How long can you be under anesthesia?

There is no evidence that the duration of general anesthesia by itself increases the risks of anesthesia complications. Studies of anesthesia-related risk have shown correlation with other factors, such as:

1. Your general medical condition especially problems like Diabetes, heart or lung disease, malnutrition or obesity,
2. Your functional status, that is your ability to tolerate at least moderate levels of physical activity.

Obviously, anesthetic outcomes are also related to the skill and experience of the anesthesiologist that is taking care of you. The anesthetic needs to be tailored to your medical condition, to the surgery itself, and wherever possible, to your individual preferences.

Source: http://lifelinetomodernmedicine.com/faqs.aspx