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Is My Pet Too Old for Anesthesia?

2018-04-23

As a veterinarian, I am often faced with this question when discussing procedures that involve sedation and/or anesthesia.  There has been a long-held notion – and a lot of misinformation around the internet, etc. – that age is an anesthesia risk.  It’s not entirely a surprise – after all, we visualize in our minds a young, presumably healthy person compared to an aged, decrepit individual with numerous health problems.  Of course we would feel confident that the young person would be just fine while we would imagine the old-timer unlikely to survive the procedure.

To set the record straight: Age is not an anesthesia risk!

To assume that age is an anesthesia risk results in two big mistakes that I encounter pet owners – and unfortunately some veterinary practices and shelters – making on a regular basis:

  1. Failing to address a medical problem that is treatable or curable when an “older” patient is healthy enough to do well under sedation or anesthesia.  This can result in unnecessary suffering on the part of the pet and/or allow a problem to continue to worsen over time.
  2. Assuming that a “young” patient is perfectly healthy and failing to do a proper pre-anesthesia evaluation.  This can result in missed medical risks and result in avoidable sedation or anesthesia complications.

So if age is not an anesthesia risk for my pet, then what is?

Factors that can increase a pet’s risk under sedation or anesthesia include certain heart disease(s), lung disease(s), metabolic disease(s), kidney disease(s) and liver disease(s).  To be fair, these kinds of diseases can be more common in older patients, but they are not exclusive to old age – young patients can be affected as well. 

  • The Lungs are responsible for transferring oxygen from the air and eliminating waste (e.g. CO2).  They are also responsible for the transfer and balance of anesthesia gases (e.g. Isoflurane, Sevoflurane).
  • The Heart is responsible for bringing oxygen and nutrients to the body through the blood, moving drugs around the body and maintaining blood pressure.
  • The Kidneys and Liver are actively involved with removing drugs from the body, so when these are not working properly, a patient may accumulate too much drug in the body and be at risk of overdose and/or unwanted side effects.
  • Certain metabolic diseases may have effects on healing, ability to maintain blood pressure, ability to handle the stress of a procedure, ability to maintain body temperature and more.

The American Society of Anesthesiologists (ASA) established statuses that can be attributed to varying levels of anesthesia risk, and these statuses have been statistically shown to be applicable to pets as well.

Ideally, your pet will fall into the ASA level I or II categories.  ASA level I pets are perfectly healthy, and their risk of a complication under anesthesia should be around the order of 1 in 10,000 – pretty good odds of being just fine!  ASA level II pets may have a disease that is mild or well managed, such as a heart murmur in an otherwise stable heart or diabetes that is well-regulated on insulin therapy. 

ASA level III gets a little more tricky – these pets have a medical problem that is more severe and/or unregulated.  These pets can have a higher risk of anesthesia complication(s) due to their disease(s).  Depending on the disease(s) and the risk(s) of delaying the recommended anesthesia procedure, your veterinarian may 1) alter the anesthesia plan to try to mitigate these risks or 2) recommend delaying the procedure to address the disease(s), with the goal of getting the pet to a more mild – and less risky - ASA level II status. 

ASA level IV and V pets are at high risk for complication(s) under anesthesia, but these patients are usually only going under anesthesia due to an emergency situation.  An example would be a dog who was in a car accident and an injured spleen is actively bleeding into its abdomen – a high anesthesia risk, but the veterinarian needs to perform immediate surgery to stop the bleeding. 

Before any anesthesia procedure, your veterinarian should be evaluating your pet to determine their overall health, ASA status and anesthesia risk.  This should involve a physical exam, some bloodwork and possibly – if recommended – other laboratory testing or imaging.  They should also be consulting you about your pet’s individual risk(s) and whether the risk:benefit of a given procedure is in your pet’s best interest.  As a veterinarian, I have encountered very old – and healthy – patients that did very well under anesthesia.  I have also seen young puppies with previously undetected disease that made them a high anesthesia risk.  We also commonly see pets with mild and/or managed disease(s) that do great under anesthesia and benefit immensely from their recommended procedure.

Before assuming your pet is too old or too ill to undergo a recommended procedure - or that they are young and invincible - make sure you talk with your veterinarian about what your pet’s true risk(s) may be.

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