Snakebite

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‘Ready?’. ‘Yeah I’m ready, lets start’. We turn on the IV drip and  watch the pale yellow antivenom start to trickle in. I keep an eye on the monitor. Oxygen saturations and pulse are stable. We are surrounded by all of the gear needed for intubation, including anaesthetic drugs, and I have drawn up several doses of the drugs needed to treat anaphylaxis. We gave the boy a shot of IM adrenaline before we started. I am with one of my colleagues, on high care at the end of our night shift. I’d just settled down to try and catch a few hours sleep when I had a call at 5am to tell me that the blood tests were back for an 8 year old boy who had been bitten by a snake at midnight. There was an abnormality with his blood clotting. I reviewed him and the swelling from the site of the bite on his foot was also spreading up his leg quite quickly, so antivenom was required.

The trouble with antivenom is that it is dirty stuff. During my Diploma in Tropical Medicine in Liverpool we were treated to seeing a clinical specialist and a herpetologist envenomate some snakes by getting them to bite down on an empty glass container and then milking their glands. They freeze dry this venom, mix it up with the venom from other snakes from the same geographical region and they inject it into horses. The horse makes antibodies to the venom which are present in the blood. Horse blood is drawn and spun down so you are left with the antibody-containing serum which is essentially what antivenom is (once it has been purified a bit). The trouble is this also contains a whole host of horse proteins which human blood doesn’t like – so the risk of having an allergic reaction or even anaphylaxis is high. Reaction rates for South African antivenom are quoted as 50%, but anecdotally it is even higher.

As the infusion ran, an urticarial rash developed on the boys face. We gave steroids and antihistamine and a further dose of adrenaline. His breathing remained ok and he maintained his heart rate and oxygenation. Lip swelling developed and he needed yet more adrenaline and some fluids, but as the infusion finished, it all started to settle down. It was a scary experience giving such a dangerous treatment to a child and one you wouldn’t do lightly.

Snake bites tend to cause one of three main problems: cytotoxicity (cell or tissue damage), neurotoxocity (nerve damage or paralysis) and haemotoxicity (problems with the blood and blood clotting disorders). Neurotoxic are the most scary I think as people can stop breathing as their respiratory muscles become paralysed. Fortunately for us, most of our snakes are cytotoxic and usually just cause a bit of pain and swelling, but the consequences can still be severe. I had to transfer one lady out as the severe pain, swelling and tissue damage was spreading up her arm. Another patient this week had a necrotic wound at the site of the snake bite. We have had some frightening cases in the hospital recently. One apparently minor snake bite patient suffered a sudden death on the ward. Another child was bitten on the face. As the swelling spread his airway was at risk so he had to be intubated and helicopter transferred out. So when I was faced with a patient in clinic this morning with a snakebite to the ankle and a frustrated nurse telling me that there were no ambulances I stood my ground. Yes he did need to go to hospital for blood tests and no he couldn’t travel in the minibus (immobilisation and elevation of the limb are important parts of management.  Tourniquets  are out!).

Why do people get bitten? Most of our patients live in close contact with nature. Off the mainroads, tracks are mud or dirt and they don’t have concrete driveways of electric streetlamps. When we are on call, we have to walk a sandy path under the mango trees up to hospital and I always take a head torch – once I saw a green snake whizz out in front of me (I’m  still not sure if it was a green mamba or natal green snake). So whilst most snakes are not predatory, it isn’t too hard to disturb them. We have a snake-obsessed doctor in the hospital so whenever anyone arrives with a dead snake in a bag to OPD, he will pop up and have a look to see if he can identify it. If anyone finds a live snake in the grounds, then he will gladly volunteer with his snake hook and take it home in a ventilated snake box to await it’s release!

Some of the Liverpool team were working hard on a project using camels instead of horses to create an anti-venom that is less allergenic, and they were aiming for a pan-african recipe to cover all the relevant snake species. Unfortunately some ruthless pharmaceutical types but a block on the development but I hope they can get the work off the ground again to create a treatment that is much safer for our patients. Until then, watch out in the long grass…

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