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Snakebites Document Transcript

  • 1. Snake Bites I. Epidemiology: Incidence A. Total: 45,000 snake bites in U.S. per year B. Venomous bites: 8000 in U.S. per year C. Deaths from snake bite in U.S.: 12 or less per year D. Envonomation occurs in 75% of U.S. poisonous snakebites II. Etiology: U.S. Poisonous snakes A. Coral Snakes (Family Elapidae) 1. Nonaggressive snakes of the southern U.S. 2. Transfer venom via chewing instead of injection B. Pit Vipers or Crotalidae (99% U.S. venomous bites) 1. Rattlesnake (Crotalus or Sisturus genera) a. Most common poisonous snake in U.S. b. Potent venom c. Responsible for 95% of deaths (esp. Diamondback) 2. Cottonmouth, water moccasin (Agkistrodon piscivorous) a. Aggressive water snakes in Southeastern U.S. b. Moderately potent venom 3. Copperhead (Agkistrodan contortix) a. Least potent venom III. Signs and Symptoms: Pit Vipers (except Mojave rattler) A. Long movable fangs cause skin puncture marks B. Venom alters Coagulation Factors, tissue necrosis 1. Immediate pain and burning at bite site 2. Within a few minutes redness and swelling develops 3. Bite site develops a purplish discoloration C. Generalized symptoms (Hemotoxic effects) 1. Nausea and Vomiting 2. Dizziness 3. Weakness 4. Sweats and chills 5. Metallic or rubbery taste in mouth
  • 2. D. Systemic complications 1. Disseminated Intravascular Coagulation (DIC) 2. Acute Renal Failure 3. Hypovolemic shock (7% of cases) E. Course 1. Not immediately fatal unless envenomation into vein IV. Signs and Symptoms: Coral Snakes A. Small fixed fangs cause tiny semicircular scratches B. Venom contains a Neurotoxin C. Generalized symptoms may be delayed 1-8 hours 1. Drowsiness, Weakness 2. Paresthesias with numbness at bite site 3. Blurred vision 4. Slurred speech 5. Salivation 6. Seizures D. Systemic complications 1. Paralysis 2. Cardiac arrest or respiratory arrest may occur V. Management: First Aid in field A. Get to a medical facility as soon as possible B. Calm and reassure patient C. Attempt to identify snake type from a distance 1. Do not try to capture the snake for Identification D. Do not leave a patient alone E. Have the patient lie down F. Immobilize bite area below the level of the heart G. Remove jewelry or clothing that tighten with swelling H. Clean the bite area with soap and water 1. Apply antiseptic solution and gauze if available I. Use a venom extractor device within 5 minutes of bite 1. Do not cut wound or try to suck out venom 2. Use vacuum-suction device to extract venom 3. Venom extractor left in place for 30 minutes 4. Avoid harmful methods (see below) at bite site J. Low pressure constriction band 1. Indicated if medical assistance is >1 hour away 2. Wrap a band (ACE, belt, sock) 2-3 inches above bite
  • 3. a. Band should be wide and flat b. Band applied between bite site and heart 3. Do not cut off arterial circulation a. Pressure: 20 mmHg b. Be able to slip a finger between band and skin 4. Leave band in place until medical facility VI. Labs A. Blood Type and cross match B. Urinalysis C. Chemistry panel (e.g. Chem8) 1. Renal Function tests (BUN and Creatinine) 2. Serum electrolytes 3. Serum Glucose D. Liver Function Tests E. Coagulation Factors (draw baseline and at 12 hours) 1. Complete Blood Count with Platelet Count 2. Prothrombin Time (PT) 3. Partial Thromboplastin Time (PTT) 4. Fibrinogen 5. Fibrin Degradation Products F. Other studies that may be indicated 1. Electrocardiogram (EKG) 2. Arterial Blood Gas (ABG) VII. Management: Emergency Department A. See Snake Antivenin B. Contact poison control immediately C. Clean wound D. Tetanus Toxoid or immune globulin if underimmunized E. Do not draw blood or start IV in affected extremity F. Start intravenous fluids G. Prophylactic antibiotics are not recommended H. Suspected pit viper bite management 1. Observe asymptomatic patients 12 hours after bite 2. Mark leading edge of bite site swelling q30 minutes 3. Indications for discharge a. No proximal spread of extremity findings b. Normal laboratory studies c. Patient able to return immediately for worsening
  • 4. I. Suspected coral snake bite management 1. Observe asymptomatic patient for at least 24 hours 2. Requires immediate treatment and antivenin VIII. Avoid harmful methods A. Do not cut skin at bite site B. Fasciotomy is rarely indicated 1. Compartment Syndrome may be controlled by antivenin 2. Only Consider if hourly serial ICP >30 mmHg C. Do not use electric shock or stun gun at bite site D. Do not apply tightly constricting tourniquet E. Do not administer antivenin in the field 1. Risk of Anaphylaxis IX. Prevention A. On coming upon a snake: 1. Slowly and quietly move away, and allow it to escape 2. Do not expect a warning before they strike a. Most snakes do not hiss or rattle before striking 3. Do not handle any snake (even if snake appears dead) B. Be alert in areas commonly inhabited by snakes 1. Hiking, picnicking, camping and firewood areas 2. Water areas 3. Tall grass, underbrush, abandoned buildings 4. Piles of logs, rocks, and branches C. Be careful of areas of decreased visibility 1. Avoid reaching into holes and crevices 2. Avoid jumping over logs and fences 3. Pull logs or rocks toward you when turning over 4. Avoid placing fingers under objects being lifted D. Prepare for a hike 1. Wear boots and long pants 2. Carry a flashlight for nighttime conditions 3. Hike with a companion E. Reduce residential risks of snake bite 1. Provide lighting for yard, sidewalks, and patio 2. Keep yard mowed and bushes pruned 3. Keep home free of mice
  • 5. The Clinical Management of Snake Bites in the South East Asian Region Conclusions and main recommendations It is clear that in many parts of the South East Asian region, snake bite is an important medical emergency and cause of hospital admission. It results in the death or chronic disability of many active younger people, especially those involved in farming and plantation work. However, the true scale of mortality and acute and chronic morbidity from snake bite remains uncertain because of inadequate reporting in almost every part of the region. To remedy this deficiency, it is strongly recommended that snake bite should be made a specific notifiable disease in all countries in the South East Asian region. Snake bite is an occupational disease of farmers, plantation workers, herdsmen, fishermen and other food producers. It is therefore a medical problem that has important implications for the nutrition and economy of the countries where it occurs commonly. It is recommended that snake bite should be formally recognised as an important occupational disease in the South East Asian region. Despite its importance, there have been fewer proper clinical studies of snake bite than of almost any other tropical disease. Snake bites probably cause more deaths in the region than do Entamoeba histolytica infections but only a small fraction of the research investment in amoebiasis has been devoted to the study of snake bite. It is recommended that governments, academic institutions, pharmaceutical, agricultural and other industries and other funding bodies, should actively encourage and sponsor properly designed clinical studies of all aspects of snake bite. Some ministries of health in the region have begun to organise training of doctors and other medical workers in the clinical management of snake bite patients. However, medical personnel
  • 6. throughout the region would benefit from more formal instruction on all aspects of the subject. This should include the identification of medically-important species of snake, clinical diagnosis and the appropriate use of antivenoms and ancillary treatments. It is recommended that education and training on snake bite should be included in the curriculum of medical schools and should be addressed specifically through the organisation of special training courses and other educational events. Community education on snake bite is outside the terms of reference of this publication. However, it is clear that this is an essential component of any community programme for prevention of snake bite. Community education about venomous snakes and snake bite is strongly recommended as the method most likely to succeed in preventing bites. Most of the familiar methods for first-aid treatment of snake bite, both western and quot;traditional/herbalquot;, have been found to result in more harm (risk) than good (benefit). Their use should be discouraged and they should never be allowed to delay the movement of the patient to medical care at the hospital or dispensary. Recommended first-aid methods emphasise reassurance, immobilisation of the bitten limb and movement of the patient to a place where they can receive medical care as soon as possible. Diagnosis of the species of snake responsible for the bite is important for optimal clinical management. This may be achieved by identifying the dead snake or by inference from the quot;clinical syndromequot; of envenoming. A syndromic approach should be developed for diagnosing the species responsible for snake bites in different parts of the region. Antivenom is the only effective antidote for snake venom. However, it is usually expensive and in short supply and its use carries the risk of potentially dangerous reactions. It is recommended that antivenom should be used only in patients in whom the benefits of treatment are considered to exceed the risks. Indications for
  • 7. antivenom include signs of systemic and/or severe local envenoming. Skin/conjunctival hypersensitivity testing does not reliably predict early or late antivenom reactions and is not recommended. It is recommended that whenever possible antivenom should be given by slow intravenous injection or infusion. Epinephrine (adrenaline) should always be drawn up in readiness in case of an early anaphylactic antivenom reaction. Subcutaneous epinephrine (adernaline) may reduce the incidence of early antivenom reactions if given immediately before the start of antivenom treatment. When no antivenom is available judicious conservative treatment can in many cases save the life of the patient. In the case of neurotoxic envenoming with bulbar and respiratory paralysis antivenom alone cannot be relied upon to prevent early death from asphyxiation. Artificial ventilation is essential in such cases. In countries where neurotoxic envenoming is common more doctors should be trained to carry out endotracheal intubation and mechanical ventilators should be available in major hospitals. Conservative management and, in some cases, dialysis, is an effective supportive treatment for acute renal failure in victims of Russell’s viper, saw-scaled viper and sea snake bites. Fasciotomy should not be carried out in snake bite patients unless or until haemostatic abnormalities have been corrected, clinical features of an intracompartmental syndrome are present and a high intracompartmental pressure has been confirmed by direct measurement. Last update: 05 October 2005
  • 8. Venomous Snakebites in the United States: Management Review and Update GREGORY JUCKETT, M.D., M.P.H., and JOHN G. HANCOX, M.D. West Virginia University School of Medicine, Morgantown, West Virginia Venomous snakebites, although uncommon, are a potentially deadly emergency in the United States. Rattlesnakes cause most snakebites and related fatalities. Venomous O A patient infor- snakes in the United States can be classified as having hemotoxic or neurotoxic venom. mation handout on snakebites, written Patients with venomous snakebites present with signs and symptoms ranging from by the authors of fang marks, with or without local pain and swelling, to life-threatening coagulopathy, this article, is pro- renal failure, and shock. First-aid techniques such as arterial tourniquets, application of vided on page 1377. ice, and wound incisions are ineffective and can be harmful; however, suction with a venom extractor within the first five minutes after the bite may be useful. Conserva- tive measures, such as immobilization and lymphatic constriction bands, are now advo- cated until emergency care can be administered. Patients with snakebites should undergo a comprehensive work-up to look for possible hematologic, neurologic, renal, and cardiovascular abnormalities. Equine-derived antivenin is considered the standard of care; however, a promising new treatment is sheep-derived antigen binding frag- ment ovine (CroFab), which is much less allergenic. Although there is no universal grad- ing system for snakebites, a I through IV grading scale is clinically useful as a guide to antivenin administration. Surgical intervention with fasciotomy is now reserved for rare cases. Snakebite prevention should be taught to patients. (Am Fam Physician 2002; 65:1367-74,1377. Copyright© 2002 American Academy of Family Physicians.) E ach year, approximately 8,000 occur between April and October, when out- venomous snakebites occur in the door activities are popular.5 United States.1,2 Between 1960 In the United States, 99 percent of and 1990, no more than 12 fatali- snakebites are caused by the Crotalidae (pit ties from snake venom poisoning viper) family of snakes6 (Table 1). The Crotal- were reported annually.3,4 Most snakebites idae family includes the following snakes: rat- TABLE 1 Venomous Snakes Common in the United States Rattlesnakes Rattlesnakes (continued) Copperheads Coral snakes Banded rock Prairie Broad-banded Arizona Black-tailed Red diamond Northern Eastern Canebrake Ridge-nosed Osage Texas Diamondback (eastern and western) Sidewinder Southern Western Massasauga (eastern and western) Speckled Trans-Pecos Mojave Tiger Cottonmouths Mottled rock Timber Eastern Pacific (northern and southern) Twin-spotted Florida Pigmy (southeastern and western) Western Information from Conant R, Collina JT. A field guide to reptiles & amphibians: eastern and central North America. 3d ed. Boston: Houghton Mifflin, 1998, and Stebbins RC. A field guide to western reptiles and amphibians: field marks of all species in western North America, including Baja California. 2d ed. Boston: Houghton Mifflin, 1998. APRIL 1, 2002 / VOLUME 65, NUMBER 7 www.aafp.org/afp AMERICAN FAMILY PHYSICIAN 1367
  • 9. FIGURE 1. Rattlesnake tail. The rattle is the FIGURE 3. Cottonmouth or water moccasin hallmark of Crotalus and Sistrurus genera of (Agkistrodon piscivorous). the Crotalidae (“pit viper”) family of snakes. FIGURE 2. Copperhead snake (Agkistrodon contortrix). tlesnakes, genera Crotalus and Sistrurus (Fig- ure 1); copperheads, Agkistrodon contortrix (Figure 2); and cottonmouths, or water moc- casins, Agkistrodon piscivorous (Figure 3). These snakes are referred to as pit vipers because of small, heat-sensitive pits between the eye and the nostril that allow them to sense their prey. Because of their widespread distribution and relatively potent venom, rattlesnakes are FIGURE 5. Coral snakes (Micrurus species) are responsible for the majority of fatalities from a less common cause of snakebites in the United States. snakebites; eastern and western varieties of diamondback rattlesnakes account for almost 95 percent of these deaths.3 Bites the family elapidae (Figure 5) are responsible from copperhead snakes, which are common for a minority of snakebites in the United in the eastern United States, seldom require States. Native to the deep South, their terri- antivenin therapy because they have the least tory extends west to Arizona. Coral snakes are potent venom and a negligible fatality rate. secretive and nonaggressive; they seldom bite Cottonmouths, or water moccasins, are unless provoked. Their venom is transferred aggressive semi-aquatic snakes native to the by chewing rather than by injecting. Coral southeast; they have an intermediate-potency snake bites, although rare, are easy to miss, venom. Coral snakes of the Micrurus genus in and often present as painless, tiny puncture 1368 AMERICAN FAMILY PHYSICIAN www.aafp.org/afp VOLUME 65, NUMBER 7 / APRIL 1, 2002
  • 10. Snakebites wounds with negligible surrounding tissue change. Because of their widespread distribution and relatively potent Although exotic snakes account for only a venom, rattlesnakes are responsible for most fatalities from small percentage of venomous snakebites,7 snakebites in the United States. the prevalence of these bites is increasing as the popularity of keeping exotic snakes as house pets continues to rise. lation, acute renal failure, hypovolemic shock, Snake Envenomation and death. Renal failure is a common cause of Snake venoms can be classified as hemo- delayed mortality from untreated snakebites toxic (attacking tissue and blood) and neuro- in developing parts of the world. Immediately toxic (damaging or destroying nerve tissue). life-threatening conditions such as hypoten- Pit viper snake venoms are hemotoxic, except sion or shock occur in only about 7 percent of for some Mojave rattlers. Contrary to public envenomations.7 perception, pit viper bites are not immedi- The venoms of coral snakes, exotic elapids ately fatal unless the venom enters a vein and some Mojave rattlesnakes are neurotoxic directly. The venom consists of proteins, and usually cause local numbness instead of polypeptides, and enzymes that cause necro- pain and swelling, with the risk of cranial sis and hemolysis. Most crotalid venoms nerve palsies, respiratory paralysis, and death. damage capillary endothelial cells, resulting Symptoms of neurotoxic envenomations are in third spacing of plasma and extravasation listed in Table 2. Systemic reactions are diffi- of erythrocytes.8 cult to reverse once they develop. Pit viper bites classically appear as two fang punctures (one or three puncture wounds Snakebite First Aid occur, but rarely) with local swelling and In recent years, first aid measures for necrosis. Extremity bites are rarely compli- snakebites have been radically revised to cated by infection and compartment syn- exclude methods that were found to worsen a drome, and prophylactic fasciotomies often patient’s condition, such as tight (arterial) do more harm than good. Clinical effects of snakebites range from mild local reactions to life-threatening sys- TABLE 2 temic reactions, depending on the species and Symptoms of Snakebite Envenomation size of the snake involved; the location of the bite(s); the volume of venom injected; and Hemotoxic symptoms Neurotoxic symptoms the age, size, and health of the victim. Chil- Intense pain Minimal pain dren are more likely to suffer significant mor- Edema Ptosis bidity and mortality because they receive a Weakness Weakness Swelling Paresthesia (often numb larger envenomation relative to body size.9 Numbness or tingling at bite site) Most pit viper bites are painful within five Rapid pulse Diplopia minutes and soon display local swelling. Ecchymoses Dysphagia Symptoms of hemotoxic envenomation are Muscle fasciculation Sweating listed in Table 2. Significant hypofibrinogen- Paresthesia (oral) Salivation emia and thrombocytopenia lasting up to two Unusual metallic taste Diaphoresis weeks may occur after envenomation by Vomiting Hyporeflexia North American pit vipers.10 Confusion Respiratory depression Systemic reactions include a syndrome Bleeding disorders Paralysis similar to disseminated intravascular coagu- APRIL 1, 2002 / VOLUME 65, NUMBER 7 www.aafp.org/afp AMERICAN FAMILY PHYSICIAN 1369
  • 11. left in place for 30 minutes.5 Although electric First-aid measures for snakebite include avoiding excessive shock (often with a stun gun) has been a activity, immobilizing the bitten extremity, and quickly trans- popular treatment for snakebite in develop- ing countries, it should be avoided as it is a porting the victim to the nearest hospital. potentially hazardous intervention that has never been shown to be effective.14 An attempt should be made to identify the tourniquets, aggressive wound incisions, and type of snake from a safe distance; however, ice. Initial treatment measures should include no attempt should be made to capture or kill avoiding excessive activity, immobilizing the the snake. Even if the snake is dead, it should bitten extremity, and quickly transporting the not be picked up with the hands because victim to the nearest hospital.11 envenomation by reflex biting after death of A wide, flat constriction band may be the snake has been reported.15 applied proximal to the bite to block only Equine-derived antivenin to snake venom superficial venous and lymphatic flow (typi- is not recommended for the formularies of cally, with about 20 mm Hg pressure) and standard emergency medical services because should be left in place until antivenin therapy, of the potential for life-threatening allergic if indicated, is begun. One or two fingers reactions from the antivenin and the length of should easily slide beneath this band, since any time required for reconstitution (up to impairment of arterial blood flow could 60 minutes).16 As safer products, such as Cro- increase tissue death. Upper extremities talidae Polyvalent Immune Fab (Ovine; Cro- should be splinted as close to a gravity-neutral Fab), become more commonplace, antivenin position as possible, preferably at heart level. administration in the field may become more No study has shown any benefit in survival feasible, especially in remote areas. or outcome from incision and suction.11-13 However, a venom extractor can be beneficial Treatment if applied within five minutes of the bite and Patients with snakebite must be admitted to an emergency department, where a poison control center should be contacted immedi- TABLE 3 ately. Wounds should be cleaned, and admin- Laboratory Evaluation in Snakebite istration of tetanus toxoid or tetanus immune globulin should be considered for under- Complete blood count with platelets Platelet count immunized or nonimmunized patients. Pa- and differential* Liver function tests tients should be given intravenous fluid, and Prothrombin time* Bilirubin blood should be drawn from an unaffected Partial thromboplastin time* Creatine kinase extremity. Complete recommendations for Fibrinogen* Creatinine Fibrin degradation products* Urinalysis† laboratory evaluations of snakebite are sum- Blood type and cross match Stool hemoccult marized in Table 3. At least 25 percent of Serum electrolytes Electrocardiography‡ snakebites do not result in envenomation. Glucose Arterial blood gas§ Patients with asymptomatic pit viper bites Blood urea nitrogen should be observed for at least 12 hours before discharge.8 When envenomation does occur, *—Should be performed as soon as possible and repeated within 12 hours. the leading edge of the swelling should be †—Including free protein, hemoglobin, and myoglobin. ‡—Suggested for patients older than 50 years and patients with a history of marked, the time of observation recorded, and heart disease.11 the circumference of the extremity measured §—Should be tested if any signs or symptoms of respiratory compromise are evident. every 30 minutes.17 If there is no proximal progression of local signs on the extremity 1370 AMERICAN FAMILY PHYSICIAN www.aafp.org/afp VOLUME 65, NUMBER 7 / APRIL 1, 2002
  • 12. Snakebites and no coagulopathy after 12 hours of clinical observation and serial laboratory examina- Equine-derived antivenin to snake venom has been the main- tions, a reliable patient can be sent home. stay of hospital treatment for venomous snakebites. The patient should be given strict instruc- tions to return to the hospital immediately if any of the following occurs: increase in pain or onset of redness or swelling; fever; epi- bites in October 2000; its use is still limited staxis; bloody or dark urine; nausea or vomit- because of availability and expense, but it is ing; faintness; shortness of breath; diaphore- likely to soon replace the equine crotalid sis; or other symptoms except mild pain at the antivenin. A prospective trial using CroFab bite site.8 Prophylactic antibiotics are usually reports only a 14.3 percent incidence of acute not recommended, as the occurrence of reaction, and nearly all events were mild to wound infection following crotalid enveno- moderate.20 Experience with CroFab is still mation is low (3 percent).18,19 too limited to support the conclusion that Patients with bites from snakes with neuro- serious allergic reactions like anaphylaxis will toxic venom should be observed for at least never occur with its administration. 24 hours. A patient with suspected enveno- Eastern coral snakebites require Antivenin mation by the eastern coral snake needs (Micrurus fulvius). The specific antivenin for immediate treatment with an appropriate exotic snakebites may be acquired from the antivenin, and necessary resuscitation mea- Arizona Poison and Drug Information Center sures should be implemented. (520-626-6016). An antivenin index is avail- able from the American Zoo and Aquarium Antivenin Indications and Administration Association (301-562-0777) and the American Equine-derived antivenin to snake venom Association of Poison Control Centers (800- has been the mainstay of hospital treatment 222-1222).22 A prescription is required to for venomous snakebite for 35 years.20 It is obtain U.S. antivenin, and a permit is needed used to treat approximately 75 percent of the to import antivenin not held domestically.23 venomous snakebites inflicted annually in the Ideally, antivenin is administered within United States.5 The majority of snakebite vic- four hours of the snakebite, but it is effective tims in the United States reach a medical for at least the first 24 hours. Physicians facility within 30 minutes to two hours of should be present for antivenin administra- being bitten and can be given antivenin at an tion, and epinephrine and antihistamines early stage.3 (both histamine H1 and H2 receptor blockers) For rattlesnake, cottonmouth, and copper- should be at the bedside. head bites, Antivenin (Crotalidae) Polyvalent Performing a skin test with horse serum is a (ACP) has been the standard available treat- matter of controversy because it delays ther- ment; however, ACP is known to be highly apy, has itself caused anaphylaxis and serum allergenic because of its equine origin and sickness,24,25 and has been demonstrated to may pose a greater risk to the patient than the have a 10 to 36 percent false-negative rate21,26 snakebite.21 In retrospective studies,20 rates for and a 33 percent false-positive rate.21 Some acute allergic reactions (including hypoten- physicians believe that medicolegal issues sion and anaphylaxis) after ACP administra- mandate that this test be performed before tion range from 23 to 56 percent, with even antivenin administration except in extreme higher rates for delayed serum sickness. emergencies.27 Other physicians bypass skin The ovine (sheep-derived) antivenin, Cro- testing altogether, relying instead on premed- Fab, received approval by the U.S. Food and ication with antihistamines and a trial dose of Drug Administration for treatment of snake- 5 mL of antivenin administered intravenously. APRIL 1, 2002 / VOLUME 65, NUMBER 7 www.aafp.org/afp AMERICAN FAMILY PHYSICIAN 1371
  • 13. In the event of a significant skin-test reac- administration. Reconstitution can take up to tion, antivenin would be reserved for use in 60 minutes and should be initiated immedi- only the most severe cases and should only be ately when the patient arrives in the emer- given with careful monitoring, hydration, and gency department. ACP can be reconstituted premedication with antihistamines.An alterna- by injecting 10 mL of supplied sterile water tive to skin testing is to premedicate all patients diluent into each vial and swirling (not shak- who will receive equine antivenin.28 Suggested ing) to mix, or by diluting 10 vials of antivenin intravenous antihistamine pretreatment is in 1 L of normal saline. The reconstituted diphenhydramine (Benadryl), in a dosage of 1 antivenin (amount will vary, depending on mg per kg, and cimetidine (Tagamet), in a amount required) is then diluted in 500 mL of dosage of 6 mg per kg.8 If signs or symptoms of normal saline or 5 percent dextrose in water, anaphylaxis develop, the patient should be and a trial dose of 5 to 10 mL is administered immediately treated with epinephrine and intravenously over five minutes. If no reaction steroids.8 Unstable patients (i.e., those with occurs, the rate should be adjusted to give up hypotension, severe coagulopathy, respiratory to 10 vials in the first hour. Additional infu- distress) must receive antivenin because no sions should be given every two hours until other treatment can reverse the venom’s effect. signs and symptoms are resolving. The unpredictable nature of snakebites In contrast, the safer CroFab is given as a often makes assessment and management large initial dose to control the envenoma- difficult. Progressive local injury (swelling, tion, and smaller subsequent doses are given ecchymosis), a clinically evident coagulation as needed. In one study,20 a total of three to 12 abnormality, or systemic effects (hypoten- vials of CroFab were given for initial control, sion, altered mental status) are strong indica- and additional two-vial doses were given at tions for antivenin treatment. Withholding six, 12, and 18 hours. antivenin is recommended in patients with For any eastern coral snake bite with possi- milder envenomations.21 The decision to use ble envenomation, three to five vials of antivenin requires a careful analysis of the Antivenin (Micrurus fulvius) should be risks and benefits. administered immediately. If systemic mani- festations are present, at least six to 10 vials ADMINISTRATION OF ANTIVENIN should be administered. One exception is the Both ACP and CroFab are provided as dry Arizona coral snake (Micruroides), which is powders and require reconstitution before not associated with human fatality and for which no antivenin exists. Immediate hypersensitivity reactions to any antivenin should be managed with epi- The Authors nephrine, antihistamines and supportive care GREGORY JUCKETT, M.D., M.P.H., is associate professor in the Department of Family to protect the respiratory and cardiovascular Medicine at West Virginia University School of Medicine, Morgantown. He received a systems. Serum sickness, which commonly medical degree from Pennsylvania State University College of Medicine, Hershey, and a master’s degree in public health from West Virginia University. He completed a family occurs one to four weeks after administration medicine residency at the Medical University of South Carolina, Charleston. Dr. Juckett of antivenin, presents with pruritus, urticaria, is a diplomate in tropical medicine of the American Society of Tropical Medicine and fever, and arthralgias. Serum sickness can be Hygiene and coordinates the International Travel Clinic at West Virginia University. successfully treated with systemic steroids. JOHN G. HANCOX, M.D., is an intern in internal medicine and psychiatry at West Vir- ginia University School of Medicine, where he received his medical degree. He will begin GRADING THE SEVERITY OF THE BITE a dermatology residency at Wake Forest University, Winston-Salem, N.C., in July 2002. A popular scale for grading the severity of Address correspondence to Gregory Juckett, M.D., M.P.H., West Virginia University School of Medicine, Robert C. Byrd Health Sciences Center, Morgantown, WV 26506 pit viper bites and estimating the antivenin (e-mail: gjuckett@hsc.wvu.edu). Reprints are not available from the authors. dose is presented in Table 4. It is important to 1372 AMERICAN FAMILY PHYSICIAN www.aafp.org/afp VOLUME 65, NUMBER 7 / APRIL 1, 2002
  • 14. Snakebites TABLE 4 Grading Scale for Severity of Snake Bites Degree of envenomation Presentation Treatment 0. None Punctures or abrasions; some pain or tenderness Local wound care, no antivenin at the bite I. Mild Pain, tenderness, edema at the bite; perioral If antivenin is necessary, administer paresthesias may be present. about five vials.* II. Moderate Pain, tenderness, erythema, edema beyond the Administration of five to 15 vials area adjacent to the bite; often, systemic of antivenin may be necessary. manifestations and mild coagulopathy III. Severe Intense pain and swelling of entire extremity, Administer at least 15 to 20 vials often with severe systemic signs and symptoms; of antivenin. coagulopathy IV. Life-threatening Marked abnormal signs and symptoms; severe Administer at least 25 vials of coagulopathy antivenin. *—Because of their less potent venom, grade-I copperhead bites are usually not treated with antivenin. remember that a patient must have serial measured compartment pressures exceeding evaluations, because an envenomation that 30 mm Hg. These criteria should be present appears to be mild on presentation can soon despite elevation of the affected limb and exhibit the hallmarks of a severe envenoma- administration of 20 vials of antivenin.8 In an tion. Doses of antivenin must not be reduced animal study,29 the best outcome in subjects for children or small persons, since the with compartment syndrome was achieved amount of venom that needs to be neutral- with the administration of antivenin alone. In ized is the same. a series of 1,257 cases of extremity bites, only two fasciotomies were necessary.12 Surgical Management Although once popular, surgical interven- Prevention tion with fasciotomy for venomous snakebite Physicians should educate their patients on is now reserved for selected rare cases and ways to prevent snakebites, as prevention is should never be performed prophylactically. far preferable to treatment. Many bites can be The local and systemic effects of crotaline easily prevented by using common sense. For venom closely resemble the signs and symp- some precautions against snakebites, see the toms of compartment syndrome15 and can- accompanying patient information handout on not be reliably diagnosed in an envenomated page 1377. patient without directly measuring the com- partment pressure. The photographs in Figures 1 through 4 were pro- vided by James G. Arbogast, M.D., West Virginia Uni- Fasciotomy should only be performed in versity School of Medicine, and John N. Casto, M.D. patients with clinical signs and symptoms of is in private practice in Ridgely, WV. compartment syndrome (i.e., pain on passive stretch, hypoesthesia, tenseness of compart- The authors indicate that they do not have any con- ment, and weakness) and hourly, serially flicts of interest. Sources of funding: none reported. APRIL 1, 2002 / VOLUME 65, NUMBER 7 www.aafp.org/afp AMERICAN FAMILY PHYSICIAN 1373
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