Anaesthetics - the what why and how


by Dr. Francesca Matthews


What is Anaesthesia?


Anaesthesia is the word given to the loss of feeling or sensation in a part or the whole of the body. If you have been out in the cold with no gloves on for a period of time, you feel a sensation of numbness in your hands. This is a type of temporary anaesthesia.

Veterinarians use drugs to induce anaesthesia in your pets to enable them to perform what would otherwise be painful procedures.

Most commonly, veterinarians administer general anaesthetics. This means they induce unconsciousness in you pet so there is no feeling of pain or other sensation and there is also memory loss. That is, your pet will awake from the anaesthetic with no memory of what happened between losing consciousness and regaining consciousness at the end of the procedure.

Local anaesthesia is sometimes used to induce anaesthesia in a localised area. This may be used in combination with a sedative, a general anaesthetic or alone. Local anaesthesia is similar to what you would receive if you had to have a small wound stitched up on your own leg by your GP for example. 

Sometimes rather than a full general anaesthetic for less invasive procedures, your veterinarian may advise that they will use a deep sedation. These work well for non-invasive procedures, where full relaxation is not required.  Veterinarians may used sedation in combination with local anaesthetic for situations such as minor stitch ups.

Our veterinarians will advise you on the best form of anaesthetic for your pet.  It will vary depending on your pet and the procedure to be performed.



Why do my pets need anaesthetics?


Anaesthesia is used commonly in veterinary practice to assist veterinarians to be able to perform procedures on our pets without them feeling pain but also to increase compliance. As you would completely understand, while it is possible to tell a human to sit still while the doctor injects local anaesthetic around a wound or stitching up, or a dentist comes at you with dental instruments, your pet is not able to be instructed in the same way. Even the most compliant pet will refuse!

Common procedures where anaesthesia is used include


  • Desexing - read about desexing in dogs, cats, rabbits
  • Dentals - read about dental care in dogs, cats, rabbits
  • Flushing out cat bite abscesses
  • Bone surgery
  • Abdominal surgery - when we open up the abdomen (which houses the stomach, intestine, liver and many other organs) to perform many different procedures. Examples include: removing items like corn cobs or stones from your pet's stomach that they may have eaten, mineral stones in the bladder (these develop when the minerals begin to clump together, becoming crystals and then stones), and organs that have tumours in them.
  • To enable us to take radiographs (x-rays)


There are of course many more reasons for using anaesthetics.


How safe are anaesthetics?

While we'd love to be able to say that anaesthetics are 100% safe, the reality is that there is an inherent risk associated with inducing an animal into a state of unconsciousness, which is what occurs when we give anaesthetic.


The good news is that the risk is very low. For a normal healthy animal undergoing an elective procedure the risk of death is approximately 1:200,000. In animals that are older or younger and/or have pre-existing conditions the risk may be slightly higher.

Veterinary anaesthesia is following closely with medical anaesthesia, which means that new developments in the human field are implemented quickly into the animal field, if they are suitable for animals.

Prior to an anaesthetic being performed on your pet, our veterinarians will discuss the planned procedure and requirements for anaesthesia. They will outline the risks and benefits of the anaesthetic and the procedure. They may advise further testing prior to the procedure to help in determining any additional risks your pet has. Once you have discussed this all with our veterinarian and are satisfied that the benefits outweigh the risks, you will be asked to sign a consent form which confirms that you understand the procedure and the inherent risks.

Our veterinarians are able to reduce the risks further by:

  • Using pre-anaesthetic blood testing - discuss with your vet whether this is right for your pet
  • Carefully selecting the best anaesthetic for your pet - this is based on a number of different factors
  • Ensuring they have a qualified veterinary nurse dedicated to monitoring your pet's anaesthetic while they are operating
  • Using additional monitoring equipment such as blood pressure monitors and pulse oximeters that measure oxygen saturation
  • Although we can't give 100% guarantees, veterinary anaesthesia is very safe and the benefits in nearly all cases outweigh the risks. Make sure you talk through with your veterinarian any specific concerns you have, to ensure that you have peace of mind prior to signing the consent form.


What is pre-anaesthetic blood testing and should I do it?

Pre-anaesthetic blood testing helps to give a picture of what is going on inside the animal. The tests are focussed on orgnas that can increase anaesthetic risk if not functioning to their full potential. Kidney and liver function are examples of organs that are required to excrete anaesthetic agents. If small deficits are noted our veterinarians might change the anaesthetic or fluids protocol. In high risk animals or animals that have been ill for sometime, they will more often than not have had full blood panels done and these include all of the above, as well as additional tests. The information from these will be used in making anaesthetic (and other) decisions.


Review the separate article on blood testing.

Should you have this done?


Always discuss this in conjunction with our veterinarians prior to making a decision. If money is no object, then a pre-anaesthetic blood screen, including measurement of oxygen carrying capacity is ideal. However, in most cases we have to make some decisions based on risk analysis. If the risk is deemed to be low, then the decision between you and our veterinarian might be to elect not to do pre-anaesthetic blood testing. If there is any possible risk, due to your pet's history or your pet is now considered elderly, then pre-anaesthetic blood testing would also be highly recommended.

In most cases we will find normal blood results, but this helps to give peace of mind going into anaesthetic that the internal organs are functioning optimally. If a normal result is discovered, it also provides a baseline for our veterinarian to determine how compromised a patient may be if they come in at a later date due to illness, injury or disease.

Regular, routine blood screens also help to detect early changes that might not otherwise be detected. For example, an animal whose results for a routine blood screen normally sit at the low end of the normal range, suddenly returns a blood result with the values sitting at the high end of the normal range can be an earlier indicator of something that needs monitoring and possibly early medical intervention. Remember, your pet ages more quickly than you do, so an annual blood test is like having 7 yearly blood tests in human terms.


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