Carbon monoxide is a colourless, odourless and tasteless gas that can prove fatal if inhaled. It is a by-product of the burning of fuels such as coal, oil or gas when there isn’t enough oxygen available to enable complete combustion. Just like humans, dogs and cats can suffer from carbon monoxide poisoning if exposed so it is worth being aware of the risk. 

Table of contents

A short chemistry/biology lesson…

When a fuel such as coal, oil or gas burns in oxygen, the main by-product is carbon dioxide (CO2) but if there is insufficient oxygen available, the reaction is incomplete and carbon monoxide (CO) will form instead. It is also found in the exhaust of other sources of combustion including petrol engines, generators and lawnmowers. The reason it is so poisonous is that when inhaled, it will combine with haemoglobin within red blood cells in the place of oxygen, creating carboxyhaemoglobin. In fact, carbon monoxide has over a 200 times greater affinity for haemoglobin than oxygen does. Because the oxygen molecules are now unable to bind, the body becomes starved of this vital component of life. This leads to the condition of hypoxaemia (dangerously low oxygen levels). 

As well as this, carbon monoxide can also bind to the muscle protein myoglobin, including cardiac myoglobin, leading to possible heart complications.

How carbon monoxide poisoning can happen

Most cases of carbon monoxide poisoning in humans and animals come about due to human error; either through inefficient ventilation or incorrect installation of an appliance. A dog left in an unventilated garage for example, with a car engine running, will be exposed to fatal levels of carbon monoxide within ten minutes. A cat sleeping by a faulty heater can be chronically exposed to low levels of carbon monoxide. Levels of carboxyhaemoglobin will rise with acute exposure but also drop rapidly once the exposure has ceased.  

Animals that have been trapped in a house fire are also very likely to experience carbon monoxide poisoning, just like their owners. Firefighters are trained to treat animals and people alike.

How common is carbon monoxide poisoning?

There is very little data available on the incidence of carbon monoxide poisoning in animals and in humans, it is thought to be a hugely underdiagnosed problem. In England, there are approximately 4000 attendances per year at A&E departments with carbon monoxide related issues. Of these, 440 end up as hospital admissions. And sadly around 40 deaths per year are recorded as being due to carbon monoxide poisoning. 

Figures for dogs and cats are likely to be much less than this as sadly around 40% of deaths in humans due to carbon monoxide poisoning are due to intentional self harm. Seeing symptoms in dogs and cats can, however, help to save human life and act as an early warning system for their owners. 

Symptoms of carbon monoxide poisoning in dogs and cats

Unfortunately, because it isn’t possible to see, smell or taste the gas, there are often no warning signs of toxicity until symptoms develop. Due to its actions within the body, the symptoms all tend to be related to a lack of oxygen availability to the main organs. Most commonly, this will include:

  • lethargy
  • drowsiness
  • dizziness
  • difficulties breathing
  • coughing
  • uncoordinated movements

In severe cases, they may develop seizures, fall into a coma or even die. 

Chronic, intermittent exposure to carbon monoxide will cause waxing and waning symptoms of 

  • vomiting
  • nausea
  • flu-like symptoms
  • weakness
  • inability to exercise at normal levels
  • respiratory signs

In humans, a headache is the most often reported symptom in carbon monoxide poisoning cases. So we can only assume that dogs and cats will feel something similar. It has also been reported in dogs and cats that they can develop cherry-red skin especially around the eyes, ears, lips and nose but this may be fairly difficult to distinguish. (Even for experts – I once saw a carbon monoxide case where the gum colour led to misinterpretation of the patient’s status – Editor). 

Diagnosis of carbon monoxide poisoning

The only definitive way to diagnose carbon monoxide poisoning is to measure the levels of carboxyhaemoglobin in the blood. But this is not typically a standardly available test, certainly not at point of care. For this reason, most cases are diagnosed after a known source of exposure such as a house fire and concomitant symptoms. In-house blood tests that can look for high levels of acid in the blood and also provide information about complete organ function, will help provide evidence towards a diagnosis. 

Treatment for carbon monoxide poisoning

The priority for treating cases of carbon monoxide poisoning is to remove the animal from the source of the gas as soon as possible. It is vital that they receive oxygen therapy, ideally in 100% oxygen. As this is the only real way to try to reverse the binding of the carbon monoxide and bring about a recovery. Intravenous fluids will also be administered to help rebalance the pH level (acidity) in the blood as well as to maintain blood flow and oxygen delivery to the vital organs such as the brain. If required, medications to help support the heart function may be given and if neurological symptoms are seen, then standard anti-seizure drugs will be added. 

Prognosis for carbon monoxide poisoning

Animals will likely need to remain hospitalised for a period of time following exposure to carbon monoxide in order to ensure their blood gas balance has been restored. Thankfully, if withdrawal from the source of carbon monoxide and administration of oxygen therapy are initiated rapidly, then the prognosis for full recovery is good. 

During the recovery period, animals should be allowed to rest and not be excessively exercised. They will have the potential to become breathless quite easily. Full recovery time depends on the level and duration of exposure to the carbon monoxide; it may take from a few hours to many weeks. If the degree of exposure has been severe, there may even be lasting neurological damage. This is due to the brain being starved of oxygen. 

Prevention of carbon monoxide poisoning

Prevention of carbon monoxide poisoning simply relies on preventing exposure to the gas which is typically achieved in two ways. 

Firstly, ensure any heating appliances within the home are safely and accurately fitted by a professional who is certified to work with that fuel source. The appliances must be well maintained and regularly serviced. If any issues are found, these ought to be rectified as a matter of urgency. 

Secondly, it is very helpful to have one or more carbon monoxide detectors within the home, placed in areas of higher risk such as near cooking equipment or a boiler. These can be life saving if a leak is present, just like a smoke detector is for sensing a fire. 

A fairly rare but very serious poisoning

Overall, it is important to realise that carbon monoxide poisoning in both people and animals is rare. But because of its rapidly fatal consequences yet simple and highly effective treatment, early recognition is key. It should go without saying that if you notice something unusual about your pet or they seem to be acting out of character, it is always worth a vet check as prompt therapy can save lives. Detection of carbon monoxide poisoning in pets can also save their owners’ lives and vice versa. So don’t be afraid to speak to your veterinarian if you have any concerns. 

Further reading: