- Approximately 15% of snake species worldwide are dangerous.
- Worldwide: > 100,000 deaths yearly
- In the United States:
- Approximately 45,000 snakebites per year
- 7,000–8,000 of these bites are venomous.
- < 10 deaths per year
- Rattlesnakes cause the most fatalities.
Clinically relevant species
Some important venomous snakes in the United States include:
- Crotalidae family (accounts for 95% of cases in the United States):
- Cottonmouths (also known as water moccasins)
- Elapidae family: coral snakes
- Not all snake bites result in envenomation.
- Snake venom often contains:
- Other enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body's constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes
- Envenomation effects:
- Local and systemic allergic response
- ↑ Capillary permeability → extravasation of plasma
- Hemolysis and coagulopathy
- Tissue necrosis
- Acetylcholine receptor antagonism at neuromuscular junctions (coral snake)
- Bite marks may not be visible.
- Clinical signs depend on:
- Age and size of the victim
- Species of snake
- Number and location of bites
- Quantity and toxicity of the venom
- Bite-site findings:
- Fang marks
Local signs of envenomation
- Edema and erythema of bite site and surrounding tissue
- Oozing from the wound
- Tender regional lymphadenopathy Lymphadenopathy Lymphadenopathy is lymph node enlargement (> 1 cm) and is benign and self-limited in most patients. Etiologies include malignancy, infection, and autoimmune disorders, as well as iatrogenic causes such as the use of certain medications. Generalized lymphadenopathy often indicates underlying systemic disease. Lymphadenopathy
- Warmth over the bite area
- Bullae development
Systemic signs of envenomation
- Nausea and vomiting
- Diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea
- Altered sensorium
- Cranial nerve palsies
- Flaccid muscles (including respiratory muscle paralysis)
- Hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension and shock Shock Shock is a life-threatening condition associated with impaired circulation that results in tissue hypoxia. The different types of shock are based on the underlying cause: distributive (↑ cardiac output (CO), ↓ systemic vascular resistance (SVR)), cardiogenic (↓ CO, ↑ SVR), hypovolemic (↓ CO, ↑ SVR), obstructive (↓ CO), and mixed. Types of Shock
- Thrombocytopenia Thrombocytopenia Thrombocytopenia occurs when the platelet count is < 150,000 per microliter. The normal range for platelets is usually 150,000-450,000/µL of whole blood. Thrombocytopenia can be a result of decreased production, increased destruction, or splenic sequestration of platelets. Patients are often asymptomatic until platelet counts are < 50,000/µL. Thrombocytopenia
- Coagulopathy and spontaneous bleeding
- Compartment syndrome Compartment Syndrome Compartment syndrome is a surgical emergency usually occurring secondary to trauma. The condition is marked by increased pressure within a compartment that compromises the circulation and function of the tissues within that space. Compartment Syndrome
- Airway swelling
- Respiratory failure
- Renal failure
Diagnosis and Management
The diagnosis of a snake bite is clinical and aided by the identification of the snake.
- General measures:
- Immobilize the affected extremity.
- Wound cleansing and care
- Ensure that tetanus Tetanus Tetanus is a bacterial infection caused by Clostridium tetani, a gram-positive obligate anaerobic bacterium commonly found in soil that enters the body through a contaminated wound. C. tetani produces a neurotoxin that blocks the release of inhibitory neurotransmitters and causes prolonged tonic muscle contractions. Tetanus immunizations are up to date.
- Hospital monitoring for signs of envenomation
- A poison control center should be consulted.
- Monitor laboratory studies:
- Coagulation panel
- Hemoglobin and platelets Platelets Platelets are small cell fragments involved in hemostasis. Thrombopoiesis takes place primarily in the bone marrow through a series of cell differentiation and is influenced by several cytokines. Platelets are formed after fragmentation of the megakaryocyte cytoplasm. Platelets
- Renal function
- Medical therapy:
- Intravenous fluid hydration
- Opioids Opioids Opiates are drugs that are derived from the sap of the opium poppy. Opiates have been used since antiquity for the relief of acute severe pain. Opioids are synthetic opiates with properties that are substantially similar to those of opiates. Opioid Analgesics for analgesia (NSAIDs may worsen coagulopathy)
- Vasopressors for shock Shock Shock is a life-threatening condition associated with impaired circulation that results in tissue hypoxia. The different types of shock are based on the underlying cause: distributive (↑ cardiac output (CO), ↓ systemic vascular resistance (SVR)), cardiogenic (↓ CO, ↑ SVR), hypovolemic (↓ CO, ↑ SVR), obstructive (↓ CO), and mixed. Types of Shock
- The use of tourniquets, icing the wound, and “cutting and sucking” are not helpful and should be discouraged.
- Dog and cat bites Dog and Cat bites Dog and cat bites can cause superficial and deep tissue destruction, as well as serious wound infections. Dog bites occur more frequently in men and children and often cause crushing or tearing trauma. Cat bites are more frequent in adult women and result in puncture wounds. Dog and Cat Bites: can cause superficial and deep tissue destruction as well as serious wound infections. The wound type depends on the animal but can include tearing, crush, or puncture wounds. Damage to deeper tissues, such as vessels, tendons, and bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Structure of Bones, may occur. The diagnosis is clinical, and cultures should be obtained if the wound appears infected. Management requires fastidious wound care and antibiotics for high-risk or infected wounds.
- Spider bites Spider bites Spider bites are a rare cause of morbidity and mortality. Almost all spiders are venomous, but the majority do not have the ability to penetrate skin for envenomation. Brown recluse and black widow spiders are the most common causes of serious systemic reactions in the United States. Spider Bites: the brown recluse spider contains a necrotizing venom that can lead to a painful, blistering, necrotic wound; fevers; myalgias; hemolysis; seizures Seizures A seizure is abnormal electrical activity of the neurons in the cerebral cortex that can manifest in numerous ways depending on the region of the brain affected. Seizures consist of a sudden imbalance that occurs between the excitatory and inhibitory signals in cortical neurons, creating a net excitation. The 2 major classes of seizures are focal and generalized. Seizures; and renal failure. A black widow spider’s neurotoxic venom can cause muscle cramping and rigidity, vital sign instability, lacrimation, salivation, ptosis, and respiratory distress. The diagnosis is clinical. Management includes wound care, pain management Pain Management Pain is defined as an unpleasant sensory and emotional experience associated with actual or potential tissue damage. Pain is a subjective experience. Acute pain lasts < 3 months and typically has a specific, identifiable cause. Pain Management, antivenom for black widow bites, and delayed debridement of necrotic tissue in brown recluse bites.
- Insect sting: bee, wasp, and ant stings can cause envenomation with localized swelling. Some patients will develop a severe allergic reaction, including anaphylaxis. Neurologic manifestations, coagulopathy, and tissue necrosis are not usually present. The diagnosis is clinical. Management includes removing the stinger (if present), antihistamines Antihistamines Antihistamines are drugs that target histamine receptors, particularly H1 and H2 receptors. H1 antagonists are competitive and reversible inhibitors of H1 receptors. First-generation antihistamines cross the blood-brain barrier and can cause sedation. Antihistamines, pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain control, and emergency care for anaphylaxis.
- Scorpion sting: most scorpion stings Scorpion stings Insect and scorpion stings are a rare cause of mortality. Hymenoptera insects and Centruroides scorpions can potentially lead to serious symptoms due to envenomation. Pain, swelling, erythema, and warmth are common at the site of a sting. Insect and Scorpion Stings are harmless. However, the bark scorpion is venomous. Patients will have pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain and swelling at the site of the sting. Systemic manifestations can include muscle spasms, diaphoresis, abnormal neck and head movements, tachycardia, hypertension Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension, and respiratory distress. The diagnosis is clinical. Management includes supportive care, pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain control, benzodiazepines Benzodiazepines Benzodiazepines work on the gamma-aminobutyric acid type A (GABAA) receptor to produce inhibitory effects on the CNS. Benzodiazepines do not mimic GABA, the main inhibitory neurotransmitter in humans, but instead potentiate GABA activity. Benzodiazepines for muscle spasms, and antivenom.
- Deep venous thrombosis: blood clotting in the deep veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins of an extremity. This clotting may be asymptomatic or present with limb swelling, erythema, and pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain. A bite site and systemic symptoms are not present. The diagnosis is confirmed with vascular ultrasound. Unless there are contraindications, this condition is managed with anticoagulation.
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