What Happens To My Pet During Anaesthesia?

Always wondered what happens to your pet during anaesthesia? Modern veterinary anaesthesia is considered very safe. The risk of losing an animal under anaesthesia while going through uncomplicated procedures, such as dental and sterilisation, is very low. The patients lost under anaesthesia are mostly emergency cases, when their conditions are already critical. However, the risk of anaesthesia can also be affected by the anaesthetic drugs used and the monitoring of our patients.


Anaesthesia works by using chemicals that act on the brain to induce a temporary state of enforced unconsciousness. During anaesthesia, your pet is unable to move and does not feel pain or other unpleasant sensations.

It is generally used in the following situations:

  • procedures that involve significant pain or unpleasant sensations, such as surgery, dental scaling and extractions.
  • the animal is nervous or uncooperative and is required to be very still for procedures such as X-rays, MRI or CT scans.
  • occasionally for ear cleaning (especially if the ears are very badly infected).
  • to control repetitive, uncontrollable seizures or heavy breathing leading to collapse of the windpipe.

Computed Tomography (CT) Scan is very useful for screening parts of the body such as the lungs, nasal passage, ear, abdomen & some orthopaedic structures. At the gantry, an X-ray tube rotates 360° around the patient to record X-rays from many angles. The animal has to remain very still for this procedure, hence the need for general anaesthesia.

what are the risks of anaesthesia?
  • Long Term Damage To Organs
    Anaesthetic drugs are processed by the liver and kidney. Anaesthesia also causes a drop in blood pressure which can lead to damage of the kidneys and other organs such as the brain.
  • Death
    No anaesthetic drug is completely risk-free. There is always a chance, however small, that an animal may not wake up from anaesthesia .
what are the key factors that affect anaesthesia risk?

1. Age
The older the animal, the greater the anaesthetic risk because there may be pre-existing conditions of the heart, lung, liver or kidney. Animals below 1 year of age have a slightly higher anaesthesia risk as their organs may not be fully developed yet.

2. Health Status
The healthier the animal, the lower the anaesthetic risk. Animals with pre-existing health problems (such as heart conditions) face greater anaesthetic risk .

3. Breed
Brachycephalic (flat-faced) breeds  such as the Pug, Bulldog, Pekingese and to a lesser extent, the Shih Tzu and Boston Terrier, have structural problems with the nasopharynx which make breathing more difficult when they are asleep and completely relaxed.

Induction & recovery phase (when the dog is going into & waking up from the anaesthetic) is particularly risky for flat-faced breeds like the Pekingese & Bulldogs. They may not get enough oxygen if their airways are not functioning well during that period.

4. Nature Of Procedure
Invasive procedures (open surgery) carry a higher risk than non-invasive procedures (e.g. dental cleaning).

5. Length Of Procedure
The longer the procedure, the higher the risk.

What can be done to minimise the risk?

1. Pre-anaesthetic Exam And Blood Tests
A thorough history of current and past medical conditions can provide valuable information about your pet’s health. Physical exam may reveal abnormalities of the heart or lungs which may require further evaluation such as an electrocardiogram, chest X-rays or ultrasound prior to surgery.

Pre-anaesthetic blood tests are important to check blood glucose, kidney and liver function and screen for pre-existing health issues, especially in older pets. Blood tests include:

  • Complete Blood Count
    To ensure there is no ongoing infection and to check the level of red blood cells and platelets, which are important in blood clotting.
  • Kidney & Liver Function Tests
    The kidney and liver are organs which process the anaesthetic drugs, so it is important they are working properly.
  • Heartworm & Tick Fever Tests
    Heartworm, which may not be detected on physical examination in early stages, can affect the heart’s ability to withstand stress, especially during surgery. Tick fever can affect blood clotting, which will greatly increase the amount of blood loss during surgery.

Your vet may suggest other blood tests based on your pet’s individual needs.

2. Intravenous Fluids
For older animals with a higher anaesthesia risk or undergoing longer procedures, your vet may include the usage of an intravenous (IV) drip. This helps your pet maintain hydration and blood pressure, process anaesthetic drugs faster and provides a convenient route for vets to administer fluids and other medication into the bloodstream during the procedure.

After an IV catheter is placed into a vein, the IV line is connected to an infusion pump to ensure an accurate amount of fluid is administered. This helps to keep your pet hydrated & maintain blood pressure. DrEstella Liew & Song of Mount Pleasant Central Vet Clinic (Whitley).

3. Airway Intubation
A soft plastic tube (endotracheal or ET tube) is inserted into the windpipe to maintain the airway for breathing. This is connected to an anaesthesia machine that delivers an inhalant anaesthetic in oxygen. It allows our vet to assist or control breathing if it becomes necessary. 

The ET tube also prevents inhalation of stomach contents into the airways, risking aspiration pneumonia. Read about Tiger’s maggot wound reconstruction surgery here.

* Fasting your pet for several hours prior to anaesthesia (as directed by your vet) is important. If your pet is not properly fasted, she could vomit during or shortly after being anaesthetised and possibly aspirate food or fluid into her lungs. Aspiration pneumonia can be life-threatening.

4. Anaesthetic Monitoring
The number one cause of anaesthetic complications leading to death is cellular hypoxia – cells are starved of oxygen. The patient’s vital signs such as heart rate, respiratory rate, blood pressure, blood oxygenation are continuously monitored throughout the anaesthetic procedure. Patients often experience hypothermia (reduced body temperature) during anaesthesia. Warming pads are routinely used to keep the patient warm.


In addition to a monitoring machine, a trained vet technician will monitor the patient’s heart rate, respiratory rate & anaesthetic depth during the procedure.


Patients often experience hypothermia (reduced body temperature) during anaesthesia. Body temperature may be further reduced with the use of intravenous fluids, clipping of fur and surgical preparation. Warming pads are routinely used during anaesthesia to keep our patients warm. Anaesthetic monitoring constantly measures the body temperature during surgery.

Warming pads and blankets are also provided after surgery to ensure our patients stay warm.

Pain management – rest better and recover faster

Pain management is crucial as it alleviates discomfort and helps our animals recover faster. Pain relief medication is usually administered before, during and after surgery. This helps reduce stress and pain associated with surgery, allowing the animal to rest better and recovery faster. It is always better to start on pre-emptive analgesia than to control pain once it has started. Read more about Managing Pain In Our Pets.

With appropriate pre-anaesthesia examination, careful monitoring and competent after-care, the risks of anaesthesia can be minimised. Most animals are back to their normal selves within 12 to 24 hours. If your pet does not fully recover from the anaesthetic by the following day, contact your vet immediately.

Dr Sarah Wong, Mount Pleasant Animal Clinic (East)
Dr Kasey Tan, Mount Pleasant Animal Clinic (North)