The first was about 14 years ago while practicing in Arizona. The clinic had a young white purebred puppy come in to be neutered. He was anesthetized and his surgery seemed to go fine. He was sent home that afternoon still a little groggy. The owners called the next day and he was not feeling well and was vomiting. They were told it was likely the anesthesia making him naseous and to keep an eye on him. The next day was no better, and he returned to the clinic. He was treated with fluids to help rehydrate him, and sent home. Finally a few days later he seemed to be feeling better. One month down the road he ate something he shouldn't have, and vomiting had to be induced. At the time, salt was recommended, and he vomited up the offending candy. For the next several days he vomited off and on and felt terrible. Finally he seemed to turn the corner and improve. Two weeks later the owners brought him back to the clinic because he was laying around all the time and drinking and peeing a lot. Bloodwork was done then, and that 7 month old puppy was in kidney failure!! He lived about one more month and then had to be euthanized.
The second case was just a couple months ago. A young female mixed breed dog came in to be spayed. We did some pre-anesthetic labwork and found very elevated liver enzymes. This little dog's liver was working too hard and had something wrong with it. Instead of going ahead with the spay, we performed some additional bloodwork that we sent into the lab. She went home just as happy and perky as when she came in, and all we did that day was draw blood.
The biggest difference between these two cases was the labwork that was or was not done before the surgery. In the first case, we went ahead with anesthesia which compromised the already ailing kidneys and in all liklihood hastened the progression of his kidney failure. The second case has yet to play out to the end, but by knowing what was going on inside, we avoided doing any harm to the puppy. Pre-anesthetic labwork is an amazing and valuable tool to the pet, the owner, and the veterinarian. That is why we recommend it with any surgery.