You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.

General anaesthesia is a routine procedure in veterinary practice - but, despite everyone's best efforts, sometimes things go wrong. Why ?

Administering a general anaesthetic to a patient is a complex procedure because there are many variable factors concerning the drugs to be used and the patient's condition, but it is one that veterinarians are highly skilled at, and one that many perform every day. Accurate figures on anaesthetic deaths in veterinary practice are not available - but millions of veterinary patients are anaesthetised every year and very few deaths or other serious complications are reported. So anaesthetic deaths are rare.

However, just as in human medicine, occasionally things do go wrong - and a patient may die. This is an extremely tragic time for everybody - not least for the owners and their family and friends - but also for the veterinary practice staff - veterinarians, nurses, technicians, even receptionists and other non-clinical staff are devastated by the news that an animal has not survived an anaesthetic procedure. Veterinary practices are an integral part of the local community and often everyone in the practice knows the animal and it's owners so there is sincere regret and, of course, embarrassment. 

Anaesthetics work by causing depression of the brains activity - hence they render a patient unconscious however, if the brain is depressed too much the patient can die. Many drugs used during anaesthesia (such as pain killers and muscle relaxants, as well as the anaesthetic agents  themselves) have effects on other vital organs such as the heart and the respiratory system. If cardiac function or respiratory function are compromised they too can lead to death of the patient. 

Every individual patient responds slightly differently to an anaesthetic - some require lower, and some higher doses than others to get the same effect. Some exhibit the side-effects of a drug - others do not. Overdose of an anaesthetic agent can kill a patient but veterinarians are very careful and only administer sufficient anaesthetic to get the effect that they need to perform a procedure.

Having administered an anaesthetic the animal's body has to breakdown the drug  and eliminate it - and depending upon the drug this requires normal function of the liver, and/or the kidneys. If they are not functioning properly the drug can have a greatly prolonged duration of action, and if the dose that is in circulation is very high, toxic side effects may result.

Why does death occur during anaesthesia ?

There are many reasons why death can occur during anaesthesia :

• The brain is starved of oxygen 
  • blood circulation to the brain is inadequate
    • the heart has stopped pumping enough blood to the brain
    • blood loss can result in inadequate blood volume in the circulation
    • there is obstruction of blood flow to the brain 
    • low blood pressure - not due to poor heart function
  • there is inadequate oxygen in the blood reaching the brain
    • the patient is not breathing enough eg respiratory arrest - which can be drug induced. Some drugs given to manage pain (eg morphine) can slow breathing 
    • the patient is breathing but there is inadequate oxygen in the air that the patient is breathing in. eg the oxygen supply has run out.
    • obstruction to the animals airways or lungs stopping the inhalation of air
• toxic injury to the brain or other vital organ
  • drug toxicity - overdose, or failure to eliminate the drug  from the body
  • toxins may be released from a site in the body eg histamine can be released from mast cell cancers which may be being removed surgically causing sudden anaphylactic shock and death; potent  toxins can be released from a wound site.
• tissue cells may be released from a tissue (eg a cancerous organ being handled during surgery) and get carried to a vital organ (eg the brain) where they cause obstruction of blood supply (called "embolism"). If air gets into the circulation during a surgical procedure it can have the same effect.

In the final analysis most anaesthetic emergencies are attributable to :

• Cardiovascular failure - can be drug induced
• Respiratory failure - can be drug induced
• Equipment failure
• Human error

Some patients may have a higher anaesthetic risk than others (eg patients with heart, respiratory, liver or kidney disease) and your veterinarian will perform screening tests in such circumstances and take steps before and during an anaesthetic procedure to minimise the risk of problems occurring.

Most practices now employ skilled staff to monitor patients during anaesthesia and so any problems can be identified and corrected as early as possible. 

But despite all these efforts no anaesthetic procedure can be guaranteed to be 100% safe.

Last updated : March 2008