Wow...any other physical signs...reddness or bloating of the face? Have they checked for infection..i'm sure they have if they are doing routine blood work..if its an allergy to the anethesia drugs they should know that right away.......
While this is very rare, there are several problems that could prevent a patient from waking up after a general anesthetic. Many of these are not directly related to the anesthesia itself. A comatose patient could have a serious metabolic problem, such as an electrolyte disorder, liver or kidney failure. Respiratory (lung) failure is another potential cause. A lack of oxygen to the body can cause permanent brain injury and coma. There may be a problem with inadequate blood flow to the brain, a blood clot or bleeding into the brain (stroke). In a few patients, for a variety of reasons, there may be slowed elimination of drugs from the body, and therefore delayed recovery from anesthesia. In time these patients will usually wake up fully, unlike the person who has had a permanent injury to the brain.
Please don't let this scare you...just make sure someone is covering all the bases with the doctors. Your sister definately needs an advocate right now to ask all the hard questions. So sorry........Pat