[PennysMum]

There are many conditions that will not show up on a standard pre-surgical blood screen. A dog could look okay on a Chem 6 and still have a heart condition, or even a liver shunt.

Human error factors in a lot of the time when there are complications in surgery. When an animal is under anesthesia, it should be constantly monitored to make sure that it is well oxygenated and to make sure that its blood pressure is within an acceptable range. For example, gas anesthesia causes dilation of the animal's blood vessels, meaning that blood pressure can drop quickly if the pet is on too high of a level of gas. This usually isn't an issue since someone should be standing by and taking readings of vital signs during the procedure and adjusting the level of gas as needed. But... if they aren't monitoring closely enough, things can get hairy pretty quickly.