Snakebites medical therapy
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Medical Therapy
Medical Management of Snake Bites
- Only 1 in 20 snake bites require active emergency treatment or the administration of antivenom. Medical management depends on the degree of systemic envenomation and the type of venom.
Critically Ill Patients
- Maintain immobilization, splint and bandage until the situation is under control.
- Support airway, breathing and circulation.
- Intubate and ventilate with 100% Oxygen if airway or respiration fail.
- Obtain toxicology consultation
- Give antivenom immediately. Intravenous epinephrine should be given only for life-threatening hypotension or anaphylaxis - its use has been associated with cerebral hemorrhage.
- Volume expansion may be necessary.
- Severe coagulation disturbances, electrolyte abnormalities, and muscle damage leading to acute renal failure are likely.
- Repeat antivenom as clinically indicated.
- General management as for less seriously ill patients as well (see below).
Less Seriously Ill Patients
- No signs of systemic spread
- Admit to ICU for non-invasive monitoring, strict bedrest and full head injury observations (wake hourly).
- Leave bandages in place.
- Obtain toxicology consultation
- Obtain appropriate antivenoms and venom detection kit.
- Obtain intravenous access.
- Take blood for group and X-match, coagulation screen (including fibrinogen levels, and tests for DIC), full blood count, electrolytes and calcium, creatinine kinase and arterial blood gases. Perform ECG. Repeat at appropriate intervals.
- Collect urine for microscopy to detect hematuria and for free protein, hemoglobin and myoglobin measurement. Record urine output. Freeze the first sample for venom detection.
- Draw up drugs in case of anaphylaxis to antivenom.
- When ready, cut a hole over the wound site, inspect and take swabs for use with the venom detection kit.
- Once the results of the venom detection kit are known, slowly and progressively remove the bandages.
- If systemic symptoms ensue:
- Re-apply bandages and give antivenom as clinically indicated.
- Ensure the patient is well hydrated (to reduce the risk of acute renal failure due to rhabdomyolysis).
- Repeat blood tests, ECG, etc at clinically relevant intervals.
- Correct abnormal coagulation; look out for disseminated intravascular coagulation (heparin probably contra-indicated in DIC from snake bite).
- Analgesia and sedation - be cautious.
- Correct hypotension, if present, with volume expansion and vasopressors (exclude occult bleeding).
- Watch for development of renal failure - monitor urine output and composition.
- Tetanus prohylaxis is recommended.
- Usually, if there are no signs of envenomation four hours after removal of the bandages, and if repeat blood tests taken at that time are normal, then it is probable that significant envenomation has not occurred. If laboratory tests are not available, 12 to 24 hours is a reasonable period of observation.
First Aid For Snake Bites- What NOT To Do
Though U.S. medical professionals may not agree on every aspect of what to do for snakebite first aid, they are nearly unanimous in their views of what not to do. Among their recommendations:
- No ice or any other type of cooling on the bite. Research has shown this to be potentially harmful.
- No tourniquets. This cuts blood flow completely and may result in loss of the affected limb.
- No electric shock. This method is under study and has yet to be proven effective. It could harm the victim.
- No incisions in the wound. Such measures have not been proven useful and may cause further injury.
- Do NOT wash the area of the bite. It is extremely important to retain traces of venom for use with venom identification kits!
- Stop lymphatic spread - bandage firmly, splint and immobilize. The lymphatic system is responsible for systemic spread of most venoms. Significant lymphatic spread of the venom can be arrested by complete immobility of the affected part and the application of a firm bandage (as firm as you would put on a sprained ankle) over a folded pad placed over the bitten area. The bandage should be applied immediately, starting at the bitten area and then extending from the periphery towards more central parts of the body. Bites to the head, neck, and back are a special problem - firm pressure should be applied locally if possible.
- Immobility is best attained by application of a splint, reassurance and immobilization (eg, putting the patient on a stretcher).
- Removal of the bandage will be associated with rapid systemic spread. Hence ALWAYS wait until the patient is in a fully-equipped medical treatment area before bandage removal is attempted.
Pharmacotherapy
Acute Pharmacotherapies
- Antivenoms
- Antivenom should be given to all patients who exhibit signs of systemic spread. One ampule (50ml of 17% protein) should neutralize the average venom yield from milking a snake of that species, and is usually enough for all but the most severe envenomations. Severe bites may require much more (up to 20 times the recommended dose!). If the situation allows, antivenoms should be given slowly (over half an hour, diluted in an IV fluid). A test dose may be advisable, particularly following prior exposure to equine protein.
- Antivenoms are prepared from horse serum. The risk of anaphylaxis is very low (less than 1% even for polyvalent antivenoms), but is increased in people who have had prior exposure to horses, equine tetanus vaccines, and a general allergic history. This increased risk is much more common in people aged 50 years or more. About 4% of all administrations are associated with minor reactions.
- Pre-treatment with a non-sedating anti-histamine (ie, promethazine 0.25 mg/kg), subcutaneous adrenaline (0.25mg for adults, 0.01mg/kg for children), and IV steroids (hydrocortisone 2mg/kg) is still recommended, although severe reactions are rare. In general the risk from the snake toxins is much greater than the risk of administering the antivenom.
- If an antivenom is administered, ALWAYS advise the patient of the possibility of delayed serum sickness (up to 14 days later). This is characterized by fever, rash, generalized lymphadenopathy, aching joints and renal impairment. The likelihood of developing this depends on the volume of antivenom required. It occurs in about 10% of patients who are given polyvalent antivenoms. Treatment with steroids is usually all that is needed. Shelf life is 3 years when stored in a refrigerator. Antivenoms should not be frozen.