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.

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.

 

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.

The i-gel SGA for prehospital airway management in a UK ambulance service

As previously reported on this blog page, the optimum method for management of the airway during cardiac arrest (CA) continues to be the subject of lively debate. The European Resuscitation Council (ERC) guidelines confirm 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 the use of supraglottic airways (SADs) for CA, the call went out in an editorial entitled ‘Airway Management for out-of-hospital cardiac arrest – more data required’, published in 2009 in Resuscitation by Nolan and Lockey for high quality randomised controlled trials (RCTs) of the use of SADs for cardiopulmonary resuscitation (CPR). The REVIVE airways study process is an attempt to provide just such evidence by conducting a randomised comparison of the ventilation success of two 2nd generation supraglottic airways, i-gel® and the LMA Supreme®, in the initial airway management of OHCA compared to current practice, which is expected to be tracheal intubation. The REVIVE team published an initial report in the BMJ on the feasibility of such a study protocol earlier this year. A full trial is expected to follow.

In the meantime, healthcare professionals are still faced with the dilemma of which airway device to use for CPR, so any new data or evidence in this area, even if it is not high level, is likely to be of interest.

Duckett et al have just published the results of two retrospective clinical audits in the Emergency Medicine Journal, reviewing the use of basic and advanced airway management techniques within the UK North East Ambulance Service NHS Foundation Trust (NEAS) for cardiac arrests, entitled, ‘Introduction of the i-gel supraglottic airway device for prehospital airway management in a UK ambulance service.’

The audit confirmed that a range of basic and advanced airway management techniques are being successfully used to manage the airways of CA patients in NEAS and that i-gel is emerging as a popular choice for maintaining and securing the airway during pre-hospital CPR.

The success rates for i-gel insertion at 94% and 92% were higher than for the endotracheal tube (ETT) at 90% and 86%. In determining these results, the Quality Improvement Officer audited whether the technique used had been documented by the crew as ‘successful’ or ‘unsuccessful’, but no further details are provided in this report as to how success or failure was determined. Any additional relevant documentation which may indicate problems such as regurgitation, aspiration or trauma provided by the paramedic and/or the receiving A&E department were also considered. The abstract reports that ‘The re-audit indicated an upward trend in the popularity of i-gel; insertion is faster with a higher success rate, which allows the crew to progress with the other resuscitation measures more promptly.’

In light of this new data, it is interesting to note that an addition to the i-gel product range, specially designed for use during resuscitation, is also now available. The i-gel O2 Resus Pack (figure 1) contains a modified i-gel with a supplementary oxygen port.

figure 1

figure 1

It also includes a sachet of lubricant for quick and easy lubrication of the i-gel O2 prior to insertion, an airway support strap to secure the i-gel O2 in position and a suction tube for insertion through the gastric channel to empty the stomach contents (figure 2)

figure 2

figure 2

The i-gel O2 has been designed to facilitate ventilation as part of standard resuscitation protocols such as those designated by the ERC.

However, the i-gel O2 incorporates a supplementary oxygen port, permitting use for the delivery of passive oxygenation or Passive Airway Management (PAM), as part of an appropriate CardioCerebral Resuscitation (CCR) protocol. The use of passive oxygenation is discussed in an earlier blog post, Should we be passive about oxygenation?

Pre-hospital airway management for patients with OHCA

An interesting study was published in the January 2013 issue of The Journal of the American Medical Association (JAMA), by Hasegawa et al from Japan, entitled, ‘Association of Prehospital Advanced Airway Management with Neurologic Outcome and Survival in Patients with Out-of-Hospital Cardiac Arrest’. This prospective, nationwide population based study examined data from over 649,000 adult patients in Japan who had an OHCA in whom resuscitation was attempted by emergency responders from January 2005 to December 2010.

The study was designed to test the hypothesis that prehospital advanced airway management (AAM) is associated with favourable outcome after OHCA. Advanced airway management (AAM) is defined as Endotracheal Intubation (ETT) or use of a supraglottic airway (SAD). AAM was compared to conventional bag-mask-valve (BVM) ventilation for neurologically favourable survival. The results for each group were as follows:

Endotracheal Intubation 1.0% (95%CI, 0.9% – 1.1%)
Supraglottic Airway 1.1% (95% CI, 1.1% – 1.2%)
Bag-valve-mask 2.9% (95% CI, 2.9% – 3.0%)

Return of spontaneous circulation (ROSC) and one-month survival were also assessed.

The results of this study show that among adult patients with OHCA CPR, any type of AAM (ETT and/or SAD) is associated with decreased odds of neurologically favourable survival compared with conventional BVM ventilation. The authors conclude that their observations, ‘contradict the assumption that aggressive airway intervention is associated with improved outcomes and provide an opportunity to reconsider the approach to prehospital airway management in this population’. Of course, Hasegawa et al are also careful to confirm their study has several limitations, and outline each in detail.

In an editorial in the same issue of JAMA, ‘Managing the Airway During Cardiac Arrest’, Wang and Yealy provide context for this study by discussing the reservations and potential limitations of use of a BVM during OHCA and the reasons why use of more advanced airways has been prioritised in most emergency medical services systems in North America. They also discuss the questions that have been raised regarding the wisdom of the wide use of ETT out-of-hospital. They conclude that although this study from Japan is not the first report to suggest higher survival rates with BVM ventilation, ‘the study is large, methodologically rigorous and compelling’.

In recent years, the discussion regarding the optimal technique for airway management during OHCA has generally focused on the use of SADs versus ETT, so this study certainly broadens the debate. What interested me when reading this paper was the three SADs listed as being permitted for use from 1991 onwards by emergency life-saving technicians in Japan. These were The Laryngeal Mask Airway, Laryngeal Tube and Oesophageal-Tracheal Twin Lumen Device (Combitube®). It is not entirely clear to me whether these three devices were simply referenced as examples of SADs, or whether these were the only SADs used. I presume the latter. It is a point of interest, as each of these SADs have quite different design and performance characteristics, as do other more recently developed devices, so it is quite possible that if the results for each SAD had been included individually as well as collectively, a difference in outcome between them may have been evident, and this would have been interesting to reference in the results.

Interestingly, in a study published last year in Resuscitation by Wang et al, entitled, ‘Endotracheal intubation versus supraglottic airway insertion in out-of-hospital cardiac arrest’, among the 1968 SADs used, the type of device reported for 1444 cases included 909 (63%) Laryngeal Tube, 296 (20.5%) Combitube® and 239 (16.6%) Laryngeal Mask Airway. Exactly the same three devices listed in the Japanese study.

In the UK, the picture is quite different. In the 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’. So of the three devices referred to in both the study from Japan and the study last year from Wang regarding North America, only one of them, the Laryngeal Mask Airway, is in common use.

As for second generation devices in the UK, such as the Intersurgical i-gel®, these are increasingly being considered and used for OHCA. Second generation SADs can be defined as a device that ‘incorporates specific design features to improve safety by protecting against regurgitation and aspiration’. This improved safety is usually provided by the incorporation of a gastric channel or drain tube. In addition, second generation SADs usually provide higher seal pressures than first generation devices and often incorporate an integral bite block (see my earlier blog post on November 12 regarding the classification of supraglottic airways for more details). 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 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 two studies referred to here from Japan and North America.

So what might we conclude from this? Well, firstly there appears to be a significant difference between the types of SAD in common use for OHCA in Japan and North America to the SADs in common use for OHCA in the UK and Europe. Secondly, that we should be cautious when considering the results and clinical relevance of data provided for a group of SADs, if the data for the individual devices as a sub-set is also not available. Finally, and perhaps most importantly, that we should resist the temptation to extrapolate the results for one type of SAD to another with quite different design characteristics. All supraglottic airways are not the same. No doubt the debate about the optimal technique to maintain an airway and provide ventilation during OHCA will continue.