Anesthetic depth is on a spectrum, and practitioners will mean different things while using the same terms. In general, twilight anesthesia means that the patient is just on the verge of being asleep and can still respond and protect their own airway - they are just at the precipice of slipping into general anesthesia. Once you enter the realm of general anesthesia, the patient cannot protect their own airway, so some type of breathing tube is used to keep it open (such as a Laryngeal Mask Airway or an Endotrachial Tube). General anesthesia is quite safe, as your airway is fully protected. Twilight is a bit of a balancing act, but can be done quite well by vigilant anesthesiologists. My concern with twilight anesthesia is that it does not necessarily require an MD anesthesiologist to be present - it could be managed by the operating surgeon and monitored by an RN. Some surgeons will go this route as a cost savings measure (MDs are more expensive than RNs), but I do not think this is a good place to cut corners. If your surgeon uses an anesthesiologist and they prefer twilight, then it should be fine. I would not recommend twilight if it is going to be managed by the operating surgeon. (Think about it - are you better at concentrating on one task, or trying to do two things at the same time?)
M. A. Bogdan, MD