Pet Factsheets

All about anaesthesia

Anaesthesia is a subject that often worries many owners, but many pets will undergo an anaesthetic during their lifetime. It is important to therefore have an understanding of the subject.

What is anaesthesia?

Anaesthesia is defined as 'insensitivity to pain, especially as artificially induced by the administration of gases or the injection of drugs before surgical operations'.

A general anaesthetic is when the patient is placed into a state of unconsciousness. They are not able to feel pain, are relaxed (or paralysed if a neuromuscular blocker used) and have no memory of what happens to them when they are under general anaesthesia. This is achieved by interrupting the passage of signals along the nerves. This means that any stimulation to the body doesn't get processed or recognised by the brain. However, there are a number of kinds of anaesthetics and in some - such as local anaesthetics which 'numb' a specific area - the patient is still fully conscious.

Surgical procedures, such as neutering, dentals and anything that is likely to be painful require anaesthesia. Sometimes it may be necessary to place a pet under anaesthesia for procedures when it essential that they remain still, such as CT/MRI scanning, some x-rays, and for some samples to be collected.

Local anaesthetics
These are injections, sprays or creams. They are normally used to block the sensation of pain along the nerve pathways, and can be used very successfully. Commonly local anaesthetics are used in combination with general anaesthesia to provide improved pain relief during and after surgery.

EMLA cream can be used when placing intravenous catheters or taking blood samples and is a local anaesthetic in the form of a cream that numbs the surface of the skin, meaning the animal is less likely to move at the crucial moment when the needle punctures the skin. This type of anaesthesia is not suitable for surgical procedures, since only the skin is numbed and the animal is still able to move and feel sensation.

Another example of a local anaesthetic technique is a dental nerve block, where similarly to techniques used in people the nerves supplying sensation to the teeth can be blocked to prevent pain during and after a dental procedure. These techniques are used in animals under general anaesthesia for a dental procedure to ensure that the animal stays still and receives adequate pain relief for the procedure.

General anaesthetics
A general anaesthetic places an animal into an unconscious state where they are unable to move or feel pain. This is necessary for surgical procedures to be performed.

There are many drugs and combinations of drugs that can be given to achieve anaesthesia. The choice of anaesthetic is based on many deciding factors. The age of the animal, health status and the procedure to be undertaken, are all considered when deciding on which anaesthetic to use.

Normally a premedicant is given first; this helps to relax the muscles and has a calming effect, but doesn't usually render the patient unconscious, other drugs or anaesthetic gas is needed to achieve general anaesthesia. Animals are usually maintained under anaesthesia by an anaesthetic gas delivered via an endotracheal (ET) tube placed in their trachea (windpipe). The ET tube also ensures that the animal has a secure airway throughout anaesthesia, should an emergency occur.

Is anaesthesia safe?

Yes and no!

No anaesthetic is 100% safe, 100% of the time, and no two animals ever react the same to an anaesthetic, but anaesthesia has become far more reliable and safe over the last decade. Recent evidence suggests that the death rate during anaesthesia in healthy dogs is about 1 in 1800 dogs and in healthy cats it is about 1 in 900 cats, suggesting that the risks of anaesthesia are greater in cats than dogs. The risk of death increases in patients that are unhealthy.

Ways that risks of anaesthesia are minimised include:

  • Constant monitoring by trained staff when the pet is under anaesthetic.
  • Minimising stress, before and after anaesthesia.
  • Keeping patients warm before, during and after surgery.
  • Providing medication for pain.
  • Placing an endotracheal tube to aid breathing and an intravenous catheter to supply fluids.
  • Use of safe anaesthetic drugs.

Lowering the risk however doesn't remove it completely, and there is always the risk that any patient may suffer an adverse reaction to the drugs, die under anaesthetic, bleed excessively during or after surgery, or suffer complications.

Your vet will discuss the risks involved in any anaesthetic, and the specific risks for the procedure your pet is undergoing.

Why do I need to fast my pet before an anaesthetic?

Some anaesthetic agents can make pets feel nauseous. It is really important that your pet does not vomit whilst under anaesthetic or on recovery because there is a risk that they will inhale some of the vomit. Dogs and cats should not have anything to eat within 6-12 hours of an anaesthetic so that their stomach is empty. If you think your pet may have had access to food you must let your vet know when you take your pet in for an anaesthetic and your vet will decide whether to reschedule the procedure.

Will my pet need special care following an anaesthetic?

Your vet will want to keep your pet in the hospital until they are sure that it is fully recovered from the anaesthetic. Once your pet gets home they will probably want to rest quietly for 24 hours but should be eating and drinking normally by then. If your pet is uncomfortable following surgery they will be reluctant to eat, and therefore it is important to provide good pain relief to ensure a rapid recovery. Speak to your vet if you are concerned that your pet is uncomfortable, restless or reluctant to eat.

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