A survey published in 1996 reported that there were 107 countries where nurses administer anesthesia in some form, and a further nine countries where nurses act as assistants in the administration of anesthesia. Depending on the local system of healthcare, they may participate only during the operation itself, or may also be involved before and after (for preanesthetic assessment and immediate postoperative management). In some systems nurse anesthetists must provide anesthesia under the supervision of anesthesiologists, while elsewhere they provide anesthesia independently.