Cobra Envenomation Treatment & Management

Prompt movement of a victim to a medical facility capable of rendering advanced care, including airway support and antivenom administration, is critical. The following are additional pre-hospital considerations. Addressing these should be weighed with delays in obtaining a higher level of medical care.

Species Identification

Make every effort to specifically identify the envenoming species; this aids further management and determination of the proper antivenom to be administered.

• Wild snake bite. Identification may be equally problematic and important, particularly if there is more than one antivenom option for the region. Attempts to capture or kill the snake could result in additional bites or delay in transporting the victim to medical care. If possible, a digital photo of the snake may be a better choice. If the snake is killed, it must be handled with care as it may have a prolonged bite reflex after death that could lead to additional envenomation. Knowledge of the snake fauna of an area and habits of the various species may help in identification. If available antivenom is polyspecific, covering all cobras in the region, precise species identification becomes much less important. Fairly accurate ELISA tests for identification of snake venoms in wound aspirate, serum, urine, and other body fluids have been developed but are not generally available in regions where cobras live.
• Captive snake bite. If the bite occurs in a research or zoo setting, the cage identification card should be brought to the hospital. If available, species-specific antivenom should be sent with the patient. If a captive cobra in a private collection inflicts the bite, identification may be more straightforward. Unfortunately, tremendous controversy exists among experts regarding taxonomy of cobra species and becomes amplified in the lay herpetoculturist community. A private collector who presents after being bitten by his or her captive "Thai cobra" may have been envenomed by any 1 of at least 3 different species, each with different clinical consequences. Expect a variety of physiologic abnormalities and enlist professional help (eg, from a local zoo) to obtain prompt, accurate identification of the snake.

Pressure Immobilization

Arterial tourniquets is generally not recommended and has caused loss of limb function. A completely occlusive tourniquet might be considered when a victim has been bitten by a highly toxic snake, such as a cobra, and travel time to medical care is short. The efficiacy of however is unproven and additional harm may occur.

An alternative wrap is the pressure immobilization technique, developed in Australia. Similar techniques has been shown to be helpful in delaying systemic absorption of venoms primarily by reducing lymphatic spread of venom (main mechniasm of spread), although high quality studies are lacking to substantiating efficacy. An appropriate approach to studyiung efficacy requires measurement of blood venom levels before and after removal of wrap to suggest the intervention limited systemic spread of venom. One small prospective study of bites in Burma demonstrated efficacy, however in Russell viper bites. ^[17]

An elastic compress (eg, Ace wrap, clothing, crepe bandage) is wrapped rapidly around the affected extremity, beginning distally and progressing proximally to encompass the entire limb. The compress is as tight as one used for immobilization of a severe ligamentous sprain. The extremity can also be splinted to limit movement and kept at heart level. The patient should limit movement as much as possible. Some studies show that individuals often underestimate the degree of tension required for the wrap to be effective, and, even with intensive training, are usually unable to apply the technique correctly. Bandages and wraps often become loose as well. ^{[18, 17]}  Defer this technique for venomous bites known to cause local necrosis (such as with African spitting cobras) with cytotoxic and hemotoxic effects, as local tissue damage may be increased with its use. ^[19]

The Australian pressure immobilization technique. This technique has been shown to be helpful in delaying systemic absorption of elapid venoms, but its use in cobra bites remains controversial. A broad pressure bandage is immediately wrapped, beginning distally (illustration 1 of 5), around as much of the extremity as possible (illustrations 2 and 3). No effort should be spent removing clothing prior to bandage application. The bandage is wrapped snugly, as for a severely sprained ligament. A splint (or sling when applied to the upper extremity) is then placed (illustrations 4 and 5), and the victim is carried from the scene. The victim should expend no effort in getting to definitive care. Pressure immobilization should remain in place until the victim has reached medical care. The doctor will decide when to remove the bandages. If venom has been injected, it will move into the bloodstream quickly once the bandages are removed. The doctor should leave the bandages and splint in position until appropriate antivenom is available. Used with permission from Commonwealth Serum Laboratories.

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The Australian pressure immobilization technique, illustration 2 of 5. A broad pressure bandage is immediately wrapped, beginning distally (as shown above), around as much of the extremity as possible. No effort should be spent removing clothing prior to bandage application. The bandage is wrapped snugly, as for a severely sprained ligament. Used with permission from Commonwealth Serum Laboratories.

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The Australian pressure immobilization technique, illustration 3 of 5. A broad pressure bandage is immediately wrapped, beginning distally (as shown above), around as much of the extremity as possible. No effort should be spent removing clothing prior to bandage application. The bandage is wrapped snugly, as for a severely sprained ligament. Used with permission from Commonwealth Serum Laboratories.

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The Australian pressure immobilization technique, illustration 4 of 5. A splint (or sling when applied to the upper extremity) is then placed and the victim is carried from the scene. The victim should expend no effort in getting to definitive care. Pressure immobilization should remain in place until the victim has reached medical care. Used with permission from Commonwealth Serum Laboratories.

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The Australian pressure immobilization technique, illustration 5 of 5. A splint (or sling when applied to the upper extremity) is then placed and the victim is carried from the scene. The victim should expend no effort in getting to definitive care. Pressure immobilization should remain in place until the victim has reached medical care. Used with permission from Commonwealth Serum Laboratories.

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Local Wound Considerations

Avoid cooling measures and ice application. They have been associated with increased necrotic complications.

Use of a mechanical suction device is unlikely to return any significant amount of venom and should be avoided. It may also increase local tissue damage if a necrotizing venom is involved. 

Eye Irrigation

If venom is spit into the eyes, immediately and copiously irrigate them with any bland fluid, such as water, saline solution, or milk. ^[20]

Initial Evaluation

All persons who have been bitten by a cobra should be presumed to have received a severe envenomation and should be managed accordingly. This includes close monitoring of cardiorespiratory status and expedited efforts to locate and procure appropriate antivenom for the offending species. ^[21]  Assess the patient's airway and breathing. Aggressively manage any signs of impending respiratory failure with endotracheal intubation to prevent aspiration. Institute cardiac and pulse oximetry monitoring and closely monitor the patient's vital signs. Consider starting at least 1 large-bore line with normal saline or Ringer's lactate.

Antivenom

Antivenom is the only proven therapy for significant snakebites. ^[22]  They consist of antibodies produced and collected from an animal donor (typically horse or sheep) that have been introduced to sub-lethal doses of venom. Monovalent antivenom consist of antibodies that neutralize venom from only one species, while polyvalent neutralize multiple - typically of multple regional snake species. This becomes useful when the exact species in question is unknown. As expected, treating with a monovalent antivenom specific to the biting snake species is typically more effective than treating with a polyvalent antivenom - which may have decreased antibody concentration specific for the offending venom or whose antibodies have partial cross-reactivity against the offending venom. Repeated and higher doses of less-specific polyvalent antivenom also poses a higher risk for anaphylaxis and anaphylactoid reactions. ^[23]

Roughly 20 laboratories in Africa, Asia, and Europe produce antivenoms. Quality and efficacy of antivenom varies, and no international standards of purity or effectiveness exist. In the United States, none of the available cobra antivenoms have FDA approval. In general, antivenoms are largely ineffective in preventing or ameliorating necrosis caused by envenomation. Additionally, manufacturers often recommend refrigerating antivenom to improve their stability and storage duration. Costs and logistics may limit availability of antivenom in certain regions of the world.

Antivenom can be started according to the manufacturer's instructions regarding route and dose. Prior to administering, some manufacturers advise an intradermal skin test of the antivenom to gauge an acute reaction; however, this has not been substantiated and unpredictive of anaphylactic/anaphylactoid reactions and will delay administration of the antivenom. Multiple vials of antivenom may be required for effective treatment.

Given venom variability, antivenom produced in the country of origin of the offending species is preferred. Before administration, intravascular volume should be expanded using crystalloids such as normal saline or Ringer's lactate unless some contraindication (eg, congestive heart failure) is present. Pretreatment with antihistamines (H1 and H2 blockers) can be considered, though their efficacy at preventing adverse reactions to antivenom is unproven. Epinephrine and steroids (eg methylprednisolone 1g) should be immediately available for treatment of an anaphylaxis or anaphylactoid response to the heterologous serum.

Table of antivenom choices for cobra bites. As antivenom manufacturers come and go in the market, choices in this list may or may not be available. Consultation with regional poison control centers, which have access to the Antivenin Index, may help identify and locate an appropriate product for use.

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If the envenomating species has been determined, a resource, such as the Antivenom Index (published and maintained by the American Association of Zoological Parks and Aquariums and the American Association of Poison Control Centers), can be accessed by calling a regional poison control center or the Arizona Poison and Drug Information Center (from outside Arizona, 520-626-6016; from Arizona only, 800-362-0101). This document lists the preferred antivenoms available for most medically important venomous snakes around the world and has information about where these sera can be obtained in the United States (usually zoos or serpentariums). Once the antivenom is located, the physician may need assistance from the police or military to facilitate its rapid transport.

Venoms of the African spitting cobras are among the most difficult to neutralize by nonspecific antivenoms. Notechis (Australian tiger snake) antivenom proved effective in animal experiments against 9 of 11 cobra venoms, exceptions being ringhals and Chinese cobra venoms. Apparent effectiveness of tiger snake antivenom in clinically treating cobra bites has been shown in a few cases.

Evaluation of Bite Injury

If the patient arrives with some device applied in an attempt to limit spread of the venom, such as a tourniquet, constriction band, or pressure device, quickly assess the patient to determine if any evidence of systemic toxicity is present.

Assess the presence of distal pulses below the ligature. If symptoms are present and antivenom is available, start the antivenom before removing the device. If symptoms are absent and antivenom is available, remove the device and observe the patient closely for symptoms or signs of toxicity. If signs of envenoming occur, administer antivenom promptly.

If the tourniquet is totally occluding arterial flow, and there will be a delay in obtaining antivenom, apply a more loosely fitting device, such as the Australian pressure immobilization technique (see Prehospital Care), and then remove the tourniquet. A more loosely fitting device is appropriate to prevent the release of acidotic, hyperkalemic blood and venom into the central circulation as the tourniquet is released.

Evaluation of Eye Injury

When applicable, initiate and continue irrigation of the eyes with saline. Applying several drops of a topical ophthalmic anesthetic agent may reduce pain and aid in irrigation. The topical use of 1:1000 epinephrine solution is reported to relieve pain promptly. A fluorescein-aided slit lamp examination helps to find evidence of corneal damage. A brief course of topical ophthalmic antibiotics and preservative-free lubricating drops may be prescribed.

Admit cobra snakebite patients to closely monitored settings.  Monitor even asymptomatic patients for 24 hours, as delayed signs and symptoms may occur. 

Respiratory paralysis leading to mechanical ventilation may still be required, either because of the inefficacy of the administered antivenom and/or the delayed nature of the paralysis. Neurotoxic effects will however spontaneously resolve even with failed antivenom treatment. Patients requiring mechanical ventilation will typically see their respiratory paralysis resolved within 1 to 4 days, ocular muscles within 2 to 4 days, and full motor function in 3 to 7 days. Prolonged cases of paralysis resolution have been noted requiring up to 10 weeks after envenomination of mechanical ventilation. ^[1]

Serum sickness may occur as a reaction to proteins in received antivenom after 5 to 10 days. Patients should be educated on signs and symptoms, and instructed to return to a medical provider if they are encountered. The patient should promptly initiate systemic corticosteroids, diphenhydramine, and analgesics.

If necrosis occurs, initiate standard, conservative wound care (eg, cleansing, splinting, debridement as necessary). Secondary bacterial infections may occur and are usually caused by gram-negative bacilli, such as Proteus, Pseudomonas, and Enterobacter species. ^[24] Initial antibiotics should cover gram-positive and gram-negative organisms. Culture results should determine use of further antibiotics. Occasionally, debridement, amputation, or grafting of tissue is required.

See the list of consultations below:

• Toxicologist or expert in snake envenomation

• Regional poison control center

• A local zoo or museum - May be able to assist in species identification and may have appropriate antivenom in stock

• Ophthalmologist  - Should evaluate any patient who has eye exposure to spitting cobra venom

• General surgeon or plastic surgeon for follow-up care of necrotic wounds, potentially requiring serial debridements

For a comprehensive treatment overview, from first-aid care to in-hospital medical management, review UCSD Toxicology's approach to a king cobra (Ophiophagus hannah) bite.

Professional snake keepers should use standard safety techniques (eg, locked cages, trap boxes, protective eyewear) when dealing with cobras and other species that spit venom.

Amateurs should refrain from keeping exotic venomous snakes in their collections. If they keep such snakes, they should know the specific species they keep, the appropriate antivenom type, and where it can be obtained in an emergency. Preferably, amateurs should maintain their own supply of appropriate antivenom, but this may be difficult (due to regulations related to importing foreign antivenoms into the country) and expensive.

Travelers in regions where cobras are indigenous should wear protective clothing (long pants and footwear), avoid areas where snakes seek cover, and know the location of the nearest source of medical care in case they are bitten.

Patients with necrosis need continued outpatient management of their wounds and should be warned about the signs and symptoms of infection. Continued outpatient physical therapy may be necessary.

Patients who received antivenom should be aware of the signs and symptoms of delayed serum sickness and should return if they develop.

Patients who have experienced acute ophthalmia following spitting cobra venom exposure should have outpatient ophthalmologic follow-up to monitor for complications such as uveitis or corneal ulceration.