Treatment of Snake Envenomation in Dogs and Cats

In our previous articles on snake envenomation, we’ve discussed the mechanisms of snake envenomation as well as the important tests that can be used during the diagnosis of snake envenomation. Now we’ll discuss possibly the most important, and certainly the most life-saving, aspect of any suspected snake bite: the treatment of snake envenomation in dogs and cats. Although most of us are familiar with antivenene, there are many more elements of treatment to maximise your patient’s chances of survival. So what can you use in your clinical toolkit to provide the best possible treatment for your next snakebite patient?

Treatment of Snake Envenomation – Emergency Patient Management

As soon as the patient comes through the clinic door, you’ll need to perform several urgent steps without hesitation. Whether they’re bright and walking or crashed and being carried, these life-saving steps include: 

• Intravenous catheter: Immediate placement of an intravenous catheter upon presentation
• Intubation equipment: Ensure intubation equipment is set up and ready to be used at any moment. Rapid deterioration can occur within 2 – 5 mins from clinically normal to absolute respiratory paralysis
• IV fluids: Manage haemodynamic abnormalities by administration of shock fluid boluses of crystalloids if necessary. Continue to maintain fluids at 1x maintenance at minimum
  • Caution should be exercised in patients with pre-existing cardiac conditions, or where large volumes of crystalloids are given with antivenin administration
  • More information on fluid therapy can be found via the Fluid Therapy Protocol on VetAPedia
• Adrenaline: Pre-medication prior to anti-venin administration is not recommended, though adrenaline should be on hand if an anaphylactic reaction is seen
  • NB: Premedicant administration has been shown to not prevent anaphylaxis
  • Adrenaline 0.01mg/kg IV or IM (i.e. 1ml/10kg IV for a reaction followed by a CRI at 0.05mg/kg/min if required to control hypotension)
• Snake Antivenene: prepare to administer antivenene to the patient 

These first moments of patient presentation can be critical in the treatment of snake envenomation. Ensure you have all necessary equipment and medication prepared for when the patient arrives. The next step is the administration of snake antivenene in order to neutralise any circulating venom.

Treatment of Snake Envenomation – Antivenene Administration

Antivenene (also called antivenom or antivenin) is arguably the most important medication involved in treating the snake bite patient. Products are available in either monovalent (single species) or multivalent (multiple species) varieties. Multivalent tiger/brown snake antivenene commonly used in Australian veterinary practice. Dose for both dogs and cats is as follows:

• Dog & Cat Dose: Dilute a single vial of antivenene 1:1 with saline and give over 20 mins
• Brown Snake Envenomation Dose: all known Brown Snake envenomations are recommended to receive 2x vials of multi Tiger/Brown antivenene due to their coagulopathic tendencies and to neutralize the venom

Neutralization of all venom occurs with 4000- 8000 units of Tiger/Brown antivenene in high serum levels, so the current recommendation is to administer 2 x 4000 units of antivenene and not to repeat the SVDK. The patient’s coagulopathic, myotoxic and haemotoxic effects should be monitored, but these should not be used as triggers for further antivenene administration. If the patient remains coagulopathic WITH clinical bleeding (determined by clinical and de novo bleeding, or by prolonged PT/aPTT or ACT), fresh frozen plasma is indicated. The dose for FFP is 10-20mL/kg given over 2-4 hours (care should be taken to avoid volume overload).

Treatment of Snake Envenomation – Critical Monitoring and Supportive Care

Supportive care is a critical aspect of any snake envenomation patient, as antivenene certainly has the capacity to neutralise snake venom, but won’t counteract any damage that has already been caused. Being able to provide ideal supportive care to your patient and support their circulatory, renal, respiratory, and even gastrointestinal systems will significantly improve their prognosis in most cases. Here are several supportive care methods to consider:

Intravenous Fluid Therapy

• For most patients, an isotonic crystalloid solution with electrolyte supplements as needed (e.g., KCl, KPO4, MgCl) is the most appropriate choice.
• Fluid should be administered at 1-2x maintenance to ensure diuresis
• If cardiovascular compromise is present at shock rates of 10 – 20mL/kg, titrate the fluid rate to effect
• Return to maintenance rates once adequate mean arterial pressure and urine production can be established
• Fresh frozen plasma should be given at 10-20mL/kg over 2 – 4 hours as needed for treatment of coagulopathies which persist after venom has been neutralised
  • Administration rate of crystalloid fluids should be reduced commensurately during administration

Respiratory Support

Envenomation with procoagulant venom and neurotoxins may result in hypoxaemia by a number of mechanisms including:

• Pulmonary Haemorrhage: this is a severe and immediately life-threatening development of brown and tiger snake envenomation. Early signs may include haemoptysis only. Treatment goals should be directed to maintaining adequate oxygenation whilst neutralizing the venom, and then reversing the coagulopathy as quickly as possible. Early and adequate neutralization of venom and identification of a consumption coagulopathy is essential. The prognosis for this clinical development, in the author’s opinion, is grave.
• Aspiration Pneumonia: Megaoesophagus is also recognized in canine patients envenomated by Tiger snakes. This clinical entity reportedly may persist for up to 6 weeks even after resolution of generalized peripheral
  neuropathy. Aspiration pneumonia is a well-known risk of this problem. Measures must be taken to prevent aspiration such as suctioning the oropharynx if saliva pooling occurs. Intubation under general anesthesia may also be required if severe loss of gag reflex is present. If an animal can be intubated without anaesthetic agents, then mechanical ventilation is usually necessary.
• Hypoventilation: this results from profound respiratory muscle paralysis. Monitoring blood gas analyses is helpful in tracking a trend towards respiratory failure (PCO2 > 60mmHg) due to hypoventilation. Venous blood gas is as useful in this setting as collecting an arterial sample is contraindicated in coagulopathic animals. PcvCO2 is approximately 4-5mmHg higher than arterial blood. Peripheral venous CO2 is approximately 3 – 8mmHg above arterial.

Treatment of Hypoxaemia

• Oxygen Supplementation
  • Oxygen can be administered by nasal oxygen line (care in coagulopathic patients) or oxygen cage (delivers FiO2 of 40—60%)
  • Administer oxygen by insufflation in patients which are intubated
• Mechanical Ventilation
  • Appropriate for patients demonstrating either hypoventilation (PCO2>60mmHg) or hypo-oxygenation (determined by arterial blood gas if obtainable, or by persistently low pulse oximetry (SpO2<90%))
  • Length of ventilation requirement is variable and may be dependent on factors such as reversibility of paralysis. Paralysis due to pre-synaptic toxins (eg: tiger, brown, black, taipan), are more difficult to reverse than those caused by post-synaptic neurotoxins (e.g., copperheads).
  • In hypocapnoeic patients with normal lungs, select the least aggressive ventilator settings.

Medications

• Mannitol (1-2mg/kg/min) if pigmenturia is present as it is a proximally acting diuretic, a potent renal vasodilator and a potential reducer of haeme iron units induced oxidant stress
• Sodium bicarbonate therapy can be considered to alkalinise the urine and promote excretion of haeme products. It may also be of use in treating the accompanying metabolic acidosis
• Frusemide should be given if anuria or oliguria exists; 1-2mg/kg to a total of 4mg/kg to promote diuresis
• Sedatives may be of use with anxious animals developing lower motor neuropathies
  • Butorphanol CRI at 0.04-0.4mg/kg/hr
• Analgesia with a mu agonist if significant rhabdomyolysis is present.
  • Methadone 0.1-0.3mg/kg SC q4hrs 
  • Fentanyl CRI at 2-4ug/kg/hr
• Prokinetic agents may be helpful where megaoesophagus exists
  • Metoclopramide CRI at 0.04-0.08mg/kg/h or 1-2mg/kg/day
• Consider gastric protectants to increase gastric pH in anticipation of aspiration, or in managing oesophageal ulceration secondary to reflux
  • Esomeprazole 0.7-1.0mg/kg IV q24hrs

Nutrition

Early enteral nutrition should be instituted as soon as the gag reflex is normal and the animal is able to swallow. If the animal remains paralysed and a gag reflex remains absent, consider the use of an appropriately selected feeding tube. This can be one of the following options:

• Nasogastric tube placement for severely affected cases for gastric decompression or feeding
• Oesophagostomy tube for cats or small dogs
• Gastrostomy tube for documented tiger snake-induced megaoesophagus may be warranted

Nursing Care

Lastly, some snake bite patients may be hospitalised for a considerable length of time and will require close attention to their supportive nursing care. This includes aspects such as:

• Patients should be kept warm and have their temperature measured regularly
• Provide appropriate padding and soft bedding to prevent pressure sores and contusions
• Elevation of head to 30°
• Ensure adequate analgesia and reevaluate pain relief as required
• Physiotherapy can be quite beneficial for the mobilized patient
• Eye care and regular application of artificial tears for the paralysed patient
• Bowel and bladder care (placement of urinary catheter and closed collection system is ideal to ensure urine is produced at 1-2mL/kg/h (and “ins=outs”)

What is the prognosis of snake envenomation in dogs and cats?

• Survival range for dogs and cats with treatment ranges between 75 – 91%
• Survival range for dogs and cats without treatment for dogs is 33%, and cats is 66%
• Alkaline urine reduces the incidence of possible nephrotoxicity
• Delayed time in getting to a hospital following Tiger snake envenomation increases mortality in dogs

Even with the most careful preparation, the treatment of snake envenomation in dogs and cats can be a challenging clinical scenario. Even for the most experienced veterinary professionals! Want to be as prepared as possible for your next snake bite case? Download the free Snake Envenomation Protocol that you can easily print out and refer back to in your clinic.

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