Snakebite Envenomation

When reaching under a shed for the frog she had been chasing, a 4-year-old girl was bitten by “something.” The parents thought the bite was from a snake because of reports of copperhead sightings in the area. The mother immediately brought the child to the emergency department (ED).

The patient’s vital signs were stable. Her right arm was markedly swollen with multiple ecchymoses up to the proximal elbow. She had 2 puncture wounds on her right hand at the base of the metacarpal joints of the third and fourth digits. Pulses and range of motion were intact. Moving the fingers and wrist caused extreme discomfort. Remaining physical findings, radiographs of the hand and arm, and results of a snakebite laboratory evaluation were all normal.

The patient was treated with CroFab (Crotalidae Polyvalent Immune Fab [ovine])-a total of 7 vials of antivenin. She was also given morphine and acetaminophen for pain and ondansetron for nausea. Within 24 hours, her symptoms had markedly decreased; she was discharged the following day.

About half of all snakebites occur in children, although there is a high prevalence in young men between the ages of 17 and 27 years.^1,2 About 98% of bites occur on the extremities, especially on the hands and arms.^1,2 Roughly 95% of all venomous snakebites in the United States are from crotalids (pit vipers-such as rattlesnakes, copperheads, and cottonmouths); only a few are from elapids (coral snakes).^3,4 Reactions range from mild and localized-as in this patient-to life-threatening and, in rare instances, even fatal. Children often have a more severe clinical course because of their small body size relative to a large venom load.¹ Signs and symptoms of envenomation include immediate pain, swelling, edema, erythema, and ecchymosis.^1,5 Nausea, vomiting, paresthesias, lethargy, numbness/tingling, and weakness may develop.

Patients may also describe a metallic, minty, or rubbery taste.¹ With severe envenomation, hypotension, tachypnea, tachycardia, disseminated intravascular coagulation, and shock may occur.¹ Bites from coral snakes are known to be extremely neurotoxic; although systemic symptoms may take 12 hours to develop, once neurological symptoms begin, respiratory distress rapidly develops.^1,3 After the patient is stable, initial management involves cleaning and examining the wound to determine whether antivenin is necessary, and laboratory testing (including a complete blood cell count with platelets and differential, prothrombin time, partial thromboplastin time, international normalized ratio [INR], fibrinogen, fibrin degradation products, serum electrolytes, blood urea nitrogen, serum creatinine, and urinalysis). Consultation with a specialist who has experience treating snakebites can help avoid unnecessary fasciotomy. A local poison control center should have the latest guidelines for treating envenomations.

The most common indications for antivenin administration include:

• Progressive pain, swelling, and ecchymosis.

• Clinically evident coagulation abnormality (thrombocytopenia, hypoprothrombinemia, or prolonged INR).

• Systemic effects (hypotension, altered mental status).^1,6

There are 2 types of antivenin available in the United States for the treatment of crotalid snakebites. Both are products of animal serum, which can cause anaphylaxis and serum sickness; thus, close monitoring of patients given antivenin is warranted. Circumferential measurements of the wound at timely intervals after the initial dose can be used as a guide for further antivenin administration.^1,3,5 Additional laboratory testing (eg, creatine kinase, blood type and cross-match), a chest radiograph, ECG, and tetanus vaccination may be indicated on the basis of the envenomation severity or patient’s medical history.^1,3,5

Because symptoms may manifest hours after the envenomation, patients should be observed in the ED for a minimum of 8 hours before discharge.¹ Because some misconceptions about the initial care of snakebites persist, a brief review for patients and parents might help. The Box provides a list of do’s and don’ts of snakebite first aid.

References:

REFERENCES:1. Gold BS, Dart RC, Barish RA. Bites of venomoussnakes. N Engl J Med. 2002;347:347-356.

2. Parrish HM, Goldner JC, Silberg SL. Comparison between snakebites in children and adults. Pediatrics. 1965;36:251-256.

3. Bond GR. Snake, spider, and scorpion envenomation in North America. Pediatr Rev. 1999;20:147-151.

4. Corey GR, Armitage JO, Seifert SA. Venomous snake bites. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia: Saunders; 2007: chap 381.

5. Gold BS, Wingert WA. Snake venom poisoning in the United States: a review of therapeutic practice. South Med J. 1994;87:579-589.

6. Dart RC, McNally J. Efficacy, safety, and use of snake antivenoms in the United States. Ann Emerg Med. 2001;37:181-188.