1. Immediately remove your animal from the source of carbon monoxide and place in a well-ventilated area.
  2. Contact your veterinarian immediately.



The lethal dose of 1000ppm (0.1%) can be reached within minutes if a car is running in a closed garage. Similarly, a natural gas heater can make the air unsafe within minutes if contained in a poorly ventilated room.


Onset of signs is within minutes, depending on the dose. Clinical signs can be nonspecific and is dependent on the concentration of CO in the air, duration of exposure, ventilation present, age and size of animal and presence of any underlying diseases.

Early signs:

  • Nausea, Vomiting
  • Unsteadiness/difficulty balancing
  • Depression/drowsiness
  • Inappetence

Intermediate signs:

  • Increased heart rate (tachycardia)
  • Panting or increased respiratory rate (tachypnoea)
  • Uncoordinated and unsteady gait (ataxia)
  • Weakness
  • Deafness
  • Blindness


  • Change in mental status (animals may become depressed and stuporous)
  • Weakness/collapse
  • Irregular heart rhythm (arrhythmias)
  • Seizures
  • Coma
  • Respiratory failure/arrest
  • Death

Carbon monoxide can also harm foetuses in pregnant animals.


Carbon monoxide binds to haemoglobin molecules in the blood, impairing the delivery of oxygen-enriched blood to the body’s tissues and cells. This leads to lack of oxygen (hypoxia), cell damage and death. Carbon monoxide also causes damage to blood vessel walls, and impairs blood supply to the brain.


Treatment typically involves administration of oxygen to supply vital organs, fluid therapy to maintain blood pressure and monitoring of heart function. In animals suffering from seizures, anti-convulsants may be required.


BSAVA (2012) BSAVA/VPIS Guide to Common Canine and Feline Poisons. Gloucester: BSAVA.

Fitzgerald, KT (2006) Carbon Monoxide In Small Animal Toxicology. 2nd Eded. Peterson ME & Talcott PA. USA: Elsevier Saunders. pp.619-628