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Friday, February 27, 2009

Preanesthetic Blood Testing

Remember yesterday's post? Well, we did get the disc and the analyzer worked well today. Surgeries were able to proceed normally, and we got through the day without any further technical difficulties. But the whole thing made me think of another topic of discussion.

Many people might say "well, you're dealing mostly with young, healthy pets. Would it really have been that big of a deal to do the surgery without the blood tests? Isn't it really unnecessary? After all, vets used to do surgeries without anything like this." All of these are great questions. To answer them in short...yes, it would have been a big deal, yes it's necessary, and yes vets used to do without it but also had a higher complication rate.

When we do an exam on a pet, we can only evaluate certain things. One of the things we cannot evaluate is the function of the various internal organs. We can't just look at a pet and tell if the kidneys or liver are working properly. These are very important when it comes to anesthesia, as the body eliminates the drugs through these two organs. If they're not doing their job, then the drugs may not be eliminated properly, leading to prolonged anesthesia or other complications. To give you an idea of how misleading an exam might be, you have to loose 66% of your kidney function before you will have any abnormalities in lab tests, but have to loose 75% of the function before you act sick. So there is a window between 2/3 and 3/4 kidney failure where you look, act, and feel perfectly fine, but there are detectable abnormalities.

Well, what about the fact that many patients are young? Doesn't that lower the risk? Yes, it does. The older a pet is, the more likely we are to see organ dysfunction. However, there are numerous abnormalities that we are more likely to see in young pets, such as kidney cysts or a liver shunt (where blood flows around the liver rather than through it). No, we don't see these things often. But I have diagnosed many young, apparently healthy pets with various diseases that we detected in a pre-anesthetic blood panel. Older pets are even more likely to have problems detected. If we did anesthesia without knowing for certain, we would potentially be placing the pet at risk for complications.

It all comes down to knowing or guessing. Do you want your doctor to make a guess about whether or not your pet's organs are normal, or do you want him/her to know for certain? If the preanesthetic testing isn't done, then you are doing nothing more than making a guess, and in a way gambling as surely as rolling dice in a game of craps. Personally, I don't like guessing when I have other alternatives.


  1. Thank you for expressing it so well. We also do yearly bloodwork on our pack to see if there have been any changes.

  2. That's another great point. Regular blood testing is very important to catch chronic or developing problems early.

  3. What drugs do you use to maintain anaesthesia? Newer volatile agents do not undergo significant biotransformation and are excreted from the body via the lungs hence recovery is unlikely to be prolonged in cases of organ dysfunction. Propofol undergoes significant extra-hepatic metabolism.

  4. Both comments are correct. However, there can be other concerns. We do use propofol, but even though it undergoes extrahepatic metabolism, there is some metabolized by the liver. It is also lipid-bound, so if the serum is lipemic you can have prolonged anesthesia; and you won't know this without pre-anesthetic blood sampling. We do use acepromazine as a standard pre-anesthetic sedative, which is more significantly metabolized by the liver. Also, the liver produces significant clotting factors. If the liver isn't functioning normally, clotting can be affected. Not something you want when you're doing surgery!


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