Doctor Dinner, Anesthesiologist of New York Presbyterian Hospital Weill Cornell Medical Center, explains how unusual awareness is under general anesthesia, but explains methods for keeping track of patients should it occur.

Doctor Dinner: The question comes up frequently with patients, parents, children - what if I'm awake during my surgery and you don't know it as the anesthesiologist? More often than not awareness happens in extremely sick people who are brought to the operating room in a very fragile state and are given smaller concentrations or quantities of drugs because of the potentially toxic effects of these drugs. When a patient undergoes general anesthesia, there are a host of monitors that are in place, monitoring vital functions. The state of awareness is usually one that triggers autonomic responses, blood pressure goes up, pulse goes up, patients may tear, they may move. There are devices that are used to monitor awareness. We have a pretty good handle on how much we're giving and the anesthesiologist is pretty much on top of the situation. Not that awareness doesn't occur but it's extraordinarily unusual.