Snake Bites English

Snake Bites and Effects of Snake Venom

In Sweden, bites from venomous snakes are primarily caused by the common European adder (Vipera berus), the only venomous species that occurs naturally in the country. Snake bites usually happen along the coasts, especially during the summer. Approximately 70 patients are hospitalized in Sweden each year due to snake bites. Adult adders grow to around 60 cm in length and are gray or light brown with a characteristic black zigzag pattern on their backs, but they can also be completely black or gray. Younger specimens may also be reddish-brown. Adders can sometimes be mistaken for grass snakes, which have round pupils, unlike adders that have vertical slit-shaped pupils. Grass snakes are usually larger than adders and can grow over a meter in length. They typically have two yellow, white, or orange spots on the back of their heads.

Adder venom contains a variety of proteolytic enzymes (proteases, peptidases, hyaluronidase, phospholipases, phosphodiesterases, and L-amino acid oxidase) that primarily cause local symptoms such as swelling, pain, and bleeding, but can also lead to systemic symptoms like fainting, dizziness, nausea, vomiting, respiratory difficulties, and shock. The venom is hemorrhagic and necrotic but not neurotoxic. Adder venom can cause significant focal necrosis with blistering, particularly in fingers and toes, but reactions are usually limited to moderate redness, swelling, and characteristic bite marks. The adder’s fangs are approximately 4 mm long and leave a typical bite mark with two puncture marks (“fang marks”) about 6-9 mm apart. The venom can also lead to bleeding, thrombosis, and disseminated intravascular coagulation (DIC).

Snakes are typically classified into Viperidae (vipers) and Elapidae (elapid snakes). Among the Viperidae species are European vipers, including the Swedish adder, rattlesnakes, and Russell’s viper. Among the Elapidae species are cobras, mambas, coral snakes, taipans, and kraits (Southeast Asia). Most elapid species produce neurotoxic effects, while viperid species primarily cause muscle breakdown and coagulation disturbances, including disseminated intravascular coagulation (DIC). In Sweden, approximately 200 snake bites occur each year, with only a few fatalities each decade—the most recent known death occurred in 2000. Across Europe, the mortality rate from snake bites is reported to be 30-50 people per year. The mortality rate from adder bites is as low as 1-2 per thousand and continues to decrease.

A number of exotic snakes are kept in both private and public terrariums. Therefore, treating snake bites from tropical venomous snakes is not uncommon in Sweden. Regulations for owning venomous snakes privately vary across the country and are determined by the regional health authorities. It is estimated that there are at least 120 different species of venomous snakes in Sweden.

Many tropical venomous snakes can cause life-threatening symptoms requiring treatment with antivenom. About twenty specific antivenoms are available in Sweden, covering most snake species present in the country. Several antivenoms are polyvalent, meaning they work against more than one type of venom. On the other hand, snakes of the same species but different subspecies, such as rattlesnakes, may require treatment with different types of antivenom. Specific monovalent sera with fractionated antibodies are the most effective. Fractionated antibody sera cause significantly fewer allergic reactions compared to unfractionated sera (e.g., Zagreb serum). Therefore, it is important to identify the snake species to ensure the correct antivenom is used. Experts who can identify snakes are available at places like the Skansen Aquarium in Stockholm and Universeum in Gothenburg.

Antivenom for adder bites (Vipera Tab) is available at major hospitals around the country, though availability can vary significantly. It is important that each hospital maintains an up-to-date list of available antivenoms. Note the expiration dates. Apoteket Scheele in Stockholm has a central stock of antivenoms, which can be requested if needed. Antivenoms from Apoteket Scheele can reach any healthcare facility in Sweden within 4-6 hours when urgently requested.

The mortality rate from tropical snake bites varies by country and snake species. In Africa, Southeast Asia, and India, the mortality rate is significantly higher than in Europe, partly due to longer distances to medical care and poorer access to relevant antivenoms.

Significantly more deaths occur in Asia compared to Australia, where only 2-3 deaths per year are recorded.

Among the world’s most venomous snakes are the king cobra, black mamba, and the Australian (brown) taipan. The venom potency varies significantly between different variants within the same species, such as different cobra species. General symptoms are more pronounced when the bite site is more centrally located on the body, such as on the torso and around the head. Older individuals and young children are generally more sensitive, as are people with asthma and allergies. Local symptoms are more pronounced on the extremities. The most common bite sites are on the feet and hands. The risk of compartment syndrome increases with peripheral bites, such as on a hand or foot. Men are more likely to be bitten than women. In various studies, snake bites have been more than twice as common among men as among women. Snake bites are most common in people aged 20-50 years.

SYMPTOMS

Symptoms are generally either local or systemic. Systemic symptoms indicate severe envenomation. About 25% of adder bites cause systemic symptoms, while 75% cause only local symptoms, such as redness, swelling, and pain around the bite site. Bites from the Swedish adder resemble bites from many exotic venomous snakes, but most adder bites result only in local symptoms. In a Swedish study of 231 cases, severe bites accounted for 13% of all cases, and 29% had moderate symptoms (Karlsson-Stiber, 2006).

Common symptoms of snake bites include pain followed by swelling and discoloration. The pain is often intense and requires analgesics. Some tropical snakes, such as the many-banded krait, which injects neurotoxic venom, can cause severe paralysis, including respiratory paralysis, without significant local symptoms or pain.

Snake venom is primarily hemorrhagic, necrotic, or neurotoxic, depending on the species. The dominant symptoms often include local swelling, pain, discoloration, and in severe cases, tissue necrosis. Hemorrhagic toxins cause more extensive tissue damage with swelling, bleeding, and necrosis compared to neurotoxins. The risk of compartment syndrome is significant with snake bites in the arms and legs. Neurotoxic venom (cobra, many-banded krait) can result in complete paralysis with respiratory failure, requiring assisted ventilation and intensive care.

Snake venom primarily spreads through tissue via the lymphatic system. Hemorrhagic snake venom affects the blood’s ability to clot and can induce increased bleeding tendencies and disseminated intravascular coagulation (DIC) (especially with Russell’s viper). Some venoms can cause bleeding disorders with thrombocytopenia without DIC. It is important to monitor the patient’s bleeding status clinically and through laboratory parameters. In cases of bites from highly venomous tropical snakes, both the initial clinical presentation and initial coagulation tests may be completely normal, only to become severely deranged within 24 hours with marked thrombocytopenia and increased bleeding tendencies. Bleeding should be monitored in the oral mucosa, eyes, and retroperitoneum, where large spontaneous hemorrhages can occur (CT should be considered if there are clinical signs of bleeding).

Swelling following a snake bite can vary significantly and may progress over several days. Swelling that spreads over a major joint, such as the elbow after a hand bite or the knee after a foot bite, indicates a severe bite and is an indication for antivenom treatment. The swelling itself can cause compartment syndrome in areas like the hand or leg. Compartment syndrome may require surgical intervention, such as fasciotomy (preferably avoided), but the bite site should primarily be left alone and not incised or cauterized. However, tissue pressure should be measured in cases of compartment syndrome.

Discoloration is often hemorrhagic, red-blue, or dark purple, turning black as tissue necrosis sets in. Necrosis affects the skin, soft tissues, and deeper structures. Fingers may need partial or complete amputation. Discoloration and swelling can be extensive even without necrosis, sometimes affecting an entire leg and extending up to the torso.

The bite site usually shows, but does not always display, two fang marks spaced 0.5 to 2 cm apart. The distance between the fangs can provide clues about the snake species and its size. There may be one, two, or three punctate or streak-like bite marks (“fang marks”).

Local Symptoms

• Pain
• Swelling
• Discoloration (hemorrhages, ecchymoses)
• Numbness
• Paralysis
• Paresthesias
• Necrosis
• Bleeding
• Compartment syndrome

Systemic Symptoms

• Nausea
• Vomiting
• Anxiety, panic
• Restlessness, hyperventilation
• Pain
• Fainting
• Heart palpitations, tachycardia
• Hypotension (low blood pressure)
• Circulatory shock
• Shortness of breath, bronchoconstriction, obstruction
• Allergic reaction
• Coagulation disturbances, general DIC

Initial Management and Measures

When a patient presents with a venomous snake bite, it should be managed promptly.

In the case of severe injury, immediately notify the following individuals:

• The responsible on-call physician at the emergency department
• The relevant on-call consultant at the emergency department
• Anesthesiologist or intensive care consultant

When possible, also contact the following:

• The Poison Information Center in Stockholm, phone: 08-331 231
• Pharmacist responsible for the hospital’s antidote stock
• Police or fire department to capture a loose snake
• Snake expert to identify the snake, if unknown

Patient Management

• Ensure that all snake bite patients come to the hospital and do not wait at home, even in mild cases.
• The patient should be treated immediately and not left to wait without supervision. Even in relatively unaffected individuals, serious symptoms can develop suddenly.
• The responsible physician, in consultation with the ICU on-call doctor, decides whether to admit the patient to intensive care. If antivenom treatment is required, admission to the ICU is recommended.
• Antivenom can be urgently requested from Apoteket Scheele in Stockholm (phone: 0771-450450) for emergency air or taxi transport. Scheele can usually deliver within 3 hours. The Skansen Aquarium in Stockholm (phone: 08-442 80 39) and a few other private terrariums supply antivenoms effective against exotic snake bites. Antivenom is generally polyvalent, meaning it is effective against more than one type of venom. Check expiration dates. Some antivenoms are considered effective for a certain time after the expiration date.

Treatment of Snake Bites

General Advice

• Create a calm environment for the patient. The patient should sit or lie down, even during transport. Try to prevent the patient from panicking. Administer sedatives or analgesics as needed, for example, injection diazepam (Stesolid) (5-10 mg IV) for anxiety and distress, or morphine/ketobemidone (Morphine/Ketogan) (5-10 mg IV) for pain and distress. The patient should not run on the way to the hospital.
• Compression bandage if necessary. In some countries, such as Australia, a firm elastic bandage is routinely applied to the bitten limb to slow the absorption of venom and reduce edema. The bandage is applied distally and wrapped proximally. It prevents the spread of venom and reduces edema formation. The bandage should not be too tight. The bandage is usually not removed until the patient has received antivenom. The idea is that antibodies should be present in the blood when the antigen (snake venom) enters the systemic circulation. Compression bandages work better after bites from neurotoxic snakes than from necrotizing hemorrhagic venoms. Therefore, it is generally more applicable after bites from Australian or Asian snakes than from European, African, or American species. Better suited for elapids than vipers.
• Immobilize the bitten limb, keeping it elevated after bandaging. For hand bites, the hand can be placed on a pillow or suspended in a sling.
• Leave the bite site alone.
• Administer specific antivenom in cases of severe envenomation. Treatment should begin within 12 hours of the bite, preferably within 4 hours. In cases of severe systemic symptoms, antivenom treatment should start as soon as possible. Shock can develop within 30 minutes of a snake bite but is more common after 2-3 hours.
• Tetanus prophylaxis is recommended, but the scientific evidence is weak.
• Antibiotic treatment should only be given if there are signs of infection. Routine antibiotic treatment is not needed.
• The bitten person’s dismissive comments like “it’s not that bad,” “I feel fine” are common and should be ignored!

Avoid the following

• Epidural anesthesia. In cases of leg pain, epidural anesthesia should be avoided due to the increased risk of thrombosis/bleeding complications.
• Having the patient drive themselves to the hospital
• Do not suck, cut, cool, heat, or cauterize the bite site.
• Avoid the patient running or exerting themselves on the way to the hospital
• Avoid constricting bandages; do not wrap from above downwards.
• Hysteria and panic
• Treatment with uncertain or expired antivenom for a bite from an unidentified snake.
• Antivenom treatment when only moderate local symptoms are present.

Mild Bites

When only local redness and swelling are present.

The patient is managed in the emergency department or a medical acute care ward (MAVA) or equivalent. Patients in high-risk groups, such as the elderly, frail, young children, and asthmatics, should be observed for at least 8 hours before being discharged home.

• The patient is managed by the on-call physician.
• Insert at least one IV line. Take Hb, WBC, platelets, and urinalysis. If needed, administer IV fluids, such as Ringer’s acetate.
• Admit all children and systemically affected patients to the hospital for at least one day.
• Unaffected patients should be observed for at least 6-8 hours.
• Corticosteroids (Solu-Cortef, 100 mg IV or IM). The scientific evidence for steroid treatment in adder bites is weak, but it is a well-established routine and is recommended primarily for allergic symptoms, bronchospasm, or after treatment with serum derived from horses. Steroids are also likely helpful in significant inflammatory reactions.
• Antihistamines, such as clemastine (Tavegyl, 1 mg IV). Note that treatment can be sedating. Scientific evidence of efficacy is weak.
• Morphine/ketobemidone (Morphine/Ketogan) (5-10 mg IV) for pain.
• Monitor and follow blood tests, watching for the following:
  – Metabolic acidosis (arterial blood gas)
  – Hemolysis (S-haptoglobin, LD), leukocytosis, thrombocytopenia
  – Rhabdomyolysis (serum myoglobin, CK)
  – Hb, WBC, platelets, CRP, PT/INR

Severe Bites

There is a strong local reaction or clear systemic effects (clouded consciousness, low blood pressure (systolic blood pressure < 90 mmHg), high heart rate, high respiratory rate).

Patients with pre-shock/shock should be managed in an intensive care unit (ICU). Monitor coagulation parameters closely upon arrival and after 12 and 24 hours.

• Corticosteroids (Solu-Cortef, 100-200 mg IV).
• Administer antihistamines (Tavegyl, 1 mg IV x 2). Note that the treatment can be sedating. Scientific evidence of efficacy is weak.
• Administer antivenom, following instructions below.
• Immobilize the bitten limb, preferably elevated. In the case of hand bites, suspend the arm in a sling attached to a bedpost or similar.
• Morphine/ketobemidone (5-10 mg IV) for pain. Note that the treatment itself can be sedating.
• In cases of allergic/anaphylactic reactions or bronchospasm, administer adrenaline (1 mg/mL, 0.3-0.5 mL IM into the lateral thigh).
• In cases of bronchospasm, administer beta-agonist inhalation therapy, such as salbutamol or terbutaline (Ventoline/Bricanyl).
• In cases of circulatory shock, adrenaline can be administered intravenously, 0.1-0.5 mg (0.1 mg/mL) IV titrated according to blood pressure.
• Provide adequate fluid replacement, such as Ringer’s acetate, Voluven, or Macrodex. Provide volume replacement with balanced electrolyte solutions and colloids, preferably dextran. However, large amounts of dextran should not be given, as it can affect blood clotting.
• If dextran is not given, consider other thromboprophylaxis, such as dalteparin sodium (Fragmin) in low doses (2,500-5,000 units SC), or enoxaparin sodium (Clexane), 40 mg SC regardless of weight.
• Inotropic support and other shock treatments are provided according to standard indications for circulatory failure, such as noradrenaline infusion.
• Administer oxygen via nasal cannula or nasal catheter.
• Monitor Hb, WBC, platelets, CRP, myoglobin, PT/INR, APTT, FDP, S-haptoglobin, and LD.
• Consider thromboelastogram or ACT.

Antivenom Treatment

Treatment should begin within 12 hours of the snake bite, preferably within 4 hours. In cases of severe systemic symptoms, antivenom treatment should start as soon as possible. Antivenom treatment is the most effective treatment for severe snake bites.

Antivenom treatment should be administered when severe systemic symptoms are present or when there is marked progression of swelling and discoloration, such as over a major joint (knee, elbow).

Indications for starting antivenom treatment include:

• Circulatory compromise that does not respond to initial fluid resuscitation
• Unconsciousness or reduced consciousness
• Prolonged or recurrent gastrointestinal symptoms
• Bronchospasm or stridor
• Progression of the local reaction in the bitten limb, with swelling spreading over a joint, such as the knee or elbow within 6 hours.
• Clear systemic involvement

If there is doubt, the following factors support the indication for antivenom treatment:

• Leukocytosis > 15-20 x 10⁹
• Metabolic acidosis
• Bites from highly venomous snakes, such as certain cobras, black mambas, or Australian taipans.
• Hemolysis (elevated LD, low haptoglobin)
• New-onset ECG changes:
  – Arrhythmias
  – ST-T changes
  – Other signs of ischemia
• Coagulation disorders (thrombocytopenia, elevated PT/INR or APTT)

Adder bites are usually treated with the antidote Vipera Tab. Two ampoules = 200 mg are dissolved in 10 mL sterile water and diluted in 100 mL NaCl (9 mg/mL) and administered as an intravenous infusion over 30 minutes. The same dose is given to children as to adults. A second dose (200 mg) may be indicated in cases of recurrent circulatory compromise, persistent gastrointestinal symptoms, severe coagulopathy, hemolysis, or continued rapid progression of the local reaction, with a risk of involvement of the trunk.

When administering antivenom after bites from tropical snakes, follow the instructions on the package insert carefully.

If in doubt, consult the Poison Information Center in Stockholm.

Follow-up After Snake Bite

One to two weeks after antivenom treatment, an allergic reaction, known as serum sickness, can occur. Instruct the patient to report any symptoms such as fever, joint pain, or fatigue. Serum sickness should be treated with corticosteroids.

After severe bites or when antivenom has been administered for tropical snakes, a follow-up outpatient visit is recommended 1-2 weeks after discharge. At that time, check ESR, CRP, Hb, platelets, creatinine, and WBC. Severe fatigue and general malaise can persist for a long time after a snake bite, as can residual local symptoms such as swelling and numbness with paresthesias. Follow-up visits should be planned.

ICD-10

Toxic effect of snake venom T63.0

References

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