Snake bites
Snakes bite for two reasons: to capture prey or
when they feel threatened, for self-defense. Thus, humans are bitten when the snake feels threatened because they have closely approached it, or accidentally stepped on it. The severity of a snake bite varies
because there are so many different types of snakes, including both venomous
and non-venomous. The severity also varies in cases of the same snake species, depending on the quantity of venom injected and the body size of the victim.
Types of snake bites
There are two types of snake bites:Dry bites: These occur when no venom is released from the snake, usually in the case of non-venomous snakes. In some cases, even a venomous snake species may not release venom upon biting. Non-poisonous bites should be cleaned, the patient should receive anti-tetanus prophylaxis if needed and prophylactic antibiotics as for animal bites. If there are no systemic effects or significant local findings the patient can be discharged home with close observation.
Venomous bites: These occur when a snake transmits venom with its bite. They are much more dangerous than dry bites. The patient should be admitted to the hospital.
Bites from venomous snakes can result in paralysis, bleeding, long-term disability, or death.
Venomous snakes usually have a triangular-shaped head and elliptical pupils whereas nonvenomous snakes usually have a more rounded head and round pupils.
Groups of venomous snakes and clinical manifestations of snake bites
There are two major groups of venomous snakes:Elapids (Elapidae-cobra family): This family includes about 300 venomous species, such as kraits, mambas, coral snakes and sea snakes. Their venom is mainly neurotoxic but it can also cause tissue damage or damage to blood cells.
Often local signs at the site of the bite are minimal and elapid venom systemic effects may develop hours after a bite and are not
easily reversed. Thus, 3-5 vials of IV antivenom should be administered early to patients who have definitely been bitten by such snakes, because it may not be possible to reverse venom effects once they develop.
Frequently the first sign of envenomation is ptosis of the
eyelids. Other manifestations include diplopia, slurred speech, dysphagia, headache, nausea, abdominal pain, progressive generalized muscular weakness,
fasciculations, and seizures. In the case of weakness or
paralysis of the respiratory muscles, death may occur. Thus, the patient should be observed closely for signs of respiratory muscle weakness and hypoventilation.
Vipers: This family includes more than 200 species of
Viperidae snakes, such as pit vipers (like rattlesnakes, cottonmouths, copperheads, and water moccasins) and Old-World vipers (adders, e.g the common European adder,
the puff adder, etc.).
Local symptoms and signs: Pain (often severe), numbness, severe edema (swelling), skin color change, bruising (ecchymosis), bullae, and in some severe cases compartment syndrome. Often one can discern two small holes in the skin. Oozing of blood from the wound suggests envenomation.
Systemic manifestations: Headache, dizziness, nausea and vomiting, abdominal pain, diarrhea, sweating, tachycardia, hypotension, bleeding. Shock may occur due to bleeding and disruption of fluid balance. Bleeding may occur due to venom-induced coagulopathy.
Dyspnea may occur in severe cases due to ARDS (acute respiratory distress syndrome) and renal failure due to myoglobinuria (resulting from muscle damage) and shock (causing decreased renal perfusion).
Local symptoms and signs: Pain (often severe), numbness, severe edema (swelling), skin color change, bruising (ecchymosis), bullae, and in some severe cases compartment syndrome. Often one can discern two small holes in the skin. Oozing of blood from the wound suggests envenomation.
Systemic manifestations: Headache, dizziness, nausea and vomiting, abdominal pain, diarrhea, sweating, tachycardia, hypotension, bleeding. Shock may occur due to bleeding and disruption of fluid balance. Bleeding may occur due to venom-induced coagulopathy.
Dyspnea may occur in severe cases due to ARDS (acute respiratory distress syndrome) and renal failure due to myoglobinuria (resulting from muscle damage) and shock (causing decreased renal perfusion).
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| Viper bite |
https://commons.wikimedia.org/wiki/File:Viper_bite.jpg
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Brandenberger
Rosalba, CC BY-SA 3.0 <http://creativecommons.org/licenses/by-sa/3.0/>,
via Wikimedia Commons |
Treatment of snake bites
General measures
If possible, the type of snake should be identified to
determine if a venomous snake is responsible for the bite and the type of venom
injected.
Promptly immobilize the bitten limb and calm the patient. The patient should also be immobilized (e.g. transported lying on a stretcher), if possible. These actions reduce the spread of venom inside the body. The patient should be transported quickly to a medical facility. Tourniquets are not recommended, because they can cause limb ischemia, increase local tissue damage, and also because when the tourniquet is released an abrupt spread of a large quantity of venom will rapidly follow. The use of ice, incision, and suction at the bite site is also not recommended.
Assess vital parameters (heart rate, blood pressure, respiratory rate, pulse oximetry, temperature). In an unstable patient with signs of bleeding, shock, paralysis, or respiratory distress resuscitation measures should be promptly initiated. If hypotension or shock is present initiate intravenous fluids, such as Lactated Ringers or Normal Saline. In the case of respiratory paralysis, the patient is treated with endotracheal intubation and mechanical ventilation.
The site of injury should be cleansed with soap and water and debrided. The skin is marked to identify the rate of spread of edema and erythema. Close observation for the development of compartment syndrome is also required.
Tetanus toxoid should be administered as needed, depending on the patient's immunization status. Prophylactic broad-spectrum antibiotics are administered. Although some authorities also recommend high-dose hydrocortisone and antihistamine to reduce local inflammation and systemic symptoms, most experts do not recommend this treatment and use it only in case of an allergic reaction.
Promptly immobilize the bitten limb and calm the patient. The patient should also be immobilized (e.g. transported lying on a stretcher), if possible. These actions reduce the spread of venom inside the body. The patient should be transported quickly to a medical facility. Tourniquets are not recommended, because they can cause limb ischemia, increase local tissue damage, and also because when the tourniquet is released an abrupt spread of a large quantity of venom will rapidly follow. The use of ice, incision, and suction at the bite site is also not recommended.
Assess vital parameters (heart rate, blood pressure, respiratory rate, pulse oximetry, temperature). In an unstable patient with signs of bleeding, shock, paralysis, or respiratory distress resuscitation measures should be promptly initiated. If hypotension or shock is present initiate intravenous fluids, such as Lactated Ringers or Normal Saline. In the case of respiratory paralysis, the patient is treated with endotracheal intubation and mechanical ventilation.
The site of injury should be cleansed with soap and water and debrided. The skin is marked to identify the rate of spread of edema and erythema. Close observation for the development of compartment syndrome is also required.
Tetanus toxoid should be administered as needed, depending on the patient's immunization status. Prophylactic broad-spectrum antibiotics are administered. Although some authorities also recommend high-dose hydrocortisone and antihistamine to reduce local inflammation and systemic symptoms, most experts do not recommend this treatment and use it only in case of an allergic reaction.
Antivenom
Intravenous antivenom is recommended in patients with systemic symptoms or abnormal laboratory tests, or rapid swelling, or severe local manifestations. Antivenom is the only effective treatment of severe local, or systemic manifestations or hematologic complications. The type and dose of antivenom depend on the likely snake species and local guidelines.Antivenoms are created by immunizing
horses or sheep with the venom of a particular snake. Their blood serum is then
processed, as it will contain antibodies capable of neutralizing the effects of the venom. There are monospecific antivenoms for the treatment of bites from a
specific type of snake and also polyspecific antivenoms which can be used for
the treatment of bites from a number of snakes found in a particular geographic
region.
The antivenom is administered intravenously (IV) and the dosage depends on envenomation severity and not on the body weight or age of the patient. The antivenom should be administered according to the instructions in the package insert.
Antivenom in some cases can cause an allergic reaction that may range from mild urticaria to severe anaphylaxis. With modern antivenoms, acute severe allergic reactions are relatively rare. If an acute allergic reaction occurs, the infusion is immediately stopped, antihistamines are administered (both histamine-1 and histamine-2 receptor blockers) and epinephrine is also administered in severe anaphylactic reactions.
Serum sickness is uncommon after antivenom treatment. When it occurs, it manifests with fever, rash, and arthralgias. Treatment is with PO prednisone, 1 mg/kg once daily, and the dose is tapered over 2 weeks.
The antivenom is administered intravenously (IV) and the dosage depends on envenomation severity and not on the body weight or age of the patient. The antivenom should be administered according to the instructions in the package insert.
Antivenom in some cases can cause an allergic reaction that may range from mild urticaria to severe anaphylaxis. With modern antivenoms, acute severe allergic reactions are relatively rare. If an acute allergic reaction occurs, the infusion is immediately stopped, antihistamines are administered (both histamine-1 and histamine-2 receptor blockers) and epinephrine is also administered in severe anaphylactic reactions.
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Bibliography
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