardiac arrest, which state that ‘There are no data supporting the routine use of any specific approach to airway management during cardiac arrest. The best technique is dependent on the precise circumstances of the cardiac arrest and the competence of the rescuer.’

With regard to SADs, Lockey and Lossius conclude:

‘The constant evolution of existing supraglottic airways and the introduction of new devices makes generalisation and performance assessment of these devices difficult, but the expanding dataset will hopefully ensure that only the highly performing devices will be used in future studies, thus making interpretation more straightforward’.

No doubt REVIVE#2 will provide some useful additional data in this regard and it is to be hoped that additional randomised controlled trials, similar to the study published by Middleton et al discussed here, will be conducted so the dataset continues to expand.

Arthur Guedel and the oropharyngeal airway

One-piece Guedel

Any definitive history of the development of the oropharyngeal airway (OPA) is likely to include reference to Arthur Guedel and the OPA he described in a short article entitled, ‘A nontraumatic pharyngeal airway’ published in the Journal of the American Medical Association (JAMA) in 1933. In little more than a dozen lines he described a device which today is almost synonymous with the term oropharyngeal airway.

Although Joseph Thomas Clover (1825-1882) is credited with first use of an artificial airway, as this was a nasopharnygeal device, it is Sir Frederic William Hewitt (1857-1916) who is usually acknowledged as being first to describe the use of an oropharyngeal airway, in an article entitled ‘An artificial air-way for use during anaesthetisation’, published in The Lancet in 1908.

Hewitt was appointed as anaesthetist to King Edward VII in 1901. He was also a founding member of the Society of Anaesthetists in London and was made a member of the Royal Victorian Order (4th class) in 1902 for personal service to the King. The Frederick Hewitt Lecture was inaugurated by the Royal College of Surgeons (now the Royal College of Anaesthetists), in 1950. Fittingly, the lecture is now given biennially with the Joseph Clover Lecture – two pioneers of airway management appropriately acknowledged for their contribution to anaesthesia and airway management. The names of those anaesthetists who have delivered a Hewitt or Clover lecture reads like a roll call of anaesthetic icons, and includes Sir Ivan Magill, Sir Robert Macintosh, Gordon Jackson Rees and Brian Sellick.

Hewitt and the airway he designed are discussed in a historical note published in Anaesthesia by RP Haridas entitled, ‘The Hewitt airway – the first known artificial oral ‘air-way’ 101 years since its description’. The original airway incorporated a straight rubber tube, but a curved version was later developed. Brimacombe described the Hewitt airway as the forerunner to many modern oropharyngeal airways (Laryngeal Mask Anesthesia. Principles & Practice. Elsevier Ltd. 2nd edition. 2005).

Hewitt was undoubtedly an anaesthetic giant of the late nineteenth and early twentieth century, yet his contribution to anaesthesia and airway management may be less immediately well known than that of Arthur Guedel.

Maltby confirms in ‘Notable Names in Anaesthesia’ that Arthur Guedel was born in Cambridge City, Indiana in 1883. Despite losing three fingers when he was a teenager, Guedel still managed to become an accomplished pianist and composer! His medical career started at the Medical College of Indiana in 1903. After graduating in 1908, he was interned at the City Hospital in Indianapolis where he was required to administer ether and chloroform. He eventually served as an anaesthetist in the American Expeditionary Forces in France in World War One, where the challenges faced by inexperienced personnel from the army medical corps provided the impetus to develop a classification of the stages of anaesthesia.

Guedel also created the first inflatable cuffs for ET tubes, experimenting with location, above, below or at the vocal cords, cuff pressures and possible inflation techniques. Around this time, Guedel would often use his own pet dog, appropriately named ‘Airway’, as part of his lecture demonstrations. Maltby confirms that Airway survived to enjoy ‘an honourable retirement with the Waters family in Madison, Wisconsin.’ A glance at the content of Guedel’s lecture demonstrations from the 1920s suggests that Airway’s survival to retirement was by no means a foregone conclusion and can itself be considered an achievement.

The recipient of the dog, Ralph Waters, wrote a personal tribute to his friend Arthur Guedel in the BJA in 1953 as part of the ‘Eminent Anaesthetists’ series. He confirmed that the saying, ‘If a man loves dogs he will love mankind’ was true of Guedel. He discusses their correspondence, at its most prolific between 1925 to 1945, his athleticism, and his motto for many years, ‘Maintain Flying Speed’, taken from the pilot of the time whose altitude began to fail as his forward progress diminished. Interestingly, he makes no mention of the oropharyngeal airway for which Guedel is perhaps most often remembered today.

Guedel originally described his oropharyngeal airway in JAMA as follows: ‘The airway herewith depicted is made of rubber and is sufficiently soft and flexible not to traumatize yet amply rigid to maintain an open oropharyngeal air passage under all conditions.’ He also confirmed that ‘the metal insert extends into the airway for about 2cm from the oral opening and prevents collapse of the rubber between the teeth’.

Thomas Baskett, in his 2004 article on Guedel published in Resuscitation, quoted Guedel’s own 1937 publication, ‘Inhalational Anesthesia: A Fundamental Guide’, describing use of the oropharyngeal airway during anaesthesia when ‘there is sufficient muscular relaxation to permit the lower jaw to fall backward allowing the base of the tongue to lie against the posterior wall of the pharynx. Depending upon the anatomical structure of the pharynx, this may partially or completely obstruct inspiration. It is usually remedied at once by the insertion of a pharyngeal airway which will hold the tongue forward from the pharyngeal wall.’

Dorsch and Dorsch in ‘Understanding Anesthesia Equipment (5th edition)’, describe an oropharyngeal airway as follows ‘…..may be made of elastomeric material or plastic. It has a flange at the buccal end to prevent it from moving deeper into the mouth. The flange may also serve as a means to fix the airway in place. The bite portion is straight and fits between the teeth or gums. It must be firm enough that the patient cannot close the lumen by biting. The curved portion extends backward to correspond to the shape of the tongue and palate.’

The International Standard ISO 5364: 2008 ‘Anaesthetic and respiratory equipment – oropharyngeal airways’ describes an oropharyngeal airway as a ‘device intended to maintain a gas pathway through the oral cavity and pharynx’. It confirms the size should be designated by the nominal length expressed in centimetres and provides a table to show how the length should be calculated. A table is provided confirming designated size (nominal length) , as well as tolerances and minimum inside dimensions. The latter is relevant to the ability to pass other devices, such as a suction catheter, through the airway.

The European Resuscitation Council (ERC) Guidelines for Resuscitation 2010 confirm that ‘An estimate of the size required is obtained by selecting an airway with a length corresponding to the vertical distance between the patient’s incisors and the angle of the jaw.’

The original Guedel airway was made of rubber with a metal insert. Most modern Guedel airways are made of plastic. Dorsch and Dorsch confirm that modifications to aid flexible fibreoptic intubation have been described and Guedel airways with the bite block incorporated into one moulding, thereby eliminating the danger of loose or detached bite blocks, are also available.

The Guedel airway has endured the test of time and remains one of most widely known and used airway adjuncts eighty years after it was first described. It is of simple design, but many of the best inventions often are.

 

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?