As some of you may have read, at the end of September last year, Marwell Zoo, unfortunately, lost one of their much-loved residents; the beautiful 11year old female Amur Tiger, “Milla”. She was undergoing a planned anaesthetic for routine health checks, vaccination and to have a contraceptive implant placed; however, her heart stopped beating and she sadly passed away.

All staff involved were of course devastated, and this undoubtedly will sit heavily in their hearts for years to come. For the veterinary profession, the unexpected loss of a seemingly healthy animal under anaesthesia is truly distressing. The after-effects can be psychologically profound; Milla’s death will have left the medical team with an enormous burden of guilt and regret. 

But how common are such complications and do you need to be concerned when the vet has recommended that your pet, a domestic cat, should undergo an anaesthetic?

The stats

Fortunately, the risks with a health animal undergoing an anaesthetic are small. Whilst any anaesthetic death is undesirable, the actual probability of a problem and the incidence rate of complications, are both relatively low. Put into figures, studies have shown for healthy animals there is a death rate of approximately 0.12%. That translates to roughly 1 animal in every 1,000. 

Unfortunately, but perhaps unsurprisingly, unwell or sick pets, will have greater risks. There are also other underlying conditions that will increase the risks – either intra-operatively (at the time of the anaesthetic / procedure – such as heart failure), or, post-operatively (after the anaesthetic / procedure – such as kidney disease). 

What about old age?

Age is however, not a disease in its own right, but there are considerations that need to be borne in mind for older patients. Elderly cats will have altered, often reduced physiology and metabolism and may not be able to compensate for the effects of anaesthesia as well as a younger patient. Co-morbidities (other co-existing diseases) may also frequently interfere with the anaesthetic. 

Anaesthesia will need to be sympathetic to each cat, particularly these older patients, to provide a stable and positive experience for both the cat and the veterinary team.

Emergencies are more complex

It may however, in emergency situations, be difficult to balance pre-operative stabilisation against the need for rapid surgical intervention. This may be the case for example, in an animal with an actively bleeding intra-abdominal tumour. Severe injuries or illnesses would usually increase the anaesthetic risk.

Minimising risks

All vets are proactive in trying to minimise anaesthetic risks. Whilst we cannot eliminate every risk factor, the dangers can be very much reduced through careful patient selection, pre-operative assessment, and thorough monitoring under the anaesthetic.

History and physical examination

Anaesthetic planning starts by taking a complete medical and surgical history of your cat, alongside performing a careful and detailed pre-operative examination. Within the history, the age, breed and sex of your pet, along with their body weight and body condition score (BCS) are key factors in determining which anaesthetic drugs may or may not be suitable. All drugs administered will be “titrated” (dosed) according to (lean) body weight. The next steps include;

  1. You may be questioned on previous episodes of collapse, presence of any “faints or fits” and asked whether you have any reason for concern. 
  2. Any medications that your cat is taking should be discussed along with a conversation about when the last doses were given. 
  3. You must ensure that your Vet has an up to date telephone number for you and upon which you can be contactable in the event that this is needed. 
  4. You will be asked to complete a consent form that explains the procedure your cat is undergoing. The consent form should also document the associated risks or possible complications.
  5. Your vet will listen to your cat’s heart, check the colour of their mucous membranes, assess their breathing rate and effort, and take a temperature. All to ensure that these parameters fall into the expected normal ranges, and also to serve as a baseline for subsequent anaesthetic monitoring.
  6. “Pre-oxygenation” (placing the cat in a pure oxygen environment), will occur if there are cardiac or respiratory concerns. An intravenous catheter will be placed to allow for administration of drugs, should that become necessary. 

Bloods and fluids

Pre-operative blood tests may have been discussed, advised or be an optional “extra”. As a vet it is impossible to say that these are ever a bad idea, given they are there to pick up the rare, but not infrequent cases of say, early subclinical renal disease for example. These pre-GA blood tests, whilst not being fully comprehensive, do give pertinent information about the underlying health status of your cat in terms of liver and kidney function, blood sugar and protein levels and red blood cell numbers. They should, ideally, be performed in the majority of cases. 

Intravenous fluids may also be an option you can select for your cat. Again, it is hard to say these are ever contraindicated; cats with heart failure or advanced heart disease might represent an exception. Fluids will help support blood pressure under anaesthesia, which in turn supports liver and kidney blood supply. Given these organs are responsible for metabolising and eliminating the anaesthetic, patients receiving them, should endure both smoother anaesthetics, with swifter recoveries. 

The patient assessment

Additionally, to help assess our patients, the ASA (American Society of Anaesthesiology) has developed a scaling system which helps evaluate whether any individual patient is healthy and able to withstand anaesthesia. The ASA scaling system marks animals on a scale of 1-5 according to their health status and carries an additional “E” (emergency) category, to be used when necessary. This helps focus our attention on the cases where we may expect problems, by understanding how the health of the patient may affect anaesthesia.  

How is my cat monitored under the anaesthesia?

As a minimum under anaesthesia the veterinary nursing team will monitor eye position, the blink reflex and jaw tone (which help dictate whether the depth of anaesthesia is appropriate). Heart rate, breathing rate and temperature are also monitored. Typically, these parameters are assessed continually and recorded every 5minutes. In doing so, any trends or concerns are quickly recognised and treated.

There are many advanced monitoring tools these days and in my practice, we always use these in anaesthetised patients. Pulse oximetry measures the oxygen delivery to tissues, ensuring this remains adequate. Blood pressure monitoring ensures adequate blood perfusion to vital organs in the body. Capnography assesses the amount of expired carbon dioxide in a patient’s breath and thus the adequacy of respiration. An ECG looks at the heart conduction and rhythm. 

Your cat will be kept as warm as possible with various heating devices, since hypothermia affects anaesthesia and can also increase the risk of complications.

So what could go wrong… at the time of anaesthesia?

Complications that may arise under the anaesthetic, include breathing concerns such as “breath holding”, and heart rhythm or heart rate abnormalities. Low blood pressure and hypothermia (low body temperature) should be addressed if recognised to occur. 

And what could happen… after the anaesthetic?

The “recovery” phase of anaesthesia is often deemed the most risky, so close continued observation from the veterinary team during this time is of paramount importance. Potential concerns include aspiration pneumonia (inhaling vomited stomach contents), regurgitation, respiratory obstruction, blindness or corneal ulcers (cats eyes stay open during anaesthesia, so we have to apply protective drops – this usually works, but complications occasionally happen).

How can I take steps to help?

Obesity is an enormous risk factor for anaesthesia, compromising the patient’s ability to breathe considerably. Keep your cat at a good weight and body condition score to avoid undue risks. Observe your cat for any subtle changes in behaviour, appetite and thirst, which may give your vet clues to any underlying diseases.

Consent to pre-anaesthetic blood tests for your cat, especially if middle-aged or old or with concerning symptoms. Opt also, for intravenous fluids during the anaesthetic.

Whilst anaesthesia (like any medical procedure) carries some risk, with thorough and careful pre and intra op consideration and monitoring, the risks can be minimised. Hopefully, the benefits of undertaking the advised procedure, will always vastly outweigh the small anaesthetic risk involved.

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