injuries poisoning
Snakebites
Treatment of Snakebites
First aid Supportive care Antivenom Wound care Treatment of snakebites begins immediately, before patients are moved to a medical facility. In the field,patients should move or be moved beyond the snake’s striking distance. They should avoid exertion and be reassured, kept warm, and transported rapidly to the nearest medical facility. A bitten extremity should be wrapped loosely and immobilized in a functional position at about heart level, and all rings, watches, and constrictive clothing should be removed. Pressure immobilization to delay systemic absorption of venom (eg, by wrapping wide crepe or other fabric bandages around the limb) may be appropriate for coral snake bites but is not recommended in the US, where most bites are from pit vipers; pressure immobilization may cause arterial insufficiency and necrosis. First responders should support airway and breathing, administer oxygen, and establish IV access in an unaffected extremity while transporting patients. All other out-of-hospital interventions (eg, tourniquets, topical preparations, any form of wound suction with or without incision, cryotherapy, electrical shock) are of no proven benefit, may be harmful, and may delay appropriate treatment. However, tourniquets that are already placed, unless causing limb-threatening ischemia, should remain in place until patients are transported to the hospital and envenomation is excluded or definitive treatment is initiated. Do not incise or apply tourniquets to snakebite wounds. Serial assessment and testingbegin in the emergency department. Outlining the leading margin of local edema with an indelible marker every 15 to 30 minutes can help clinicians assess progression of local envenomation. Extremity circumference should also be measured on arrival and at regular intervals until local progression subsides. All but trivial pit viper bites require A baseline complete blood count (including platelets) Coagulation profile (eg, prothrombin time, partial thromboplastin time, fibrinogen) Measurement of fibrin degradation products Urinalysis Measurement of serum electrolytes, bloodureanitrogen, and creatinine For moderate and severe envenomations, patients require blood typing and cross-matching, ECG, chest x-ray, and creatine kinase tests, as governed by the patient’s status, often as frequently as every 4 hours for the first 12 hours and then daily. In the management of patients with coral snake bites, neurotoxic venom effects necessitate monitoring of Pulse Oximetry and baseline and serial pulmonary function tests (ie, peak flow, vital capacity). for all patients with pit viper bites should be at least 8 hours. Patients without evidence of envenomation after 8 hours may be sent home after adequate Adjunctive measures . Patients with coral snake bites should be monitored closely for at least 12 hours in case respiratory paralysis develops. Envenomation initially assessed as mild may progress to severe within several hours. . Tracheostomy may be needed if trismus, laryngeal spasm, or excessive salivation is present. Along with aggressive supportive care, antivenom is the mainstay of treatment for patients with anything more than the mildest envenomation grade. For pit viper envenomation, the mainstay of treatment in the US is an ovine-derivedCrotalidae polyvalent immune FAbantivenom (purified FAb fragments of IgG harvested from pit viper venom–immunized sheep). The effectiveness of this antivenom is time and dose related; it is most effective in preventing venom-induced tissue damage when given early. It is less effective if delayed but can reverse coagulopathies and be effective even when started 24 hours after envenomation.Crotalidae polyvalent immune FAbis very safe, although it can still cause acute (cutaneous or anaphylactic) reactions and delayed hypersensitivity reactions (serum sickness). Serum sickness develops in up to 16% of patients 1 to 3 weeks after administration of the FAb product. A loading dose of 4 to 12 vials of reconstitutedCrotalidae polyvalent immune FAbdiluted in 250 mL of normal saline should be infused slowly at 20 to 50 mL/hour for the first 10 minutes; then, if no adverse reactions occur, the remainder is infused over the next hour. The same dose can be repeated 2 times as needed to achieve initial control of symptoms, reverse coagulopathies, and correct physiologic parameters. In children, the dose is not decreased (eg, based on weight or size). Measuring the circumference of the involved extremity at 3 points proximal to the bite and measuring the advancing border of edema every 15 to 30 minutes can guide decisions about the need for additional doses. Once control is achieved, a 2-vial dose in 250 mL saline is given at 6, 12, and 18 hours to prevent recurrence of limb swelling and other venom effects. Crotalidae immune F(ab')2 (equine) is a newly available horse-derived antivenom consisting of reconstituted Crotalidae immune Fab2 fragments and is used to treat North American rattlesnake bites in adults and children. The recommended initial dose is 10 vials diluted in 250 mL of normal saline and infused at 25 to 50 mL/hour for the first 10 minutes, while watching for any evidence of allergic reactions. If no reactions occur, the infusion may proceed at the full rate of 250 mL/hour until completed. This initial dose may be repeated every hour if needed to arrest the progression of symptoms. Late or reemerging symptoms may be treated with additional 4 vial doses. Give children envenomated by a pit viper bite full adult doses of antivenom. Pit viper species may affect dose. Cottonmouth, copperhead, and pygmy rattlesnake envenomations may require smaller doses of antivenom. However, antivenom should not be withheld based on the species of snake and should be given based on envenomation grading regardless of the species. Special attention is warranted for children, older patients, and patients with medical conditions (eg, diabetes mellitus, coronary artery disease) who may be more susceptible to venom effects. Forcoral snake envenomation, equine-derived polyvalent coral snake antivenom is given at a dose of 5 vials for suspected envenomation and an additional 10 to 15 vials if symptoms develop. Dose is similar for adults and children. This dosing recommendation may be reduced during national shortages of coral snake antivenom. should be considered for patients with known hypersensitivity to the specific antivenom being considered, horse or sheep serum, and those with a history of asthma or multiple allergies. In such patients, if the envenomation is considered life or limb threatening, H1 and H2 blockers should be given before antivenom in a critical care setting equipped to treat Anaphylaxis . Early anaphylactoid reactions to antivenom have been noted and usually result from too-rapid infusion; treatment is to temporarily stop the infusion and give Symptoms and Signs may develop, manifesting 7 to 21 days after treatment as fever, rash, malaise, urticaria, arthralgia, and lymphadenopathy. Treatment is H1 blockers and a tapering course of oral corticosteroids. Patients should receive tetanus prophylaxis (toxoid and sometimes Ig) as indicated by their history (see table). Snakebites rarely become infected, and antibiotics are indicated only for patients with clinical evidence of infection. If necessary, options include a 1st-generation cephalosporin (eg, oralcephalexin, IVcefazolin) or a broad-spectrum penicillin (eg, oralamoxicillin/clavulanate, IVampicillin/sulbactam). Subsequent antibiotic choices should be based on culture and sensitivity results from wound cultures. for bites is similar to that for other puncture wounds. The area is cleaned and dressed. For limb bites, the extremity is splinted in a functional position and elevated. Wounds should be examined and cleaned daily and covered with a sterile dressing. Blebs, bloody vesicles, or superficial necrosis should be surgically debrided between days 3 and 10, in stages if needed. Sterile whirlpool sessions may be indicated for wound debridement and physical therapy. Fasciotomy (ie, for Compartment Syndrome ) is rarely indicated and should be considered only when compartment pressure is Regional poison centers and zoosare excellent resources when dealing with snakebites, including those by nonnative snakes. These facilities maintain a list of physicians trained in snake identification and snakebite care as well as the Antivenom Index, published and periodically updated by the American Zoo and Aquarium Association and the American Association of Poison Control Centers. This index catalogs the location and number of vials of antivenom available for all native venomous snakes and most exotic species. A national help line is available at 1-800-222-1222. 