Veterinary anaesthesia: what you should know before your dog or cat has surgery

Being told your dog or cat needs general anaesthesia often causes more anxiety than the surgery itself. That’s an understandable reaction: it’s a procedure that involves losing consciousness and depending completely on the veterinary team, and it’s normal to want reassurance that everything will go well.

The reality is more reassuring than fear tends to suggest. Modern veterinary anaesthesia relies on individualised protocols, continuous monitoring of vital signs, and a pre-surgical assessment specifically designed to catch risks before they become problems. The data backs this up: the actual risk is low, and it has improved dramatically over the past few decades.

In this guide we explain what the research really shows about anaesthetic safety, what the pre-anaesthetic assessment involves, how your pet is monitored while under anaesthesia, and what questions you can ask your vet if you’d like to settle your doubts before the day of surgery.

Is anaesthesia dangerous for dogs and cats? What the data actually shows

The figure that tends to reassure owners the most is this one: according to the largest studies carried out in Spain, anaesthesia-related mortality currently sits at around 0.55% in dogs and 0.61% in cats. In other words, the vast majority of anaesthetised animals experience no serious complication linked to the procedure.

And that figure comes from a clearly positive trend:

The improvement over roughly two decades has been enormous, and it hasn’t happened by chance: it’s the result of anaesthetic protocols better tailored to each patient, more precise monitoring equipment and, above all, the fact that pre-surgical assessment has become a systematic step rather than a formality.

The pre-anaesthetic assessment: the key piece of the safety puzzle

If there’s one factor that explains the improvement in anaesthetic safety over recent years, it’s the pre-anaesthetic assessment. It isn’t a bureaucratic formality or a step designed only to decide whether an animal “can go into surgery” — its real purpose is to identify each patient’s individual risks and tailor the anaesthetic plan to them, before those risks turn into a problem during surgery.

This assessment typically includes:

• A full clinical history: previous illnesses, current medication, any past reactions to drugs.
• A thorough physical exam: heart and lung auscultation, assessment of mucous membranes, hydration, temperature and general condition.
• Additional tests depending on the case: a basic blood test is common even in animals that appear healthy, and in higher-risk patients it can be extended with X-rays, ultrasound or specific heart tests.

With this information, the veterinary team classifies the patient’s anaesthetic risk using the ASA system (from the American Society of Anesthesiologists), a five-level scale also used in human medicine. This isn’t just a label — it determines what level of monitoring is needed, what extra precautions to take, and what complications to anticipate before they appear.

How your pet is monitored during surgery

Once an animal is under anaesthesia, safety doesn’t depend only on the drugs used, but on continuous monitoring of vital signs throughout the entire procedure:

It’s common for one member of the team to be dedicated exclusively to this monitoring during surgery, without taking part in the procedure itself. That dedicated attention makes it possible to catch any change in vital signs immediately and act before it becomes a real complication, rather than discovering it after the fact.

Fasting before anaesthesia is also part of this safety picture: an animal with food in its stomach is at greater risk of vomiting or aspirating stomach contents during the procedure. That said, “fasting” doesn’t mean the same thing for every patient: current anaesthesia guidelines no longer recommend long fasting periods, and in puppies, kittens or very small animals, excessive fasting can actually be counterproductive due to the risk of hypoglycaemia. What matters isn’t fasting for “many hours” — it’s following the exact fasting window your clinic gives you, which varies by age, species and the individual animal.

Why risk changes with age and each animal’s health

Not every patient starts from the same point. Age and overall health directly affect anaesthetic risk, which is why the pre-surgical assessment isn’t equally thorough in every case.

In geriatric patients, anaesthetic risk is somewhat higher, even when the animal seems to be in good general condition. The reason isn’t age by itself, but the fact that past a certain age there’s a greater chance of systemic disease that doesn’t always show visible symptoms: heart, liver or, very notably, kidney problems. That’s why the pre-anaesthetic assessment in these animals often includes specific kidney and heart tests, precisely to rule out what can’t be seen at a glance. If your cat is getting on in years, you might find our guide on chronic kidney disease in cats useful — one of the conditions that most often shapes the anaesthetic plan in older feline patients.

In cats specifically, there’s another relevant heart consideration: hypertrophic cardiomyopathy, a heart muscle condition that’s relatively common in the species and, in many cases, doesn’t cause obvious symptoms until quite late. Ruling it out — or at least assessing the risk it poses — before anaesthesia is one of the reasons a specific cardiac exam is recommended in at-risk cats before surgery. We covered this test in more detail in our article on veterinary ultrasound and X-ray, where echocardiography appears as one of the main indications for the technique.

In young, healthy animals, on the other hand, baseline risk is low, though the pre-surgical assessment is still carried out just the same: the absence of symptoms doesn’t rule out checking that everything’s in order before anaesthetising. It’s exactly the same principle we apply, for example, in routine procedures like spaying and neutering dogs and cats, where a pre-surgical assessment is also carried out even in young, apparently healthy patients.

Pain control is also about safety, not just comfort

It’s easy to think of pain relief as something aimed purely at an animal’s comfort during recovery, but its role in anaesthetic safety is just as important. Poorly controlled pain during or after surgery triggers a stress response in the body — the release of stress hormones, increased heart rate and blood pressure — that can complicate both the procedure itself and the recovery that follows.

That’s why pain management is planned alongside the rest of the anaesthetic protocol, not added afterwards as an extra: it’s tailored to the type of surgery, the species and each patient’s individual characteristics, just like the rest of the anaesthetic plan. An animal with well-controlled pain isn’t just more comfortable — from a purely physiological standpoint, they’re more stable too.

What you can ask your vet before surgery

If your pet has surgery scheduled and you’d like to settle your doubts calmly, you’re entitled to request a pre-anaesthetic consultation ahead of the day of the procedure. Some questions that can help put your mind at ease:

• What tests will be run before anaesthesia, and why, in your pet’s specific case?
• Is there anything in their history — age, breed, existing conditions — that changes the standard anaesthetic plan?
• How will they be monitored during surgery?
• What fasting instructions should I follow before the day of the procedure?
• How will pain be managed during and after surgery?
• What signs should I watch for at home during recovery?

None of these questions are excessive or out of place. A veterinary team that takes anaesthetic safety seriously will answer them readily, because they’re part of the very same process already being applied to your pet’s assessment.

Frequently asked questions

Could my pet die from anaesthesia?

The risk exists, as with any procedure under general anaesthesia, but it’s very low and has dropped a lot over the years thanks to better protocols, monitoring and pre-surgical assessment. The aggregate data is reassuring, though it can’t promise a specific outcome for any individual animal — that’s why an individual assessment is carried out before every surgery, tailored to your pet’s own health.

Is anaesthesia riskier in cats than in dogs?

Cats have, overall, a slightly higher anaesthetic risk than dogs, partly because they metabolise certain drugs differently and tolerate hypothermia during surgery less well. Even so, the difference is small and is offset by monitoring and an anaesthetic plan tailored to the species.

What happens if my pet is older?

In geriatric patients, anaesthetic risk is somewhat higher — not so much because of age itself, but because there’s a greater chance of underlying systemic disease (heart, kidney, liver) that isn’t always obvious from the outside. That’s why the pre-anaesthetic assessment matters even more the older the animal is, and it usually includes extra tests to rule out these problems before scheduling surgery.

Why do they ask for blood tests before surgery if my pet looks healthy?

Because an animal’s outward appearance doesn’t guarantee that internal organs — liver, kidneys — are working normally. A blood test beforehand can pick up silent changes that might affect how anaesthetic drugs are metabolised, so the protocol can be adjusted accordingly. It’s a safety measure, not a generic formality.

If your dog or cat has surgery coming up and you’d like to settle your doubts before the day of the procedure, at Rovira Veterinary Clinic we carry out an individualised pre-anaesthetic assessment for every patient, with monitoring and an anaesthetic plan tailored to their specific case. Check out our surgery services or get in touch with us to have your questions answered and book an assessment.