Achieving Control

3 Areas of Pathological Impact

A single venom contains a wide array of toxins—necrotoxins, pre- and postsynaptic neurotoxins, and nephrotoxins, among others. This complexity, along with other biological factors, makes it difficult in clinical practice to predict specific effects of an individual envenomation.1,2*

However, all envenomations can exhibit some or all of the following effects1,2:
Local, systemic, and hematologic effects of pit viper envenomation

*Approximately 1 in every 4 bites is "dry," meaning no venom has been injected.
Local Effects1,2
Pain and local soft tissue damage are the first symptoms of envenomation. Necrotoxins may produce clinical effects almost immediately postbite, resulting in tissue digestion and vascular permeability.
Edema
  • Is produced by permeable vessels, caused by venom, allowing fluid and blood to extravasate
  • Is the first objective sign of envenomation and should prompt immediate attention
  • Can progress to hypovolemic shock
  • Decreases slowly with treatment and is therefore a poor indicator of clinical improvement
  • Creates skin issues relative to the extent of the edema
    • Loss of skin elasticity
    • Skin stretches and fissures
    • Fissures, while generally superficial, should be monitored as sources of secondary infection
Ecchymosis
  • May occur with edema
  • May indicate severity of envenomation by speed of progression
  • Caused by bleeding into skin due to venom-induced coagulopathy
Vesiculations and Bullae
  • May be filled with clear serous fluid (vesicles) or with blood (bullae)
  • Develops most frequently in the bite area, but may be visible over the entire extremity
Skin Necrosis
  • Can result from tissue destruction by venom proteins (snake venom metalloproteinases)
  • May occur distal to bite site
Potential Consequences
  • Partial or complete loss of affected limbs
  • Loss of joint functionality
  • Loss or impairment of tactile sensation
  • Infection
  • Cosmetic issues
Systemic Effects1,2
General systemic effects include:
  • Headache
  • Diarrhea
  • Nausea
  • Syncope
  • Vomiting
  • Convulsions
  • Abdominal Pain
  • Metallic taste (likely due to metalloproteinases in the venom)
Specific systemic effects include, but not limited to:
Neurotoxic Paralysis
  • Caused by pre- and/or postsynaptic neurotoxins
    • Presynaptic paralysis usually involves terminal axon damage. Reversal requires regeneration of axons, which takes days, weeks, or even months
  • May take 1 to 12 hours to become evident
  • Is progressive, often first seen in cranial nerves
    • Is easily missed if not specifically sought in exam
  • Is also evidenced early by ptosis, ophthalmoplegia, dysarthria, and/or dysphagia
  • Can lead to respiratory failure
    • Paralysis of the diaphragm may be delayed up to 24 hours post-bite
Cardiac Effects
  • Hypo- or hypertension
  • Bradycardia
  • Tachycardia
Potential Consequences
  • Death is a possibility
  • Irreversible damage
  • Respiratory compromise/failure
  • Neurologic deficits
  • Cardiovascular/pulmonary collapse due to shock
  • End organ damage
Hematologic Effects1-3
The 3 hematologic effects of envenomation are
Coagulopathy
  • Decreased fibrinogen levels
  • Elevated International Normalized Ratio (INR) and Prothrombin Time (PT)
Thrombocytopenia
  • Defined as less than 150,000 platelets/microliter (platelets <50,000 are considered clinically important4)
  • In severe pit viper envenomations, platelet counts may be undetectable
  • Transfusion alone can produce transient improvement in coagulation parameters and platelet counts, but rarely has a sustained effect in the absence of adequate dosing of antivenom
Bleeding
  • Oozing of blood from the bite site and ecchymosis of the surrounding tissue
  • Nuisance bleeding, such as gingival bleeding or haemolacria, or more serious bleeding, such as significant epistaxis, gastrointestinal bleeding, intracranial hemorrhage
  • Medically significant and spontaneous bleeding is rare
Potential Consequences
  • Coagulation abnormalities
  • Increased risk of bleeding complications
  • Significant ecchymosis
  • Anemia

Don’t let myths about envenomation treatment hinder judgment when time is crucial.

References:

1. Smith J, Bush S. Envenomations by reptiles in the United States. In: Mackessy SP, ed. Handbook of Venoms and Toxins of Reptiles. Boca Raton, FL: CRC Press; 2010:475-488. 2. Lavonas EJ, Ruha AM, Banner W, et al. Unified treatment algorithm for the management of crotaline snakebite in the United States: results of an evidence-informed consensus workshop. BMC Emerg Med. 2011;11:2. 3. Lavonas EJ, Khatri V, Daugherty C, Bucher-Bartelson B, King T, Dart RC. Medically significant late bleeding after treated crotaline envenomation: a systematic review. Ann Emerg Med. 2014;63(1):71-78. 4. Yip L. Rational use of crotalidae polyvalent immune Fab (ovine) in the management of crotaline bite.[comment] Ann Emerg Med. 2002;39:648–650.