Anesthesia also comes with risk factors, and can be harmful depending on the surgery or patient's risk. "Awareness can occur when there is too light of anesthesia, which we often do deliberately for high-risk situations," says Cole. According to the American Society of Anesthesiologists, high-risk surgeries include heart surgery, brain surgery, and emergency surgeries in which the patient has lost a lot of blood or they can easily go into shock.
Or the patient may need a lower dose of anesthesia due to risk factors such as heart problems, obesity, a genetic factor, or being on narcotics or sedatives. "For instance, anesthesia depresses the heart, so a normal dose could be life-threatening to someone with heart problems," Cole explains.
"Sometimes you have to make a trade off," says Cole. "Would you rather have a high level of anesthesia which threatens your body's life functions, or a low level which ensures safety but increases the risks of waking up during the procedure?"