Sunday, May 14, 2017

A Brief Discussion on Snakebites (Poisonous)

Poisonous snakebites
are most common during summer afternoons in grassy or rocky habitats. Poisonous snakebites are medical emergencies. With prompt, correct treatment, they need not be fatal.

The only poisonous snakes in the United States are pit vipers (Crotalidae) and coral snakes (Elapidae). Pit vipers include rattlesnakes, water moccasins (cottonmouths), and copperheads. They have a pitted depression between their eyes and nostrils and two fangs, ¾? to 1¼? (2 to 3 cm) long. Because fangs may break off or grow behind old ones, some snakes may have one, three, or four fangs.
Because coral snakes are nocturnal and placid, their bites are less common than pit viper bites; pit vipers are also nocturnal but are more active. The fangs of coral snakes are short but have teeth behind them. Coral snakes have distinctive red, black, and yellow bands (yellow bands always border red ones), tend to bite with a chewing motion, and may leave multiple fang marks, small lacerations, and much tissue destruction.

Signs and symptoms
Most snakebites happen on the arms and legs, below the elbow or knee. Bites to the head or trunk are most dangerous, but any bite into a blood vessel is dangerous, regardless of location.

Most pit viper bites that result in envenomation cause immediate and progressively severe pain and edema (the entire extremity may swell within a few hours), local elevation in skin temperature, fever, skin discoloration, petechiae, ecchymoses, blebs, blisters, bloody wound discharge, and local necrosis.
Because pit viper venom is neurotoxic, pit viper bites may cause local and facial numbness and tingling, fasciculation and twitching of skeletal muscles, seizures (especially in children), extreme anxiety, difficulty speaking, fainting, weakness, dizziness, excessive sweating, occasional paralysis, mild to severe respiratory distress, headache, blurred vision, marked thirst and, in severe envenomation, coma and death. Pit viper venom may also impair coagulation and cause hema-temesis, hematuria, melena, bleeding gums, and internal bleeding. Other symptoms of pit viper bites include tachycardia, lymphadenopathy, nausea, vomiting, diarrhea, hypotension, and shock.
The reaction to coral snakebite is usually delayed—sometimes up to several hours. These snakebites cause little or no local tissue reaction (local pain, swelling, or necrosis). However, because coral snake venom is neurotoxic, a reaction can progress swiftly, producing such effects as local paresthesia, drowsiness, nausea, vomiting, difficulty swallowing, marked salivation, dysphonia, ptosis, blurred vision, miosis, respiratory distress and possible respiratory failure, loss of muscle coordination and, possibly, shock with cardiovascular collapse and death.

The patient’s history and account of the injury, observation of fang marks, snake identification (when possible), and progressive symptoms of envenomation all point to poisonous snakebite. Laboratory test results help identify the extent of envenomation and provide guidelines for supportive treatment.
Abnormal test results in poisonous snakebites may include the following:
  • prolonged bleeding time and partial thromboplastin time
  • decreased hemoglobin and hematocrit values
  • sharply decreased platelet count (less than 200,000/┬Ál)
  • urinalysis disclosing hematuria
  • increased white blood cell count in victims who develop an infection (the mouth of a snake typically contains gram-negative bacteria)
  • pulmonary edema as shown on chest X-ray
  • possibly tachycardia and ectopic heartbeats on the electrocardiogram (usually necessary only in cases of severe envenomation for a patient older than age 40)
  • possibly abnormal EEG findings in cases of severe envenomation.
Prompt, appropriate first aid can reduce venom absorption and prevent severe symptoms.
If possible, identify the snake, but don’t waste time trying to find it.
Place the victim in the supine position to slow venom metabolism and absorption.
Don’t give the victim any food, beverage, or medication orally.
Authorities disagree about what constitutes appropriate prehospital care. Some recommend against placing a constrictive tourniquet (band) on the affected limb unless the victim is far from a medical facility.
Whether you apply a tourniquet or not, immediately immobilize the victim’s affected limb below heart level, and instruct the victim to remain as quiet as possible.
If a tourniquet is applied, the victim or the person applying the tourniquet should check the victim’s distal pulses regularly and loosen the tourniquet slightly as needed to maintain circulation.
When indicated, apply the tourniquet so that it’s slightly constrictive, obstructing only lymphatic and superficial venous blood flow. Apply the band about 4? (10 cm) above the fang marks or just above the first joint proximal to the bite. The tourniquet should be loose enough to allow a finger between the band and the skin. After the tourniquet is in place, don’t remove it until the victim is examined by a physician.
Caution: Don’t apply a tourniquet if more than 30 minutes has elapsed since the bite. Keep in mind also that total tourniquet time shouldn’t exceed 2 hours and that the use of a tourniquet shouldn’t delay antivenin administration. Remember: Loss of a limb is possible if a tourniquet is too tight or if tourniquet time is too long.
If the patient is more than 30 minutes away from a facility, wash the skin over the fang marks. Within 1 hour of a pit viper bite, make an incision through the fang marks about ½? (1.3 cm) long and 1/8? (0.3 cm) deep. Be especially careful if the bite is on the hand, where blood vessels and tendons are close to the skin surface.
Using a bulb syringe—or, if no other means is available, mouth suction—apply suction for up to 2 hours in the absence of antivenin administration.
Remember: An incision and suction are effective only in pit viper bites and only within 1 hour of the bite and if transport time to an emergency facility would exceed 30 minutes. Mouth suction is contraindicated if the rescuer has oral ulcers, if the victim is close to a medical facility, or if antivenin can be given promptly.
Never give the victim alcoholic drinks or stimulants because they speed venom absorption. Never apply ice to a snakebite because it will increase tissue damage.
Record the signs and symptoms of progressive envenomation and when they develop. Most snakebite victims are hospitalized for only 24 to 48 hours. Treatment usually consists of antivenin administration, but minor snakebites may not require antivenin. Other treatments include tetanus toxoid or tetanus immune globulin; various broad-spectrum antibiotics; and, depending on respiratory status, severity of pain, and the type of snakebite, acetaminophen, codeine, morphine, or meperidine. (Opioids are contraindicated in coral snakebites.)
Necrotic snakebites usually need surgical debridement after 3 to 4 days. Intense, rapidly progressive edema requires fasciotomy within 2 to 3 hours of the bite; extreme envenomation may require amputation of the limb and subsequent reconstructive surgery, rehabilitation, and physical therapy.

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