General Anaesthesia

Why does my pet need to be anaesthetised?

Many of the procedures we need to carry out cannot be performed on a conscious or sedated patient because they will not be relaxed enough. Unlike humans, we cannot ask our patients to place themselves in specific positions required for X-rays, scanning or surgery. Although we can use local anaesthetics to numb a surgical site, administering the local anaesthetic in itself may cause discomfort and it does not prevent animals from moving during the surgical procedure.

What is an anaesthetic?

There are several types of anaesthesia, but all of them lead to a loss of sensation. General anaesthesia is a state of reversible unconsciousness when your pet will be ‘asleep’ under the anaesthetic. Anaesthetic drugs injected into veins or anaesthetic gases breathed into the lungs are carried in the bloodstream to the brain. These drugs stop the brain recognising messages from nerves in the body. This is different from the unconsciousness than occurs in injury or disease.

What do I need to do to prepare my pet for surgery?

  • You will need to fast (starve) your pet overnight – your pet should have their normal meal the night before admission (unless otherwise instructed), but should have no further access to food after this. However, he or she should have free access to water until you leave the house to come to the surgery.
  • Cats should be kept in during the night before the procedure to prevent them helping themselves to food from elsewhere and to make it easy to find them in the morning!
  • Take your dog for a walk in the morning to allow him or her to empty the bladder and bowels.
  • Watch out for any signs of illness not related to the procedure which is about to be carried out on your pet, and let the vet or nurse know if you have any concerns.
  • Have a note of your pet’s current medication, including over-the-counter preparations, and make sure that the vet or nurse knows about these at the time of admission.

What happens after my pet has been admitted?

The anaesthetic drugs to be used will be chosen according to the procedure that is being performed and the medical history and findings on physical examination of your pet. Your pet will then be injected with pre-anaesthetic medication (a ‘pre-med’).

After an appropriate amount of time, an intravenous catheter will be placed, to allow administration of drugs and fluids during the procedure. For most pets we will then use this catheter to inject an intravenous anaesthetic agent which allows us to place a tube (called an endotracheal tube) down the patient’s wind pipe (trachea). During most of the procedure, further anaesthetic drugs are administered as a gas through this endotracheal tube.

How do you keep my pet safe during general anaesthesia?

Our aim is to provide the best care for your pet at all times, including during general anaesthesia. To this end, North Downs Specialist Referrals is fortunate to have a team of dedicated anaesthetists, including two recognised, accredited anaesthesia Specialists, who are on hand to supervise and assist with each anaesthetic procedure, as required.

For the whole duration of general anaesthesia, your pet will be connected to an anaesthetic machine, which delivers a mixture of anaesthetic gas and oxygen. The amount of gases and the type of anaesthetic circuit used is adjusted to the needs of each individual patient.

While your pet is anaesthetised, he or she will be closely observed throughout the procedure by veterinary anaesthesia staff and/or highly trained, qualified nursing dedicated to the one-to-one care of your pet. In addition, specialised monitoring equipment is used to keep a close watch on your pet’s progress. The monitoring equipment used depends on the surgical procedure, type of anaesthesia used, and medical history of each patient.

At NDSR, we use monitoring equipment which measures:

  • heart rate and rhythm (electrocardiography or ECG)
  • pulse rate
  • respiratory rate
  • body temperature
  • blood pressure
  • oxygenation of blood (called pulse oximetry)
  • carbon dioxide level in the breath (called capnography).

The staff involved will also monitor your pet’s pulses, gum (mucous membrane) colour, position of the eye and reflex activity to determine the depth of anaesthesia. All the readings obtained and any observations are recorded every 5 minutes on an anaesthetic record chart.

When the surgical procedure is complicated or for a pet with a higher risk of undergoing anaesthesia, more information about the patient is required to make sure that he or she remains safe and comfortable. To obtain this information we use more advanced monitoring techniques, including:

  • ‘invasive’ arterial blood pressure measurement (using a cannula which is placed in an artery to directly measure the arterial blood pressure, rather than using a cuff)
  • central venous pressure monitoring (measuring the blood pressure in the veins deep inside the body)
  • measuring the level of muscle relaxation (called neuromuscular blockade)
  • measuring of breath (spirometry)

All this information is important, and it helps us to anticipate potentially significant problems almost before they occur. If there are any concerns, an anaesthetist can take the necessary actions to bring all the parameters back to the normal levels as promptly as possible. The adjustments required under such circumstances may include giving additional injections, more pain relief, supplementary intravenous fluids or oxygen. If there is any problem with the breathing, your pet will be connected to a unit which automatically inflates the chest (mechanical ventilation) to make sure enough oxygen is provided.

We will take special care to make sure your pet is warm during whole procedure and on recovery. Under general anaesthesia, the brain does not control body temperature and patients can lose heat very quickly. It is especially important to maintain body temperature in small, young and short-haired animals. We use a range of warming devices to prevent heat loss – in the operating theatre our patients are placed on special heated beds with in-built sensors, and intravenous fluids are heated by fluid warmers.

When a procedure has finished, the anaesthetic gas is switched off and the patient is given oxygen until he or she starts to recover and wake up. Most pets recover consciousness very quickly, although older animals or those who have had a longer anaesthetic may recover more slowly.

During recovery, your pet will be taken to a warm and comfortable bed in the kennels (or our Intensive Care Unit if required) and will be carefully monitored until he or she is fully awake.

How is my pet prevented from feeling pain?

Most of our patients undergoing anaesthesia will receive at least two types of painkillers. The most commonly used are the morphine type drugs and drugs from the aspirin family (the so called ‘non-steroidal anti-inflammatory drugs’ or NSAIDs). We also use different techniques and medications, taking into consideration your pet’s history and the procedure he or she is having.

What will my pet be like after coming home from North Downs Specialist Referrals?

If your pet is discharged on the day of surgery, he/she will probably be a little sleepy. Strong painkillers will have been given and these will last some time. You should offer your pet some light food (e.g. boiled chicken or fish and rice) and water, but do not expect him or her to have a normal appetite. The effects of the anaesthetic will wear off over the next few days. Please look out for any signs of pain or discomfort and contact the hospital if you are at all concerned.

What can I do for my pet after a general anaesthetic?

  • Provide him/her with a bed in a quiet, warm area.
  • Do not let cats go out until the next day, if at all possible, as their balance may not be back to normal.
  • Take your dog out to the garden or for a very short walk to allow him/her to pass urine, but do not let him/her off the lead.
  • Follow the instructions provided by your vet for medication and general care which is specific to his/her condition.


If you have any concerns at any stage after your pet’s operation, please do not hesitate to contact us.

Arranging a referral for your pet

If you would like to refer your pet to see one of our Specialists please visit our Arranging a Referral page.