Category Archives: Procedures

Delayed sequence intubation, apnoeic ventilation, and preventing desaturation (plus podcast)

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‘Delayed sequence intubation’ and ‘apnoeic ventilation’ are two of the hottest topics in ED airway management at the moment. Details and discussion of these topics are all over the internet currently (multiple links coming below!) so what I will provide now are BRIEF summaries of the concepts.

The relevance to our HEMS is that both of these techniques for delaying the time to desaturation during intubation should (in theory!) translate well to the prehospital environment, and provide additional weapons in the prehospital airway management arsenal.

Traditional Rapid Sequence Intubation involves:

1) a period of pre-oxygenation

2) simultaneous administration of an anaesthetic induction agent and a paralytic

3) intubation once sedation and paralysis is adequate

The problem with rapid sequence induction in the ED setting is that the sicker the patient is, the quicker they will desaturate once they are paralysed, and the less time the intubating clinician has to pass an ETT. This is the case particularly in patients with severe lung disease.

So how can we give ourselves longer to pass the ETT before the patient desaturates?

Apnoeic ventilation, the evidence behind it, and other significant considerations in intubation are described in this landmark paper by Scott Weingart (emcrit.org) and Richard Levitan (airway guru). They make the following points:

1) pre-oxygenation using non-invasive ventilation will recruit collapsed alveoli and provide more of a reservoir of oxygen in the lungs – especially useful in high risk patients, or those who are hypoxic to start with

2) prexoygenation provides a longer time to desaturation when the patient is sitting up

3) during the apnoeic period (after the administration of a paralytic) doing a jaw thrust will maintain a patent connection between the mouth and the glottis, and the patient will continue to oxygenate (although CO2 will rise)

4) having a nasal cannulae running at 15L/min during the apnoeic period (after a paralytic has been administered) will provide near 100% oxygen to the pharynx

(Items 3 and 4 above comprise APNOEIC VENTILATION)

4) during the apnoeic period, having the patient positioned with their ear at the same level as their sternum will provide the best view for laryngoscopy

DELAYED SEQUENCE INTUBATION is described in this paper by Scott Weingart. It is an unfortunate fact that many of the patients who most desperately need effective preoxygenation (hypoxic, hypercarbic) are unable to receive it because they are too agitated and combative.

One of the models Dr Weingart uses to describe DSI is “a procedural sedation, the procedure in this case being effective preoxygenation”.

The DSI procedure involves administering ketamine (chosen for its safety profile and preservation of airway reflexes and spontaneous respiratory effort) at a dose of 1-1.5kg, followed by pre oxygenation (with consideration of NIV pre oxygenation), followed by administration of a paralytic and intubation.

This podcast from prehospitalmed.com is a great interview of Scott Weingart by Minh Le Cong, discussing DSI in detail.

Minh Le Cong has also collated some resources regarding DSI here, including a formal protocol incorporating DSI and apnoeic ventilation and a detailed slide set from Dr Rob Bryant, Emergency Physician in Salt Lake City, Utah (note – decision-making regarding suitability for intubation/ICU admission is clearly different in the northern hemisphere!)

Aided greatly by the internet, these techniques have “gone viral” amongst emergency physicians and are being used with success in the ED setting. They are also making their way into the prehospital world.

With regards to the Auckland HEMS, the following considerations may be relevant:

1) For patients with lung disease, fitting a PEEP valve will allow delivery of CPAP pre oxygenation. In the setting of trauma and potential pneumothorax however, there may be significant risks

2) A jaw thrust during the apnoeic period and adminstering O2 at 15L/min via nasal cannulae are easy interventions prehospital. Given that all our prehospital RSIs to date have occurred at scenes with St John’s ambulance already in attendance, we are highly likely to have additional oxygen sources available for apnoeic ventilation beyond what we carry in the helicopter

3) While delayed sequence intubation has been described for patients with agitation due to hypoxia, there is no reason we can’t use it for patients with agitation due to other causes, for example the intoxicated patient with a moderate TBI. Even in the ED setting these patients are difficult to intubate, with a traditional RSI typically requiring multiple security guards/orderlies, and a rather desperate ‘quick and dirty’ one!  The particular relevance to HEMS is that the DSI procedure is targeted at the patient group (agitated, combative)  who are probably the WORST group to transport in a helicopter without intubating them (cramped environment, difficult ergonomics for restraint/sedation, more difficult monitoring, lots of equipment/emergency exists in close proximity…)

There are some caveats to us adopting these techniques however, especially DSI. The prehospital evidence base currently is (probably!) nil. In the podcast above, pod Scott Weingart describes his concern that someone will modify the DSI procedure (either via drugs or technique), cause a catastrophe, and ruin DSI’s reputation forever. Certainly there is significant concern from some anaesthetists who feel that the concept is “crazy”.

Prehospital RSI remains a controversial topic, mainly because the evidence base that it is beneficial is small compared to the evidence base that done badly it worsens outcomes (great summary of these issues in a slide set here by Tony Smith, one of our HEMS doctors who is both an intensivist and the medical advisor to St Johns ambulance).

Auckland HEMS trains extensively in RSI to ensure that it is safe and effective. St John’s Ambulance also have a good understanding of the procedure, with the result being that they can be valuable assistants when we perform an RSI. They also share with us the ‘mental model’ of what we are doing and why we are doing it. If we attend a scene, attempt the novel and relatively unproven DSI procedure based on good sense but little evidence, and have a poor outcome, we would probably be judged fairly harshly.

St John Ambulance Clinical Practice Guidelines 2011-2013

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With current dispatching protocols, most of the primary HEMS scenes we attend already have St John’s Ambulance present managing the patient. With this in mind, it is important for us to be aware of the treatment protocols they may have used on the patient.

The most current version of the St John Clinical Practice Guidelines is here:

Clinical Practice Guidelines

Pre-hospital thoracotomy

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One of the potentially life-saving interventions that a HEMS service can offer is pre-hospital thoracotomy in the setting of penetrating chest trauma and cardiac arrest at the scene.

Pre-hospital thoracotomy is well described in the literature, with good outcomes reported. The London HEMS group recently published a case series of 71 patients who underwent pre-hospital thoracotomy following stab wounds to the chest with cardiac arrest at the scene. Of these patients, 13 survived, and 11 had a good neurologic outcome.

The main issue with pre-hospital thoracotomy for the Auckland HEMS service is that while this intervention may be lifesaving, the frequency with which we would expect to have to perform it is extremely low, and therefore training and skills maintenance are extremely difficult. (Having said this, one of the Auckland HEMS doctors encountered a patient with penetrating chest trauma on his first ever (!) HEMS job, and was at most several minutes away from dealing with his patient arresting and the indication for prehospital thoracotomy being present. This patient was moribund on arrival to hospital, and underwent an ED thoracotomy prior to transfer to OR. The outcome in this case was excellent.)

The vast majority of significant trauma that occurs in the New Zealand region occurs via a blunt mechanism. The Auckland Hospital Trauma Service, who maintain an extensive database of trauma cases presenting to Auckland Hospital, published a review in 2011 of penetrating thoraco-abdominal trauma, which revealed that between 2003 and 2008 there were only 42 cases.

As a result of this, thoracotomy in ED in Auckland is an extremely rare event – probably about one per year, and these are usually performed by the surgical service rather than an ED physician. Such low frequency means that there is not really a measurable standard of care amongst ED physicians for ED thoracotomy, let alone pre-hospital thoracotomy. Mr Ian Civil, the director of the Auckland Trauma service, argued in a 2010 editorial in Emergency Medicine Australasia that the availability of surgical services in larger hospitals means that it does not make sense to train ED physicians in thoracotomy.

Considering prehospital thoracotomy in the context of the Auckland HEMS service, the situation is completely different. To load a patient at the scene, make even a short flight, and deliver the patient to a resuscitation area with a waiting trauma team, at least 15 minutes is required. If the patient has ANY signs of life at the scene, I suspect most of us would opt for immediate transport, but if the patient arrests at the scene, without a thoracotomy they have no chance of survival given the transport time to ED.

With this in mind, the Auckland HEMS service needs to consider how we would train for this eventuality and how the procedure would be performed in practice. Although several members of our team have prior experience in prehospital thoracotomy (one worked in prehospital care in Glasgow!), most have very little experience aside from very occasionally assisting the surgical service in the resuscitation area.

Rather than reinventing the wheel, we could start by using resources that have been created by services far more experienced in this than us.

The London HEMS service has posted their thoracotomy S.O.P. on their website. It is the best summary of the procedure I have encountered that reflects the sort of equipment we carry (not a rib spreader to be seen). An open access pdf from EMJ by some of the same authors is here, and contains additional commentary and photos.

London HEMS training for thoracotomy includes one-on-one training on techniques for opening the chest and internal cardiac massage, including use of video footage and a dedicated thoracotomy mannequin. While it would be difficult to justify obtaining a dedicated thoracotomy mannequin currently (our general purpose low fidelity mannequin is in dire need of replacement first!), between the HEMS group and the Auckland Surgical Services we have individuals with the necessary experience to provide tuition to the rest of us.

In the meantime, video resources are available here:

Standard L side thoracotomy, showing opening of the intercostal muscles with scissors, and vertical incision of the pericardium between two sets of forceps

Standard L side thoracotomy with audio explanation on a cadaver

Video demonstrating clamshell incision, cutting across sternum, and opening chest. Note the London HEMS S.O.P. includes the thoracotomy incisions being extended to the posterior axillary line bilaterally in order to provide good exposure without the need for rib retractors

Second half of this clip shows part of the London HEMS training in prehospital thoracotomy

Here is a great post by David Menzies from emergencymedicineireland.com, about the learning points from his first (and only) thoracotomy

Full text pdfs for this post are available here (secure area limited to ADHB staff only – ADHB has subscription access for staff to these journals through the Philson Library at the University of Auckland School Of Medicine)