Anesthesia, effects on cognitive functions

Surgical anesthesia is intended to render the patient insensitive to pain. In a typical clinical procedure, known as balanced anesthesia, the patient is premedicated with a sedative intended to relieve preoperative anxiety and facilitate the induction of anesthesia itself. Often this premedication is a benzodiazepine such as diazepam or midazolam; otherwise, a barbiturate such as thiopental or a nonbenzodiazepine such as propofol may perform this function. Sedation is followed by the induction of general anesthesia by intravenous injection of a sedative, narcotic (e.g., morphine, fentanyl, or alfentanyl), or ketamine. In addition, a nondepolarizing curare-like derivative (e.g., vecuronium or d-tubocurarine or a depolarizing drug (e.g., succinylcholine) is administered to induce muscle paralysis. After intubation and connection to a ventilator for artificial respiration, general anesthesia may be maintained by a mixture of oxygen and nitrous oxide, often in combination with a volatile agent (e.g., halothane, enflurane, or isoflurane) or an intravenous narcotic. At the conclusion of the surgery, muscle relaxation is reversed (e.g., by neostigmine or other anticholinesterase), and normal (unassisted) breathing is restored. In addition, the patient may be given an analgesic agent (e.g., morphine) to manage any acute pain experienced postoperatively.