Once Bitten, When to Fly?

It is very exciting to introduce Tim Wallace, flight nurse from the Top End, on a topic sorely neglected for a website coming from Australia – animals that can kill you. Actually, perhaps Tim can introduce Tim. 

“When I was a researcher working for a haematologist, I wanted to be a paramedic, but I ended up as a pedantic number chaser driving ventilators (ICU nurse). So I went to uni again so I could be a paramedic. Then I got this job and now I’m studying midwifery (I’ve been a uni student for 9 of the last 15 years). I came to Darwin then left after a couple of years and went rock climbing for a year with my now wifey. I thought the grass was greener down south. It wasn’t. I like Darwin. Finally, I think cats are the only malicious animal.

It’s 11 p.m. one night, in the middle of the wet season and a referral comes in for a suspected snake bite in Bulman. What? You don’t remember where Bulman is? Perhaps refresh your geography here.

Here’s the stuff you find out straight away:

  • A 34 year old male has been bitten by something on the foot.
  • He presented around 1 hour before the phone call with a story of walking along the road and stepping on a snake that then bit him. Bearing in mind that an Indigenous man from a very remote area like this is probably very familiar with the characteristics and behaviours of the local wildlife, this man says he didn’t see the snake, but felt it and has some marks on his left ankle that could be puncture marks.
  • He walked to the clinic (1km) and since then has had the leg immobilised and a pressure bandage applied.
  • His observations are unexciting and he is completely asymptomatic of any of the obvious signs (e.g. bleeding from cannula sites) or often subtle symptoms (e.g. abdominal pain) that might be associated with a snakebite.

So what do you make of a story like this? Well typically in a case like this a lot of emphasis is placed on the story as there are a lot of variables (and ambiguity) associated with confirming a snake bite and predicting the clinical course, including:

  • What first aid has actually happened? Was it immediate or delayed, effective or ineffective?
  • Timing: while a bite from a brown snake can be almost immediately obvious, death adder neurotoxicity may be delayed as long as 24hours.
  • Syndromes of envenomation have very poor specificity in general (see ‘syndromes of envenomation’ table/picture)
  • You often see dry bites where the snake digs in with the fangs but does not inject venom.
  • Then there are stick bites, such as: did not see snake, but felt something while walking in the bush at night.

Let’s Talk Logistics

Back to our patient – how will we get there?

Bulman is ~550km as the Kingair flies and is exceptionally isolated and now has no emergency medical services (as they are all tied up with this case). The strip is unlit and not suitable for night landings. While it is possible to get in using the helicopter, there is a large band of storms between us and Bulman that means a bumpy marathon of a flight in what one of my colleagues calls the ‘vomitron’, stopping for fuel via a detour to the north of Kakadu on the way there and back.

tindal radar copy

Yeah. It’s not going to be easy.


Are the Snakes Dangerous?

Well everything in Australia is designed to kill you and the Top End is the most Australian bit of Australia. We have some awesome elapids (hollow fixed venom injecting fanged snakes) up here and snakebite is an increasingly common emergency presentation (as you will see from our data). Australia sees ~3 fatal snakebites per year + occasional significant morbidity (e.g. mechanical ventilation, neurological sequelae at discharge).

This is the only one I have seen in the Top End in the 5 years I’ve been here.


Most of the mortality is associated with the brown snake family whose victims classically present with a story of early collapse and go on to develop VICC (venom induced consumptive coagulopathy) and occasionally signs and symptoms of neurotoxicity. In the Top End, in addition to the western brown, the other problematic species are the myotoxic king browns (mulga snake), neurotoxic death adders and less commonly the mighty taipan (VICC, neurotoxicity). Many of our retrieval registrars come from countries with boring fauna and this topic is very exciting for them.

syndroms of envenomation copy
Not very specific really. (This table is from the Isbister paper mentioned below.)
playing with snake copy
Fun fact: the bite reflex of some snakes can remain intact for over an hour after death. This is me playing with a dead brown snake brought in by CareFlight (with a patient) before I was familiar with the case reports of envenomation from dead snakes …

Having posed this scenario to a few of the retrieval consultants at CareFlight they all placed significant emphasis on how convincing the story was and all offered varying perspectives on the priority of retrieving this man. Remote clinics use the ‘CARPA Standard Treatment Manual’ protocols for managing emergency presentations, and CARPA is quite clear about snakebite:

CARPA snakebite copy

And we can’t assume the RAN was comfortable by herself with this guy in her clinic.

Bulmanclinic copy
It turns out that the capacity to deal with a sick person might be more limited than the hospital …

Despite the rigid proclamations of the CARPA manual, I reckon there are unanswered questions about when (and if) patients who are suspected to have been bitten by a snake should be retrieved. As I have alluded to, confirming a diagnosis over the phone is difficult and a lot hinges on how convincing the story is. With this in mind we decided to try and arm ourselves with some hard facts, undertaking an audit of our retrieval database to quantify the existing situation around suspected snakebite retrievals.

Lane dead snake copy
Maybe there’s another time to take the ex-snakes back to the city? (And the patients, of course.)


Let’s Talk Numbers

Interestingly, the numbers of retrievals have increased somewhat since the last published data:

– Currie (2004) – 8.6 year sample – 13.6 aeromedical retrievals per year

– Our audit – 3.8 year sample – 30.2 aeromedical retrievals per year

Why? We’re just not sure.

When it comes to confirmed envenomation we get to a very select group:

– 3.5% (4 of 115 patients) – we’ve used antivenom twice in this period

The comparison? Well previously published data for northern Australia has quoted 5-23%.

Why are those numbers for confirmed envenomation lower in our stats? We don’t quite know that either.

Then there’s the when – is there any particular time of day when the calls come in? Well ~65% of retrievals occur at night – see the slightly busy plot of night retrieval timings

day v night copy

Of course, the timing also has some implications for our pilots.


Flying High

In the Top End strips vary from well serviced, long, sealed, well lit and fenced in with GPS approaches (eg. Gove, Groote Eyeland) to poorly lit, narrow, occasionally dirt strips that are actually primarily the homes of kangaroos and buffalo and only occasionally used to land aircraft. The lights in many remote strips are solar, so they are great at 11pm but generally a lot less bright by 3am.

Crucially, many of these strips have no GPS approach. Where there is a GPS approach, the avionics aid the pilot in landing. Where there is no GPS approach, the pilots do a ‘visual circling approach’. What does that mean for safety? Well night flying is 3 times more dangerous than the equivalent aviation work  in daylight hours. A visual circling approach is 25 times (!) more dangerous than a GPS approach. 25 times. (As a sidenote, helicopter EMS operations are also more dangerous at night.)

Perhaps the best insight for the aviation lay-person is to watch this video of a visual night time landing filmed by one of my colleagues on an after hours retrieval.

How were you planning to get there again?

Back to the Bitten

Back to our dude in Bulman. The retrieval consultant, in consultation with the logistics coordinator and flight crew decided that the the face of apparent low risk to the patient and massive logistical difficulty in getting to Bulman and risk to the flight crew, it would be reasonable to delay the retrieval until daylight. He was retrieved in the morning to Royal Darwin Hospital where the path lab confirmed that there was no envenomation.

 The Big Questions

So we’re left with questions that really matter (like all the best bits of research). My questions for anyone who wants to chip in:

  • Based on the apparently low morbidity/mortality associated with snakebite and low incidence of envenomation in our data, can we justify the frequently high risk (night) flying associated with retrieving the group of patients without clear evidence of envenomation?
  • Would it be reasonable to delay retrieval of patients of ALL patients with no clinical evidence of envenomation until the morning?

Who is shooting for that runway at night? Who is already planning what they’ll have for breakfast first?

Well the good news is this is an ongoing project, so I’ll be updating when we have a bit more information.



This post arose from work presented at this year’s ASA conference. Here’s a bit more reading so you can go back to the sources.

Allen GE, Brown SGA, Buckley NA, et al. Clinical Effects and Antivenin Dosing in Brown Snake (Pseudonaja app.) Envenoming – Australian Snakebite Project (ASP-14). PLoS One. 2012;7:e53188. doi:10.1371/journal.pone.0053188. 

ATSB. 2012. Visual flight at night accidents: What you can’t see can still hurt you. 

Currie B. Snakebite in tropical Australia: a prospective study in the “Top End” of the Northern Territory. MJA. 2004;81: No. 11/12.

Currie B. Treatment of snakebite in Australia: the current evidence base and questions requiring collaborative multi centre prospective studies. Toxicon 2006;48:941-56.

Isbister G. Snake bite: a current approach to management. Australian Prescriber. 2008;29:5.

Sutherland SK. Deaths from snake bite in Australia, 1981-1991. Med J Aust. 1992;157:740-6.

And, if you’ve made it this far, remember you might like to follow the blog and you’ll get an e-mail with each post.




Getting Things Straight

Lots of beliefs are hard to shake. Andrew Weatherall covers one from the paediatric airway – the holy status of the straight blade.

As I’ve mentioned before, paediatric airway management is full of mythological beasts. Some of that is about anatomy stuff and the like. Some is about equipment. Plenty is about technique. Sometimes it’s about technique and equipment together. Bliss.

So this is where I wade into another topic in paeds airways:

Straight blades are overrated and you should throw them away.

Marc Zimmer Dog Unicorn Dog
It is a time for mythical beasts. Like the fabled unicorn dog but less cool.

Do we need big bins?

Well, actually no. Stop the indignant letter writing. When I say they’re overrated I don’t mean they have no value. They have a role like most items of equipment that are still in use after nearly 100 years probably still have a role.

What I do mean is that straight blades are treated with a reverence in paediatric airway management that is unwarranted, while curved blades like the Macintosh seem to be described as “bigger people’s airway devices”. Trainees could easily go through their whole training period thinking that you must always use straight blades for patients who understand what the hell Pokemon are all about.

That just isn’t true. People who swear by straight blades will point to the more anterior epiglottis and the angle of the cords to argue the case for their chosen device just as convincingly as those who like a curved blade point out that they get more working space in the mouth and a familiar blade and both will be sort of right.

It might be useful to dive into this a little more. So let’s work through a paper from 2014 that specifically looked at the straight vs curved blade question. Partly because it gives an appropriate ‘meh’ when trying to split the two options but also because it highlights how myths can dominate our perception of the original work.


Welcoming the Contenders

The paper here appeared in Pediatric Anesthesia in 2014 (I touched on this in the other post). The authors set out with a useful question: is there a difference between Miller and Macintosh blades when it comes to ease of obtaining a view and success of intubation in the 1-24 month age range?

They looked at well kids having elective surgery under anaesthesia where muscle relaxation was also used. They included 120 kids and each kid had laryngoscopy with one device then the other.

The results are a case of a big old shrug, which is sort of OK. Easy laryngoscopy was noted in pretty much the same percentages. First pass success pretty much the same. The rates of one being better for the view than the other were pretty much the same. When it was difficult with one view the rate of switching to the other and finding it was easier was about the same regardless of whether you had started with the Macintosh or Miller.

So the two blades that stepped into the ring step out with no knock out punch thrown. There are a number of other interesting points when you look in more detail though and a few comments I’d make in passing.

  1. The epiglottis isn’t the endpoint

I have this impression that trainees get really obsessed needing to pick up and control the epiglottis with a straight blade. In this paper the routine use of the straight blade was to place the tip in the vallecula. In only 2 of the 60 uses of the Miller blade did they pick up the epiglottis.

Why do people get so antsy about picking up the epiglottis? It was only ever described as one of the options to obtain the view, not the only option. Those early designers never forgot the aim: to obtain a view to let you instrument the trachea.

Here’s Miller from the paper where he described his blade:

“The epiglottis is visualized and raised slightly to exposure the cords or, if the operator desires, the tip of the blade maybe placed in front of the epiglottis and raised sufficiently to visualize the cords after the method of Macintosh.”

In fact Macintosh described the straight blade being used in this manner when he reported on his own design, singling out Dr Margaret Hawksley as an exponent of this technique. The authors of this recent paper further point out that it’s a lot more stimulating to pick up the epiglottis. That’s worth at least a thought.

Miller wasn’t precious about how you get the view. The idea that picking up the epiglottis is the only technique just got repeated enough that no one remembers to question it. The epiglottis isn’t the main game. The view is the thing.

  1. Make sure of your basic technique

One of the other interesting features here is that there are some elements of the intubation technique that seem like they could do with a review. An example: the Miller blade was advanced centrally along the tongue. This is a technique taught by heaps of people and I think Miller probably would have strong feelings about that. Again let’s go back to the paper:

“The blade is inserted in the right side of the mouth, pushing the tongue to the left.”

One of the bigger challenges in getting a view in paediatric patients is getting the tongue out of the way. This is particularly for straight blades which tend to have less of a flange to do some of the work for you. I’m not the only one who thinks so, either:

“On passing the instrument into the mouth the tongue should be manipulated to the left side, away from the slot; otherwise the organ may roll into the barrel and completely obstruct the view.”

That was Magill. In 1930. Now Magill might have been describing the use of a speculum but the principle is the same. The tongue is only likely to make your view worse (and given that straight blades pose an additional challenge in having not as much space proximally to work in, that really matters).

Magill went on to point out that if you struggled at all you could move the proximal end of our instrument further to the right corner of the mouth – that’s also known as the paraglossal view and turns out to be pretty much the best way to go.

In other basic technique points the authors of this recent paper mention that laryngoscopy was done with the head in a neutral position. This doesn’t seem like optimal head positioning for use of either blade, and that’s another point worth keeping in mind.

  1. It’s useful to know what the intended use was with your instrument of choice

In this paper and in the comparison with the Cardiff blade they refer to as an example of other “blade vs blade” papers, a comment is made that when you introduce an endotracheal tube centrally you can compromise the view and that it’s not great for introducing your tube via any central channel.

Miller, again:

“The scope is used for visualizing the cords only. One should work outside the blade to insert the tube. The only criticism of the instrument has been that it is too small through which to work. It was not designed to be used as a guide for the catheter.” (That’s the author’s work with the italics, not an edit from me.)

In fact Miller searched for a new design because he felt small laryngoscope blades on the market were too big. It’s designed to be small.

So yes, you need to use a technique where you bring the tube in from the side. That was always the point.

  1. Should we stop talking about external laryngeal manipulation like it’s an extra?

This is really a bit of open musing on my part. This was done in over 50% of the patients in both groups and generally helped when it was used. I can see how the precision of description goes up when we include these details but it strikes me as so much a part of every intubation (as this external pressure means less work for the laryngoscope itself) that I wonder how much it adds to our appreciation of clinical use. That’s one for the comments section I guess.

Messages for the Prehospital or Retrieval Type

After sifting though all of that, what are the take home messages? Well, here are some from me that might need additions from others:

  1. Know what you do and why you do it

Those picking up a laryngoscope for the little people need to have thought through what they will use and why. If I’m offered a personal preference it is to use a curved blade for everyone. Even as a paeds anaesthetist I’ve just used a curved blade more. It’s better designed to control that pesky tongue. You get a huge working space within the mouth and with external laryngeal manipulation (which I’d call standard) you can pretty much always bring the airway into view, even in the slightly anterior larynx.

I haven’t seen a study that would confirm this hunch, but I wonder if one of the problems some prehospital clinicians have with paeds intubation is they pick up a laryngoscope they didn’t really learn, very rarely use or rehearse with and don’t really understand. You need to focus your technique slightly differently with a straight blade. Add the stress of the situation and is it any wonder the job becomes harder?

I’d back the occasional proceduralist as more likely to intuitively understand the anatomy using the same sort of blade they always use. I doubt it’s a study that would be easy to set up in anything but mannequins though.

  1. Know the different options

That preference for people using what they know doesn’t mean you shouldn’t learn both. This study did highlight that some kids just have a better view with a particular blade. You can’t quite get as good a view with one option, switch to the next and all of a sudden it’s easier. Again though if you’re reaching for that other option use it right.

  1. Make your technique appropriate for the 1% and the 99% will be fine

This is more of a general point. Laryngoscopy in infants is easy the vast majority of the time. So if you don’t bother controlling the tongue you’ll probably get by most times. It’s the 1% where your routine practice of not getting the tongue out of your view, or being able to aim for either the vallecula or epiglottis, or positioning the head right will start to bite.

If you always do everything to maximise your view, you’ve already got a good technique for the 1%. It’s best not to need to review your technique once the blade is in and you’ve figured out this is the tough one you’ve been dreading.

So after all that, maybe paediatric airway instrumentation comes down to a really simple refrain: the tool in the hand matters less than the tool holding it.



That image comes from Marc Zimmer on flickr under Creative Commons and is unaltered.

Here’s the paper mentioned again:

Varghese E, Kundu R. Does the Miller blade truly provide a better laryngoscopic view and intubating conditions than the Macintosh blade in small children? Pediatric Anesthesia 2014;24:825-9. 

And the others …

A review on the popularity of the Macintosh blade:

Scott J, Baker PA. How did the Macintosh laryngoscope become so popular? Pediatric Anesthesia 2009; 19 (Suppl 1):24-9. 

Miller RA. A new laryngoscope for intubation of infants. Anaesthesiology 1946;7:205-6.

Macintosh RR. A new laryngoscope. Lancet 1943;1:205.

Magill IW. Technique in endotracheal anaesthesia. British Medical Journal 1930;2:817-20.

and the Cardiff paper:

Jones RM, Jones PL, Gildersleve CD, et al. The Cardiff paediatric laryngoscope blade: a comparison with the Miller size 1 and Macintosh size 2 laryngoscope blades. Anaesthesia, 2004;59:1016-9.