Laboratory testing preanesthesia or presurgical
Veterinarians are a cautious set of people. When given the opportunity to perform what some people consider a "routine procedure". Prudence and safety give one pause to wonder. Does that cat look and act as frisky on the inside as it appears on the outside? More importantly they do not like making phone calls to owners if major problems occur.
I have a new "poster child" for pre-operative laboratory testing in our practice.
I had an eight month old cat scheduled for an ovariohysterectomy (spay) yesterday 3/16/2009. This is a very alert friendly well mannered cat with a body condition score of 5.5 out of 9.0. A 5/9 is considered ideal muscle mass to frame ratio. No oddities picked up on pre-exam. There was not an outward clue of internal issues. During our presurgical screen it was detected that liver enzymes were markedly elevated. Most Of the Veterinary medicine gurus do not get suspicious or pay attention until a test result is twice the upper end of a normal range. There are exceptions. As an attention getter a feline ALT (liver enzyme) test is reported in the Idexx system as 649 U/L (12-130 normal range) and AST (liver enzyme) 245 U/L (0-48 normal range). Feline half life of ALT is about six hours. A test result of 649 is an easy math 5 times upper normal range. Had we not done those tests, and had proceeded with anesthesia, we would have lost her under anesthesia. I discussed options with owner and we elect to first try medications and if not improved to consider an ultrasound referral appointment.
It is better to check for problems to rule out any untoward effects of anesthesia. Kidney and liver are the main systems to convert the anesthesia needed to give an adequate plane of surgical anesthesia. We need functioning systems to detoxify the pre-medications and the inhalant gas used for a successful procedure.
This is a safety net or a very big flashing indicator if something is out of range. It is an indication to scratch any planned elective surgical procedure for that day. It is a huge opportunity to find out what is the problem and plan option B for anesthesia. Some times elevations may be a clue where to look for a more precise pin point diagnosis. A rational treatment plan may be outlined if it is a medical / drug curable option. Other test may be needed to rule out liver portal shunt, microvascular anomaly or detailed imaging procedures may be requested to establish exactly what is causing the problem.
James Irwin, DVM, did a preanesthesia study in his practice in Silver Springs Missouri. Dr Irwins in house study showed out of 1200 cases done in his practice study there was close to ten percent showing some form of abnormality in the test results. This means additional test or procedures are indicated for further diagnostics. The spectrum of problems found was minor problems, to major issues and all the way to "You have to be kidding". Some findings will alter anesthesia choices, choice of intravenous fluids or even discover a need to stop a procedure today.
In a previous article written in January of 2009 I wrote about a puppy named "Z" with renal (kidney) failure at 17 weeks of age. Putting Z under anesthesia would have been an outright disaster. She was not scheduled for any procedure but you understand the concept. You have heard of the saying "You can not judge a book by its cover" That axiom is true in veterinary medicine also. Looks can be deceiving.
Clients need to look at why a veterinarian asks you to perform certain tests prior to surgery or other procedures requiring anesthesia. It is a health safety issue.
Anesthesia requires a cooperative effort of a number of organ systems for a patient to be anesthetized, go through a procedure, and most importantly wake up healthy and not in a vegetative state or dead.
Tests are for the pets we want to wake up. It is that simple.
For more information about a specific case, consult your veterinarian.