Snake bite

Snake bite

Current treatments for Australian venomous snake bites, including sea snake bites

Pressure-immobilisation is recommended for all Australian venomous snake bites, including sea snakes. This technique was developed in the 1970's by Professor Struan Sutherland. Its purpose is to retard the movement of venom from the bite site into the circulation, thus "buying time" for the patient to reach medical care. Research with snake venom has shown that very little venom reaches the blood stream if firm pressure is applied over the bitten area and the limb is immobilised. Pressure-immobilisation was initially developed to treat snakebite, but it is also applicable to bites and stings by some other venomous creatures.

First Aid In the most recent published survey of deaths from snakebite in Australia (Sutherland and Leonard 1995), twelve deaths were reported over the three year period (1992-94); in none of these cases was effective first aid employed. The pressure-immobilisation method of first aid has been well described and its efficacy in elapid envenomation has been shown both clinically and in the laboratory. It is recommended for use in bites by all Australian venomous snakes. Pressure bandages may be cut away from the bite site to allow swabs to be taken for venom detection and new bandages quickly applied over the site. Once the patient has reached hospital and the appropriate antivenom and other drugs have been assembled, first aid measures may be removed. Bandages and splints should not be left in place for prolonged periods once the patient has reached adequate medical facilities. If on removal of first aid measures, the patient’s condition deteriorates, the bandages can be re-applied while antivenom is administered. It is preferable that such treatment takes place within a critical care area of the hospital, such as intensive care or the emergency department, where complications arising from envenomation or reactions to antivenom can best be managed.

Initial Hospital Management of Snakebite Once the patient reaches hospital, initial management consists of obtaining intravenous access and resuscitation if required. If possible, a careful history and examination should be undertaken with reference to the features described above, as well as previous envenomations and allergies to antivenom or to horse serum. This will assist in diagnosis and aid decision-making with respect to definitive treatment. Samples for venom detection and for pathology should be obtained, and an attempt made to identify the genus of snake if possible (see below). When an intravenous line is in situ and antivenom and resuscitation facilities, including adrenaline, are assembled, then first aid measures may be removed. Bandages and splints should not be left in place for prolonged periods once the patient has reached adequate medical facilities. If on removal of first aid measures, the patient’s condition deteriorates, the bandages can be re-applied while antivenom is administered. It is preferable that such treatment takes place within a critical care area of the hospital, such as intensive care or the emergency department, where complications arising from envenomation or reactions to antivenom can best be managed. If the patient has not developed any symptoms or signs of envenomation, nor any indication of coagulopathy or myolysis on blood taken 4 hours after the removal of first aid (or after the bite if no first aid was used) then the patient has probably not sustained a significant envenomation, although delayed onset of symptoms up to 24 hours have been described.

Choice of Antivenom Identification of the offending snake will aid in the choice of the appropriate antivenom and alert clinicians to particular features characteristic of envenomation by that type of snake. In cases of snakebite involving zoo staff, herpetologists or other experienced snake handlers, the snake’s identity may be known (although this cannot always be relied upon, particularly in the case of enthusiastic amateurs). Identification of snakes by the general public or by hospital staff is frequently unreliable. Sometimes, the snake is not seen, or is only glimpsed in retreat.

Indications for Antivenom Many cases of snakebite do not need antivenom because often the snake injects very little venom. Fang marks alone are not an indication for antivenom. Antivenoms should not be used unless there is evidence of systemic envenomation.

Presentation of envenomation may include:

headache, nausea, vomitingAbdominal paincollapse, unconsciousness (may be transient), comapainful, tender muscles (myolysis)blurred visionirritability, confusiondark urine (myoglobinuria, haematuria)ptosis, dysarthria, weakness/paralysis, dyspnoearespiratory failure (neurotoxicity)hypotensioncardiorespiratory arrest When envenomation is not indicated, presentation of a snake bite may include: Puncture marks (usually on limbs). These may be difficult to see, and may consist of a single or double puncture or scratch marks or multiple punctures. They may be bleeding or oozing.(NB care should be taken with puncture of arterial or central venous sites in the presence of potential coagulopathy) Regional tender lymphadenopathy (NB this may also be present after bites from non-venomous snakes, and is not by itself an indication for antivenom)Methods for investigating envenomation include: Venom Detection Kit (bite site, urine or blood) Clotting studies INR/PT, APTT, ACT, D-dimer, X-FDP, fibrinogen. In remote areas where sophisticated clotting tests are unavailable, a sample of the patient’s blood in a plain tube should clot within a few minutes in the absence of coagulopathy Creatine kinase for myolysis Urinalysis for haemoglobin, myoglobin Renal function may be impaired secondary to myoglobinuria or other mechanisms WCC is usually only mildly elevated. A significantly raised WCC may indicate other pathology. Differential diagnosis of venomous snakebite non-venomous snakebite bite or sting by other venomous creature (arthropod (including spider), octopus, jellyfish) CVA ascending neuropathy e.g. Guillain-Barre Syndrome AMI allergic reaction hypoglycaemia/hyperglycaemia drug overdose closed head injury Snake venom is a complex mixture of toxic and non-toxic substances, mostly proteins. Australian snake venoms display neurotoxic, haemolytic, pro-coagulant and usually weak cytotoxic properties. Some also contain potent myotoxic activity. The composition of particular venoms influences the clinical presentation of particular snakebites. The symptoms and signs of envenomation, and the time course they follow, vary enormously between individual patients, being influenced by such factors as body weight, amount of venom injected, age and state of health of the patient time elapsed since the bite and site of the bite. Variation between snakes is also important. The size and maturity of the snake and the time since it last injected venom will influence the severity of the envenomation. Some features of envenomation are more prominent in bites from certain species of snakes. Myolysis, for example, is particularly prominent in sea snake and tiger snake envenomations, while death adder venom is predominantly neurotoxic in action. Myolysis may lead to renal failure, which probably accounted for the delayed deaths at 2-7 days described in the past. Several Australian snake venoms, including tiger snake and taipan venoms, contain post-synaptic as well as pre-synaptic neurotoxins, the latter being difficult to reverse if the patient is not treated promptly. Coagulation disturbance, usually related to secondary afibrinogenaemia, is common after bites from most Australian venomous snakes, although severe haemorrhage is rarely seen. There have been 7 published fatal cases of intracerebral haemorrhage related to snakebite in Australia.

Snake bite

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