He wanted to lighten Nancy's level of anesthesia.

Several factors are taken into consideration when determining which level of anesthesia is used under which type of medical procedures.

The dermatomal level of anesthesia required for Caesarean delivery is also higher than that required for labor analgesia.

In studies of 270 patients, Dr. Eger found that only a handful who had unusually low levels of anesthesia remembered anything about their surgery.

This makes a deeper level of anesthesia achievable more easily using anesthetic gases but can also make them more dangerous than other drugs used for this purpose.

Repetitive (small) doses of local anesthetic to achieve an adequate level of anesthesia may lead to eventual administration of toxic doses.

Two years ago the American College of Surgeons and the American Medical Association urged states to develop guidelines for office-based surgery according to the level of anesthesia used, among a host of other things.

It was further found that after thiopental induction, it was necessary to administer nitrous oxide for at least ten minutes before a sufficient amount of methoxyflurane could accumulate in the bloodstream to ensure an adequate level of anesthesia.

In such cases, the patient may be anesthetized to a lower BIS level than is necessary for the surgery or procedure-this is called "treating the BIS," and may result in a deeper level of anesthesia than required).

"I don't believe patients can register and respond to what is said during surgery at deeper levels of anesthesia," said Dr. Edmond Eger, professor of anesthesia and vice chairman of anesthesia research at the University of California at San Francisco.