Approach
The diagnosis is based on patient history. The patient may report having been bitten by a snake or, if walking through tall grass or brush, the patient may have felt a bite without seeing the snake. The patient may be able to describe the snake or, in some cases, they may bring the snake with them.
On physical exam, fang marks are frequently, although not always, present.
Signs and symptom onset
Suspected Crotalinae envenomation
Complaints of pain, redness, or swelling at the bite site, along with nausea/vomiting, weakness, dizziness, and perioral tingling or numbness, are suggestive of Crotalinae envenomation.[1]
Erythema, edema, and tenderness to palpation at the bite site suggest Crotalinae envenomation. [Figure caption and citation for the preceding image starts]: Localized edema following Crotalinae envenomationFrom the personal collection of Dr Michael Greenberg; used with permission [Citation ends].
The leading edge of the affected local area should be serially marked every 15 to 30 minutes to assess for symptom progression. The circumference of the bitten limb should be measured above and below the snakebite for later comparison and determination of subsequent swelling.[20]Signs of shock such as hypotension, tachypnea, tachycardia, and altered mental status may be present.[1] Petechiae, ecchymosis, hemorrhage, and hemorrhagic bullae may also occur following Crotalinae envenomation.
Signs of Crotalinae envenomation generally develop over a period of minutes to hours. Severe envenomations may result in symptoms within 15 minutes of exposure, while less severe envenomations may not be apparent for hours. Generally, Crotalinae envenomations will produce symptoms within 8 hours of the snakebite and, if symptoms are present, may continue to progress for 12 hours.
Suspected Elapidae envenomation
Complaints of weakness or tremors, blurred or double vision, shortness of breath, or difficulty swallowing suggest Elapidae envenomation.
Bulbar paralysis with dysarthria, ptosis, dysphagia, drooling, and fixed pupils suggest Elapidae envenomation. Seizures and respiratory paralysis are serious complications.[1] Progression of paralysis to locked-in syndrome has been rarely reported following nondomestic elapid envenomations.[21]
Onset of neurologic symptoms of elapid envenomation may be within 1 hour of envenomation, or delayed for up to 12 hours. Generally, these patients should be admitted for a 24-hour period to assess for developing signs and symptoms of envenomation, and treated with antivenom as soon as such signs and symptoms develop. Allergic reactions to snake venom include urticaria and anaphylaxis.
Consultation
All snakebites should be referred to an emergency department for further evaluation, observation, and possible treatment with antivenom. The regional poison center or a board-certified medical toxicologist should always be consulted. Surgical consultation may be necessary for fasciotomy if compartment syndrome is present and does not respond to antivenom administration.
Laboratory studies
Patients with suspected Crotalinae envenomations should have the following laboratory tests performed:
Disseminated intravascular coagulation (DIC) panel (prothrombin time, PTT, fibrinogen, and D-dimer) should be tested to evaluate for DIC/coagulopathy.
CBC to evaluate for anemia and thrombocytopenia.
Blood chemistries
Creatine kinase (CK) levels may be considered in patients with severe local toxicity to evaluate for rhabdomyolysis and the risk of myoglobinuric renal failure.
Arterial blood gas may be considered in patients with signs of respiratory compromise.
Lactate testing may be used in patients with severe Crotalinae envenomation to follow the degree of microvascular hypoperfusion and guide resuscitation.
A urinalysis with microscopy may aid in the diagnosis of myoglobinuria in patients with severe local toxicity.
Patients with suspected Elapidae envenomation should have the following laboratory tests performed:
Blood chemistries.
Arterial blood gas may be considered in patients with signs of respiratory compromise.
There is no consensus as to how often the serial tests should be performed. In general, tests should be repeated if signs and symptoms of envenomation are progressing, or the patient has new complaints/findings. This would be influenced by the severity of the symptoms and effects of envenomation. For example, serial CK determinations should be performed every 4 to 6 hours in a patient with significant local effects from Crotalinae envenomation, while they would be unnecessary if there are only minimal local effects.
Imaging
Plain x-rays of the bite site should be considered to evaluate for retained foreign body. Retained snake fangs are rare following envenomation by North American pit vipers but have been reported to be visible with plain x-rays.[22][23][24] Any foreign bodies should be removed. Generally, computed tomography (CT) or magnetic resonance imaging (MRI) for evaluation of foreign body following snakebite is not necessary. If there is a high suspicion and a normal plain radiograph, CT/MRI may be performed to evaluate for retained radiolucent foreign body. Organic/inorganic material such as grass, soil, or clothing may be injected into a wound during a snakebite or during a puncture wound incorrectly identified by the patient as a snakebite. Recurrent soft-tissue infections, persistent pain, or deep-space infections should raise suspicion for retained foreign body despite negative plain radiographs.
Initial and subsequent chest x-rays should be performed in suspected Crotalinae envenomation, as pulmonary edema may develop due to cardiac failure or increased pulmonary capillary permeability, and in some cases may lead to death.[25] Initial and subsequent x-rays should be performed in patients with signs or symptoms of respiratory compromise.
Other studies
Patients with suspected Crotalinae envenomation:
Initial and subsequent ECG should be performed in patients with chest pain or palpitations. Crotalinae envenomation has been reported to cause myocardial infarction, arrhythmia, and conduction delay. A high level of suspicion for hyperkalemia should be maintained during ECG interpretation.
Compartment pressures should be measured serially when there is suspicion for compartment syndrome. Compartment syndrome should be suspected whenever significant local pain and swelling occurs. Surgical consultation should be pursued promptly in these cases.
Central venous line with central venous pressure transduction may help to guide the resuscitation of hypotensive patients. Crotalinae envenomation may cause hypotension by third-spacing with intravascular depletion or by direct cardiac myotoxicity with impaired cardiac pump function.
Continuous arterial pressure transduction may help guide the management of hypotension.
Patients with suspected Elapidae envenomation:
A negative inspiratory force test will assess for weakness of the muscles of respiration.
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