Tuesday, May 7, 2013

Three things I learned: snake envenomation in dogs and cats

This little snake doesn't intend any harm - and many don't, but snake envenomation
 is common in Australian dogs and cats.

The ASAVA hosted a webinar on snake bite envenomation, fortunately a condition very rarely seen in inner-Sydney. Dr Peter Best, a specialist based at South Tamworth Animal Hospital, clearly knows everything there is to know about snake bite envenomation right down to the molecular level.

Every year there are an estimated 6,000 snake bite envenomations of dogs and cats in Australia, with jack Russell terriers and Siamese cats overrepresented. (Am I alone in being surprised about Siamese cats?) – although Dr Best did point out that survival rates in cats were likely higher because cats are more agile and therefore may not get the full dose of venom. Of the humans affected, herpetologists and young, inebriated blokes are overrepresented (still more surprised about the Siamese cats).

More good news is that up to 50 per cent of bites did not result in envenomation – either because no venom was delivered or it didn’t penetrate skin.  But it’s impossible to be sure – even if you run diagnostics.

I could easily list 30 things I learned in this presentation, but the three main points I learned were:
a)      Onset of signs can range from minutes to 25 hours. That means that animals with suspected envenomation should be admitted for observation for 25 hours – and if they do deteriorate they can deteriorate rapidly.

b)      Dogs with pre-paralytic signs (i.e. vomiting, salivation, mydriasis and transient collapse) can recover – but the fact that they exhibit these signs mean they have had a potentially lethal dose. They need to be treated with anti-venom immediately. As with all things cats are a bit less obvious, being a bit weak and wobbly

c)       In human medicine the current trend is to give a fixed amount of anti-venom, but according to Best and his team this strategy does not work in dogs and cats. He recommends providing intermittent, positive pressure ventilation (IPPV) and administering anti-venom vials repeatedly (at intervals of around 10-30 minutes) until spontaneous ventilation occurs. (He pre-meds his patients with an IV antihistamine and a SQ dose of adrenalin).  One dog his team treated for brown snake envenomation required a staggering 13 vials of anti-venom (oh, and also two packs of whole blood, one of fresh frozen plasma and artificial ventilation for 36 hours). He survived.
It was an inspiring presentation,  based on a huge amount of clinical experience integrated with solid theory.