Airway management in a combat zone

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

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

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

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

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

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

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

The conclusions of the report include the following:

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

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

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

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

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

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

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

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.

Paediatric Intersurgical i-gel® – is it an advance over other SADs?

In 2009, Pediatric Anesthesia published a paper by White, Cook and Stoddart, entitled, ‘A critique of elective pediatric supraglottic airway devices’, which aimed to present the evidence surrounding the use of currently available supraglottic airways (SADs) in routine anaesthetic practice. It was one of the first papers to divide SADs in to first and second generation devices. 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 review highlighted that, apart from the LMA Classic® (cLMA) and LMA Proseal® (pLMA), there was a lack of high quality data of efficacy for SADs, stating that, ‘The best evidence requires a randomized controlled trial comparing a new device against an established alternative, properly powered to detect clinically relevant differences in clinically important outcomes. Such studies in children are rare. Safety data is even harder to establish, particularly for rare events such as aspiration’.

Whilst the authors did comment on the i-gel, at the time of their review paediatric sizes of the device were not available. However, they did note the i-gel offers, ‘the possibility of a genuine improvement on the pLMA’, based on the stability provided in adult sizes by the elliptoid shape of the device, but that it remained to be seen whether this stability would be retained in the paediatric sizes. The 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’.

(fig 1)

Paediatric sizes of i-gel (fig 1) became available in the latter half of 2009, extending the lower weight range from 30kg to 2kg. As with the adult sizes, the paediatric sizes have a non-inflatable cuff, a gastric channel (except size 1), an integral bite block and a buccal cavity stabiliser. Details of the applicable weight range for each size are shown below (fig 2).

(fig 2)

The first independent data on the use of the new paediatric sizes came from the Hautepierre University Hospital of Strasbourg, who presented an abstract on the device at the SFAR Congress in Paris in September 2009 and at the Amercian Society of Anesthesiologists (ASA) Annual Meeting in October 2009, entitled, ‘The i-gel in paediatric surgery: Initial series’. This abstract reported on 50 insertions of the device in patients between 6 months and 14 years. Stability of the device and avoidance of intubation were seen as advantages. An interview with Professor Pierre Diemunsch, Consultant at the Hautepierre University Hospital, discussing their findings is available on YouTube.

A number of observational/cohort studies followed. Beringer et al studied the i-gel in 120 anaesthetised patients to assess efficacy and usability. First time insertion success was 92%, overall insertion success was 99% and the median leak (seal) pressure was 20cm H2O. One child regurgitated without aspirating. 16 manipulations were required in 11 children to improve the airway. The authors concluded that, ‘other complications and side effects were infrequent. The i-gel was inserted without complications, establishing a clear airway and enabling spontaneous and controlled ventilation in 113 (94%) children.’

Hughes et al studied the device in 154 children. First time insertion success was 93.5%, overall insertion success was 99.3%. The median leak (seal) pressure was 20cm H2O. The authors concluded that i-gel provided a satisfactory airway during anesthesia for spontaneously breathing infants and children, but felt that to ensure a clear airway, considerable vigilance is required when fixing the device in the mouth.

Fixation is important. The instructions for use for the paediatric i-gel make it clear that as soon as insertion has been successfully completed, the i-gel should be held in place until and whilst the device is secured in place with tape maxilla to maxilla.

Randomised comparative studies followed. The first by Theiler et al, compared i-gel to the Ambu® AuraOnce. This was followed by comparisons to the cLMA . Lee et al found a similar leak pressure between i-gel and the cLMA, but a shorter insertion time for i-gel – 17 secs median (IQR 13.8 – 20.0) v 21.0 secs median (IQR 17.5 – 25.0) and an improved glottic view.

A summary of seal pressures from published clinical studies for the paediatric sizes of i-gel is shown below (fig 3)

(fig 3 ) Paediatric i-gel seal pressures

Considering the conclusion made by White, Cook and Stoddart, perhaps the most interesting comparisons are those to the pLMA.

Two such comparative studies have so far been published. The first was a randomised prospective study entitled, ‘Comparison of size 2 i-gel supraglottic airway with LMA-ProSeal and LMA-Classic in spontaneously breathing children undergoing elective surgery’, which compared the devices in 120 children aged 2-5 years scheduled for surgery of <1 hour duration. The oropharyngeal seal pressure for i-gel was higher than both the cLMA and the pLMA: 26, 22 and 23 cmH20 respectively. First time insertion success was also higher for the i-gel than both the cLMA and the pLMA, 95%, 90% and 90% respectively. The authors concluded that ‘Pediatric size 2 i-gel is easy to insert and provides higher OSP compared with the same size pLMA and cLMA in spontaneously breathing children undergoing elective surgery. It may be a safe alternative to LMA in day care surgeries.

In November 2012, Acta Anaesthesiologica Scandinavica, published a crossover design study by Gasteiger, Brimacombe, Oswald, Perkhofer, Tonin, Keller and Tiefenthaler, entitled ‘LMA ProSeal® vs i-gel in ventilated children: a randomised, crossover study using the size 2 mask‘. The paper studied fifty one children aged 1.5 – 6 years. Leak pressure for both devices was similar, as was fibreoptic position, with the vocal cords visible from the distal airway tube in 94% and 96% respectively. The authors concluded that ‘oropharyngeal leak pressure and fibreoptic position of the airway tube are similar for the size 2 LMA ProSeal® and i-gel in non-paralysed ventilated children’

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.

Interestingly, a number of other studies on paediatric i-gel have recently been published, including, ‘A randomised equivalence trial comparing the i-gel and the laryngeal mask airway Supreme in children‘, in which i-gel had a higher seal pressure than the sLMA, 20 (IQR 18-25) v 17 (14-22) cm H20 respectively.

‘A comparison of three supraglottic airway devices used by healthcare professionals during paediatric resuscitation simulation‘ compared the i-gel to the Laryngeal Tube (LTS) and the LMA Unique® (uLMA) in manikins. A total of 66 healthcare providers, 22 paramedics, 22 nurse anaesthetists and 22 anaesthesia residents participated in the study. The authors concluded that ‘In terms of both the time required for successful placement and the rate of successful placement, the i-gel is superior to the laryngeal mask and tube in paediatric resuscitation simulations by healthcare workers with different levels of experience with paediatric airway management‘.

More data is awaited.

Note:
i-gel is a registered trademark of Intersurgical Ltd.

Classification of supraglottic airways

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

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

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

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

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

• Cuffed oropharyngeal airway, where the ventilatory opening is located at the base of the tongue and a sealing surface is located in the oropharynx.

• Laryngeal masks, where the ventilatory opening is surrounded by the cuff, which forms a seal with the periglottic tissues. The ventilatory opening and the cuff seal usually represent the most distal portion of the device.

• Pharyngeal or pharyngeal-esophageal tube, where a cuff surrounds the ventilatory tube in a circumferential fashion and is located proximal to the ventilatory opening. This design compartmentalizes the pharynx, with the cuff serving as a sealing divider between the proximal and distal pharyngeal compartments, and the ventilatory opening(s) are located in the distal pharyngeal compartment.

• Pharyngeal airway liner, which is represented by the streamlined liner pharyngeal airway (SLIPA^TM). This is a shell-like device that, upon insertion, expands the soft tissues of the neck. The tension of the elastic neck soft tissues that surround the device provides the sealing mechanism. The ventilatory opening is located within the shell in the periglottic area.

• Device with a soft, gel-like, non-inflatable cuff and widened, concaved buccal cavity stabiliser. The sealing mechanism is created by the soft non-inflatable cuff accurately mirroring the anatomy of the laryngeal inlet to create an impression fit, without the need for cuff inflation.

 This classification did little to reduce complexity.

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

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

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

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

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

Fig 1

Fig 2 – Infographic

Supraglottic airways versus tracheal intubation for OHCA

Whilst the 2010 European Resusciation Council (ERC) guidelines confirm ‘There is insufficient evidence to support or refute the use of any specific technique to maintain an airway and provide ventilation in adults with cardiopulmonary arrest.’ They go on to confirm that despite this ‘tracheal intubation is perceived as the optimal method of providing and maintaining a clear and secure airway.’ However, they also point out that without adequate training and experience, the incidence of complications with tracheal intubation can be unacceptably high.

As a result, in some countries, such as the UK, there has been a general move towards the use of supraglottic airway devices in the pre-hospital setting. This has been supported by the Joint Royal Colleges Ambulance Liaison Committee (JRCALC) Airway Working Group, who in 2008 published ‘A Critical Reassessment of Ambulance Service Airway Management in Pre-Hospital Care’, which recommended that ‘The majority of those managing patients’ airways in the pre-hospital setting should be trained to insert a supraglottic airway device instead of a tracheal tube’. The College of Paramedics outlined a number of concerns and reservations with this approach, but despite this, the use of supraglottic airways for OHCA has increased in the UK.

It was therefore interesting to read the recent clinical study published in Resuscitation, entitled ‘Endotracheal intubation versus supraglottic airway insertion in out-of-hospital cardiac arrest’, by Wang et al. The study is a secondary analysis of data from the multi-centre ‘Resuscitation Outcomes Consortium (ROC) PRIMED trial, looking at adult non-traumatic out-of-hospital cardiac arrest (OHCA) receiving successful supraglottic airway (SGA) insertion of the King Laryngeal TubeTM, Combitube®, and Laryngeal Mask Airway, or successful intubation with an endotracheal tube (ETI). It included 10,455 adult OHCA. 8,487 of these received ETI and 1,968 an SGA. The survival to hospital discharge was 4.7% for ETI and 3.9% for SGA.

The results are interesting, but as the authors themselves acknowledge, there are limitations and confounders, including the order of airway device insertion, and the number and duration of insertion attempts. The data was not intended for primary evaluation of airway management techniques, and information regarding interruptions to compressions during insertion of the airway device, ventilation rates or tidal volumes could not be accounted for or was not regarded as reliable. Despite this, the results from this paper are certainly worth further consideration and it is likely will be the subject of significant discussion amongst the Emergency Medicine fraternity and beyond.

Of course, the absolute difference in survival rates in this study was small, and whilst confirming that observational data are clearly of value, an editorial published in the same issue of Resuscitation as this study, ‘ROC, paper, scissors: Tracheal intubation or supraglottic airway for OHCA?’ pointed out that ‘randomised trials are still widely considered to be the gold standard for addressing focused clinical questions’. Indeed, Wang et al themselves confirmed that ‘prospective randomised assignment may represent an optimal strategy for comparing OHCA outcomes between ETI and SGA’.

As reported in an earlier blog post, a randomised trial comparing two SGAs (LMA Supreme® and i-gel®) to ‘current practice’ which it is believed will usually be ETI, is underway in the UK, called the ‘Airway Management Feasibility Study (REVIVE – Airways)’. It is also interesting to note that neither of the two SGAs in the REVIVE study were included in the US study being discussed here. Clearly, results for one SGA cannot be extrapolated to another, so these results are only relevant for the devices studied. Given the considerable differences in design and performance characteristics between the CombiTube®, King Laryngeal TubeTM, standard Laryngeal Mask Airway and the LMA Supreme® and i-gel®, it is possible, perhaps likely, results for the latter two devices would have been quite different.

Whilst we await the results of high quality randomised controlled trials of the use of SGAs for CPR, the conclusion given in the study by Wang et al seems entirely reasonable ‘EMS medical directors must consider patient characteristics, device efficacy and practitioner skill and training when selecting OHCA airway management strategies.’ This approach is echoed by the ERC in their 2010 guidelines ‘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’. Now you can’t really argue with that.