Please, please get the bloodwork done! It's especially important for Yorkies to have it done since the breed is prone to liver disease. Anesthesia is processed through the liver.
Do you know what type of anesthesia they are using? You have to be very careful with those low cost spay neuter clinics as toy breeds need a special protocol.
Have you read this?
http://www.yorkietalk.com/forums/yor...-protocol.html