Is Penthrox a Wilderness Medicine Wonder-drug?

22 June 2023


Dr. Will Duffin – Joint Medical Director & GP

Will is a jobbing Devon based GP, educator and adventure addict. He has provided medical cover for dozens of very different expeditions and projects; including commercial high-altitude treks in The Himalayas and The Andes, a luxury Trans-Siberian private train, a reality TV show in the South Pacific and he has worked with UNICEF out in forgotten corners of Myanmar.

Managing the pain of acute trauma in wilderness settings has historically been a tricky area. Many expeditions don’t carry strong opioids due to difficulties with controlled drugs and border crossings. Very often the strongest analgesia available is co-codamol (30/500) and maybe some IV paracetamol. However, when you need something fast acting and powerful to reduce or immobilise a fracture and package a patient these options just won’t cut the mustard. 

Enter ‘the green whistle’: patient controlled analgesia in the form of the volatile anaesthetic methoxyflurane that is poured into a wick in the centre of the device and can be inhaled by the patient. The risk of off-gassing (and inadvertently anaesthetising the treating clinician!) is dealt with through an attached carbon filter. Even so, it must be used with caution in enclosed spaces and it’s for this reason it’s not yet approved for use in aircraft for fears of taking out the pilot. (Clearly, this would be a highly sub-optimal situation!) It’s not a controlled drug so you should have no difficult questions when it comes to those border crossings! 

→ Be sure to watch Dr Will Duffin, taking you through the benefits and usability of Penthrox…

Penthrox can give your patient 25-30 mins of continuous pain relief or up to 1 hour if used intermittently. I love the ‘dilutor hole’ which patients can put their finger over like a recorder to get an extra strong dose. Don’t forget to prompt the patient to breathe out through the mouthpiece where the activated charcoal in the device can catch excess vapour. 

Curiously, Penthrox has been used in Australia for about 30 years but was only approved for use in Europe in 2017 and has since exploded in popularity. It is currently available in over 40 countries (Ref 1)  It’s not currently used in the US due to fears of kidney injury, however it is in phase 3 trials and this may change in the next few years. In many UK Emergency departments Penthrox is now superseding tried and trusted nitrous oxide (gas and air). 

In many ways it’s ideal for wilderness settings. It’s light to carry and very easy to use. Once you’ve poured in the liquid and attached the carbon filter its ready to go. In major trauma you are likely to still need intravenous anaesthesia (if you have it) but at the very least it’s going to buy you time to make your initial assessment and management, including moving a casualty to safety or gaining 360 access. It’s so small and packable you could even carry it on your belt or in a pocket. 

The range of possible uses beyond just trauma are many. There’s a great case report of a patient undergoing Penthrox-assisted supra-pubic aspiration for urinary retention at altitude(Ref 2).  I’ve used it successfully to reduce an incarcerated inguinal hernia in a local villager on a remote island and was blown away by how effective it was.

But before you start dishing it out to everyone, be aware of its limitations. The manufacturers advise it should only be used in fully conscious patients with a pain score of 4/10 or higher. The main contraindication is ‘clinically significant renal impairment’ as there is a risk of AKI, but it should also be avoided in respiratory impairment, cardiovascular instability and ‘hepatic disorders’. 

If it’s something you’re thinking of adding to your med kit then be sure to do some up-skilling. The free online training at Penthrox University is a great start (Ref 3)

Disclaimer: This article is the author’s own unbiased opinion. There was no sponsorship or from the drug manufacturer. The device reviewed was purchased through the normal channels. 


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