Snakebites

Overview

Epidemiology

• Approximately 15% of snake species worldwide are dangerous.
• Worldwide: > 100,000 deaths yearly
• In the United States:
  • Approximately 7,000–8,000 venomous snakebites annually
  • < 10 deaths per year 
  • Rattlesnakes cause the most fatalities.

Clinically relevant species

Some important venomous snakes in the United States include:

• Viperidae family, Crotalinae subfamily (“pit vipers” account for 95% of cases in the United States):
  • Rattlesnakes
  • Copperheads
  • Cottonmouths (also known as water moccasins)
• Elapidae family: coral snakes

Pathophysiology

• Not all snake bites result in envenomation.  
• Snake venom components:
  • Local toxins:
    • Proteases Proteases Proteins and Peptides
    • Collagenase
    • Phospholipases
    • 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
  • Systemic toxins:
    • Proteins Proteins Linear polypeptides that are synthesized on ribosomes and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of amino acids determines the shape the polypeptide will take, during protein folding, and the function of the protein. Energy Homeostasis that interfere with blood clotting
    • Neurotoxins
    • Myotoxins
    • Some toxins produce renal toxicity Toxicity Dosage Calculation and cardiotoxicity directly or through the other systemic effects (e.g., 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).
• Envenomation effects:
  • Local and systemic allergic response
  • ↑ Capillary permeability → extravasation of plasma Plasma The residual portion of blood that is left after removal of blood cells by centrifugation without prior blood coagulation. Transfusion Products
  • Hemolysis and coagulopathy
  • Tissue necrosis Necrosis The death of cells in an organ or tissue due to disease, injury or failure of the blood supply. Ischemic Cell Damage
  • Acetylcholine Acetylcholine A neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system. Receptors and Neurotransmitters of the CNS receptor Receptor Receptors are proteins located either on the surface of or within a cell that can bind to signaling molecules known as ligands (e.g., hormones) and cause some type of response within the cell. Receptors antagonism at neuromuscular junctions (coral snake) → paralysis

Clinical Presentation

General presentation

• Bite marks may not be visible.
• Site findings of bites:
  • Fang marks 
  • Scratches
• Clinical signs depend on:
  • Age and size of the victim (children may have more serious presentations)
  • Species of snake
    • Crotalid envenomation: local damage and possible systemic effects (e.g., hematologic)
    • Coral snake envenomation: motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology and sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology abnormalities, rarely local injury or necrosis Necrosis The death of cells in an organ or tissue due to disease, injury or failure of the blood supply. Ischemic Cell Damage
  • Number and location of bites
  • Quantity and toxicity Toxicity Dosage Calculation of the venom

Local signs of envenomation

• Edema Edema Edema is a condition in which excess serous fluid accumulates in the body cavity or interstitial space of connective tissues. Edema is a symptom observed in several medical conditions. It can be categorized into 2 types, namely, peripheral (in the extremities) and internal (in an organ or body cavity). Edema and erythema Erythema Redness of the skin produced by congestion of the capillaries. This condition may result from a variety of disease processes. Chalazion 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
• Ecchymosis Ecchymosis Extravasation of blood into the skin, resulting in a nonelevated, rounded or irregular, blue or purplish patch, larger than a petechia. Orbital Fractures
• Bullae Bullae Erythema Multiforme development
• Necrosis Necrosis The death of cells in an organ or tissue due to disease, injury or failure of the blood supply. Ischemic Cell Damage

Systemic signs and symptoms of envenomation

• Nausea Nausea An unpleasant sensation in the stomach usually accompanied by the urge to vomit. Common causes are early pregnancy, sea and motion sickness, emotional stress, intense pain, food poisoning, and various enteroviruses. Antiemetics and vomiting Vomiting The forcible expulsion of the contents of the stomach through the mouth. Hypokalemia
• 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
• Diaphoresis
• Anxiety Anxiety Feelings or emotions of dread, apprehension, and impending disaster but not disabling as with anxiety disorders. Generalized Anxiety Disorder
• Paresthesias Paresthesias Subjective cutaneous sensations (e.g., cold, warmth, tingling, pressure, etc.) that are experienced spontaneously in the absence of stimulation. Posterior Cord Syndrome
• Altered sensorium
• Cranial nerve palsies Cranial Nerve Palsies Cranial nerve palsy is a congenital or acquired dysfunction of 1 or more cranial nerves that will, in turn, lead to focal neurologic abnormalities in movement or autonomic dysfunction of its territory. Head/neck trauma, mass effect, infectious processes, and ischemia/infarction are among the many etiologies for these dysfunctions. Diagnosis is initially clinical and supported by diagnostic aids. Management includes both symptomatic measures and interventions aimed at correcting the underlying cause. Cranial Nerve Palsies
• Flaccid muscles (including respiratory muscle paralysis)

Complications

• 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 Airway ABCDE Assessment swelling Swelling Inflammation
• Respiratory failure Respiratory failure Respiratory failure is a syndrome that develops when the respiratory system is unable to maintain oxygenation and/or ventilation. Respiratory failure may be acute or chronic and is classified as hypoxemic, hypercapnic, or a combination of the two. Respiratory Failure
• Renal failure Renal failure Conditions in which the kidneys perform below the normal level in the ability to remove wastes, concentrate urine, and maintain electrolyte balance; blood pressure; and calcium metabolism. Renal insufficiency can be classified by the degree of kidney damage (as measured by the level of proteinuria) and reduction in glomerular filtration rate. Crush Syndrome

Diagnosis and Management

Diagnosis

The diagnosis of a snake bite is clinical and aided by the identification Identification Defense Mechanisms of the snake. Photos of the snake (if able to be taken safely) help expedite the diagnosis and management.

Management

• 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
    • Complete blood count
    • Renal and hepatic function
    • Creatine Creatine An amino acid that occurs in vertebrate tissues and in urine. In muscle tissue, creatine generally occurs as phosphocreatine. Creatine is excreted as creatinine in the urine. Acute Kidney Injury kinase and urine myoglobin Myoglobin A conjugated protein which is the oxygen-transporting pigment of muscle. It is made up of one globin polypeptide chain and one heme group. Rhabdomyolysis (for rhabdomyolysis Rhabdomyolysis Rhabdomyolysis is characterized by muscle necrosis and the release of toxic intracellular contents, especially myoglobin, into the circulation. Rhabdomyolysis)
• Dry bites (no envenomation):
  • Observation
  • Recheck labs before discharge
• 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 Analgesia Methods of pain relief that may be used with or in place of analgesics. Anesthesiology: History and Basic Concepts ( NSAIDs NSAIDS Primary vs Secondary Headaches may worsen coagulopathy)
  • Vasopressors Vasopressors Sepsis in Children 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
  • Blood products as needed for hemorrhagic effects
  • Administration of the following should be under the guidance of a toxicologist or poison control:
    • Antivenom in case of life-threatening systemic effects and/or worsening local damage
    • Neostigmine Neostigmine A cholinesterase inhibitor used in the treatment of myasthenia gravis and to reverse the effects of muscle relaxants such as gallamine and tubocurarine. Neostigmine, unlike physostigmine, does not cross the blood-brain barrier. Cholinomimetic Drugs trial (given with atropine Atropine An alkaloid, originally from atropa belladonna, but found in other plants, mainly solanaceae. Hyoscyamine is the 3(s)-endo isomer of atropine. Anticholinergic Drugs) in case of paralysis
• The use of tourniquets, icing the wound, and “cutting and sucking” are not helpful and should be discouraged.

Differential Diagnosis

• Dog and cat bites Cat bites Dog and cat bites can cause superficial and deep tissue destruction, as well as serious wound infections. 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 Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease. 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. Bones: Structure and Types, may occur. The diagnosis is clinical, and cultures should be obtained if the wound appears infected. Management requires fastidious Fastidious Bordetella wound care and antibiotics for high-risk or infected wounds. 
• Spider Spider Arthropods of the class arachnida, order araneae. Except for mites and ticks, spiders constitute the largest order of arachnids, with approximately 37, 000 species having been described. The majority of spiders are harmless, although some species can be regarded as moderately harmful since their bites can lead to quite severe local symptoms. Spider Bites bites: the brown recluse spider Spider Arthropods of the class arachnida, order araneae. Except for mites and ticks, spiders constitute the largest order of arachnids, with approximately 37, 000 species having been described. The majority of spiders are harmless, although some species can be regarded as moderately harmful since their bites can lead to quite severe local symptoms. Spider Bites contains a necrotizing venom Necrotizing Venom Spider Bites that can lead to a painful, blistering, necrotic wound; fevers; myalgias Myalgias Painful sensation in the muscles. Tick-borne Encephalitis Virus; 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 Renal failure Conditions in which the kidneys perform below the normal level in the ability to remove wastes, concentrate urine, and maintain electrolyte balance; blood pressure; and calcium metabolism. Renal insufficiency can be classified by the degree of kidney damage (as measured by the level of proteinuria) and reduction in glomerular filtration rate. Crush Syndrome. A black widow spider Spider Arthropods of the class arachnida, order araneae. Except for mites and ticks, spiders constitute the largest order of arachnids, with approximately 37, 000 species having been described. The majority of spiders are harmless, although some species can be regarded as moderately harmful since their bites can lead to quite severe local symptoms. Spider Bites’s neurotoxic venom Neurotoxic Venom Spider Bites can cause muscle cramping and rigidity Rigidity Continuous involuntary sustained muscle contraction which is often a manifestation of basal ganglia diseases. When an affected muscle is passively stretched, the degree of resistance remains constant regardless of the rate at which the muscle is stretched. This feature helps to distinguish rigidity from muscle spasticity. Megacolon, vital sign instability, lacrimation, salivation, ptosis Ptosis Cranial Nerve Palsies, and respiratory distress. The diagnosis is clinical. Management includes wound care, pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways management, antivenom for black widow bites, and delayed debridement Debridement The removal of foreign material and devitalized or contaminated tissue from or adjacent to a traumatic or infected lesion until surrounding healthy tissue is exposed. Stevens-Johnson Syndrome of necrotic tissue in brown recluse bites.
• Insect sting: bee, wasp, and ant stings can cause envenomation with localized swelling Swelling Inflammation. Some patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship will develop a severe allergic reaction, including anaphylaxis Anaphylaxis An acute hypersensitivity reaction due to exposure to a previously encountered antigen. The reaction may include rapidly progressing urticaria, respiratory distress, vascular collapse, systemic shock, and death. Type I Hypersensitivity Reaction. Neurologic manifestations, coagulopathy, and tissue necrosis Necrosis The death of cells in an organ or tissue due to disease, injury or failure of the blood supply. Ischemic Cell Damage 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 An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways control, and emergency care for anaphylaxis Anaphylaxis An acute hypersensitivity reaction due to exposure to a previously encountered antigen. The reaction may include rapidly progressing urticaria, respiratory distress, vascular collapse, systemic shock, and death. Type I Hypersensitivity Reaction.
• 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 Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship will have pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways and swelling Swelling Inflammation at the site of the sting. Systemic manifestations can include muscle spasms Spasms An involuntary contraction of a muscle or group of muscles. Spasms may involve skeletal muscle or smooth muscle. Ion Channel Myopathy, diaphoresis, abnormal neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess and head movements, tachycardia Tachycardia Abnormally rapid heartbeat, usually with a heart rate above 100 beats per minute for adults. Tachycardia accompanied by disturbance in the cardiac depolarization (cardiac arrhythmia) is called tachyarrhythmia. Sepsis in Children, 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 An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways 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 Spasms An involuntary contraction of a muscle or group of muscles. Spasms may involve skeletal muscle or smooth muscle. Ion Channel Myopathy, and antivenom.
• Deep venous thrombosis Venous thrombosis The formation or presence of a blood clot (thrombus) within a vein. Budd-Chiari Syndrome: 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: Histology of an extremity. This clotting may be asymptomatic or present with limb swelling Swelling Inflammation, erythema Erythema Redness of the skin produced by congestion of the capillaries. This condition may result from a variety of disease processes. Chalazion, and pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways. A bite site and systemic symptoms are not present. The diagnosis is confirmed with vascular ultrasound. Unless there are contraindications Contraindications A condition or factor associated with a recipient that makes the use of a drug, procedure, or physical agent improper or inadvisable. Contraindications may be absolute (life threatening) or relative (higher risk of complications in which benefits may outweigh risks). Noninvasive Ventilation, this condition is managed with anticoagulation Anticoagulation Pulmonary Hypertension Drugs.