PreAnesthesia Laboratory Testing

One month from today is Peyton’s birthday. He would have been 15 years old that day, but he passed away about three years ago. He was much-loved.

Peyton had the most soulful eyes, his eyes could talk.
Peyton had the most soulful eyes, his eyes could talk.

For two years and nine months Peyton was the “poster child” for pre-operative laboratory testing at our practice. He continues to be, even after his passing.

It all started in May of 2003, when our two dogs, Peyton and Pearl, needed to have their teeth cleaned. Before anesthetizing them, though, I wanted to be sure that they were truly healthy enough for general anesthesia. Oh, they looked well enough, played hard, acted happy and had a good appetite. But looks can be deceiving.

As Peyton proved.

The shock was all over my crestfallen face when I got the laboratory test results back for Peyton and it showed he had serious liver enzyme elevations. Over the next two months I ran additional tests and proceeded with symptomatic therapy, but the numbers kept coming back abnormal.

Peyton appeared solid and healthy, but his preanesthesia laboratory tests showed he was not.
Peyton appeared solid and healthy, but his preanesthesia laboratory tests showed he was not.

I called a friend who is a board-certified veterinary internist and scheduled an ultrasound of his abdomen. When he told me that Peyton might make it two more years you could have mopped me up from the floor. He was only nine and I had fully expected to have him another nine years. The sad news was that already two-thirds of his liver was gone. He would require a liver biopsy to determine what the status of the rest of his liver was.

Keep in mind that this little twelve pound bundle of energy never missed a lick (or a meal), yet he was already dying.

Had we not performed those tests, and had proceeded with anesthesia, we would likely have lost him over three years sooner. Today, then, we will look at the most basic highlights of why your pet’s doctor asks you to perform certain tests prior to surgery or other procedures requiring anesthesia.

General anesthesia requires a cooperative effort of quite a number of organ systems in order for the patient to become anesthetized, undergo a procedure, then wake up healthy. While all of those organ systems don’t have to be perfect, they do have to function at least to a certain minimum. And, if there is a functional problem, the anesthesiologist needs to know before a crisis occurs, not in the middle of the procedure.

Further, if some organs are not fully up to par, and the person administering anesthesia knows in advance, he can tailor the type and/or amount of anesthetic to account for the problem.

While it’s hard to say one organ is more important than another (which one do you want to be without?), most doctors would agree that from an anesthesia viewpoint, the liver and kidneys are tied for first place when it comes to pre-anesthesia testing. It’s also important that electrolytes (sodium, potassium, calcium, phosphorous and chloride, especially) be in a good balance with each other.

To find the status of these parameters, normal or abnormal, we perform a chemistry profile. Depending on your pet’s individual history and needs, as well as age and type of anesthesia anticipated, three to 25 chemical parameters may be tested. Each different chemical parameter gives your pet’s doctor a clue about your pet’s health, or illness.

Another routine part of pre-anesthesia testing is the CBC, or Complete Blood Count. The CBC will be evaluated to determine by up to six parameters whether your dog or cat has adequate red blood cells. Too few indicates that he is anemic. Anemias come in various types, and the quantity, size, shape and color of the red blood cells gives us the information we need to evaluate anemia. With too few red blood cells there may be inadequate transport of oxygen to vital organs during anesthesia.

Another important factor to evaluate in the CBC prior to surgery is the quantity and type of white blood cells (WBCs). There are four main types. Too few and healing may not progress at the proper pace. Too many, especially too many of one or two certain types, and the indication may be that there are problems that should preclude anesthesia until the source of the excess WBCs is revealed.

A tiny little unit that we need to evaluate before we leave the CBC is the platelet. Platelets are fragments from a big cell called the thrombocyte. Platelets are a crucial physical part of the complicated process of blood clotting. If the patient has too few platelets, an incision in surgery could cause him to bleed fatally. The cause of low platelet count would be determined prior to initiating surgery.

Peyton was a very loving little boy.
Peyton was a very loving little boy.

Thanks to those first preoperative screening tests, a lot of medicine, a lot of patience, and a ton of love, Peyton made it two years and nine months beyond what his internist had forecast. How incredibly grateful we are for each and every day we had.

Without those preanesthesia laboratory tests, however, he would likely have died during his dental cleaning. What a sad and unnecessary loss that would have been.

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