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.

Passive oxygenation – the jury is still out

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Use of SADs in the prehospital setting – a new review

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

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

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

In anaesthesia circles in particular, a new classification of SADs into 1st and 2nd generation devices has gained considerable popularity and helped to highlight important differences between devices. In a review article by White et al, entitled, ‘A critique of elective pediatric supraglottic airway devices’, a 1st generation device was described as a ‘simple airway tube’ and 2nd generation as a device that ‘incorporates specific design features to improve safety by protecting against regurgitation and aspiration.’

Of course, as mentioned in an earlier blog post on the classification of supraglottic airways, designation as a 2nd generation device does not in itself confirm superiority of performance, but the classification does provide useful information about basic product design characteristics, such as whether the device incorporates a mechanism for the management of regurgitant fluid. These are important considerations when deciding the most appropriate SAD to use in the pre-hospital setting.

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

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

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

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

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

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

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

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?