Management

Any history suggestive of snakebite should prompt the initiation of first aid, investigation, and observation, as detailed below. The pressure bandage should remain in place until the patient can receive antivenom. Once in a suitable facility, bandages and splints should not be left on for prolonged periods, as venom is then not available for interaction with circulating antivenom. In addition, there is no evidence that venom is inactivated by being trapped at the bite site. 8 If the patient's condition deteriorates immediately after bandage removal, the bandages may be reapplied while antivenom is given. Snakebite cases often present a number of complex clinical problems; therefore early consultation with an expert is recommended.

The Commonwealth Serum Laboratory (CSL) Snake Venom Detection Kit (SVDK) detects snake venom in the urine or at the bite site, identifies the type of snake involved, and provides guidance in antivenom selection if antivenom is needed. Positive SVDK identification of venom at the bite site or in the urine is not an indication for antivenom therapy without other evidence of systemic venom effect. False-positive and false-negative results have been described for blood testing by the SDVK and so should not be used.8

Antivenom should be given only in cases when there is clear clinical or laboratory evidence of systemic venom effect. Clinical indications for immediate antivenom therapy include vomiting and severe headache; neurotoxic effects such as ptosis, cranial nerve involvement, progressive muscle weakness, or diaphragmatic involvement; or evidence of coagulopathy. Pertinent investigations include full blood count, serum electrolytes, renal function, creatine kinase levels, and urine testing for hematuria or myoglobinuria.9 Abnormal renal or coagulation studies may provide laboratory evidence of systemic venom effect before neurotoxic effects are apparent. If prothrombin time or activated partial thromboplastin time are prolonged, then levels of fibrinogen and fibrin degradation products should be obtained.

In the absence of clinical or laboratory evidence of venom effect, the elastic bandage should be removed and the patient observed for 12 h. Delayed envenomation after benign presentation has been documented. If significant envenomation has occurred, most patients will develop clinical or laboratory evidence of envenomation within 2 h of removing a bandage.8 Therefore, coagulation studies should be repeated 2 h after bandage removal and at intervals thereafter, depending on the patient's condition.

Five antivenom products, derived from equine IgG, are produced by the CSL to treat envenomation by certain groups of Australian snakes. These are termed monovalent antivenoms. A polyvalent antivenom, also equine IgG, neutralizes the venom of all five major groups of dangerous Australian snakes. The reader is directed to more detailed sources or CSL product information for the species covered by each antivenom product. 2

If indicated, antivenom should be given immediately in sufficient doses to improve coagulation studies. A child should receive the same dose as an adult. 8 Pregnancy is not a contraindication to antivenom therapy. Skin testing before antivenom administration is not routinely recommended. 8 If the type of snake cannot be identified, one or two appropriate monovalent antivenoms, specific for a known group of snakes, may be selected using knowledge of snakes found in the geographic area. Polyvalent antivenom is used in the following circumstances: (1) monovalent antivenom is not available; (2) the SVDK is not available or has failed to identify the type of snake and the range of possible snakes would require the mixing of three or more monovalent antivenoms; (3) the patient is severely envenomated, there is insufficient time to wait for SVDK results, and the range of possible snakes would require the mixing of three or more monovalent antivenoms; or (4) stocks of appropriate monovalent antivenom have been exhausted and the patient requires further antivenom treatment.9

In contrast to experience around the world, anaphylaxis appears to be a rare complication of antivenom therapy in Australia. 814 Nevertheless, patients should be treated in a setting where anaphylaxis can be managed. Premedication with a subcutaneous dose of 0.3 mL of 1:1000 epinephrine (adrenaline) in an adult or 0.1 mL in a child along with a parenteral antihistamine is recommended by some authors.815 Although prospective data are lacking, corticosteroids may have a role in premedication and prevention of serum sickness. Most treatment protocols dictate that patients with a history of allergy to equine proteins should receive corticosteroids. In addition, a 5-day course of prednisolone may be prescribed in an attempt to reduce the incidence of serum sickness in those patients who receive large doses of monovalent antivenom or polyvalent antivenom.8

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