In the practice of medicine, especially surgery, and dentistry, anesthesia (or anaesthesia) is an induced, temporary state with one or more of the following characteristics: analgesia (relief from or prevention of pain), paralysis (extreme muscle relaxation), amnesia (loss of memory), and unconsciousness. A patient under the effects of anesthetic drugs is referred to as being anesthetized.
Terminology varies between countries. In North America, the term anesthesia refers only to the act itself of administering anesthetics to a patient, while the medical speciality that focuses on this is referred to as anesthesiology and the physician who performs it is termed an anesthesiologist. By contrast, in the United Kingdom and other countries following the British tradition, anaesthesia denotes both the medical speciality and the treatment delivered, and the physician who performs it is termed an anaesthetist (in North America, the word anesthetist indicates a nurse anesthetist who delivers anesthesia under the supervision of a physician).
Anesthesia enables the painless performance of medical procedures that would cause severe or intolerable pain to an unanesthetized patient.
Three broad categories of anaesthesia exist:
General anesthesia suppresses central nervous system activity and results in unconsciousness and total lack of sensation.
Sedation (or dissociative anesthesia) inhibits transmission of nerve impulses between the cerebral cortex and limbic system, which inhibits both anxiety and creation of long-term memories.
Conduction anesthesia, commonly known as regional or local anesthesia, blocks transmission of nerve impulses between a targeted part of the body and the spinal cord, which causes loss of sensation in the targeted body part. A patient under conduction anesthesia remains fully conscious. Two categories of regional anesthesia exist. A peripheral blockade inhibits sensory perception in a body part, such as numbing a tooth for dental work or administering a nerve block to stop sensation from an entire limb. A central blockade administers the anesthetic around the spinal cord, which suppresses all sensation below the block. Examples of central blockade include epidural and spinal anaesthesia. In preparing for a medical procedure, an anesthesiologist chooses and determines the doses of one or more drugs to achieve the types and degree of anesthesia characteristics appropriate for the type of procedure and the particular patient. The types of drugs used include general anesthetics, hypnotics, sedatives, neuromuscular-blocking drugs, narcotic, and analgesics.
There are both major and minor risks of anesthesia. Examples of major risks include death, heart attack and pulmonary embolism whereas minor risks can include postoperative nausea and vomiting and hospital readmission. The likelihood of a complication occurring is proportional to the relative risk of a variety of factors related to the patient's health, the complexity of the surgery being performed and the type of anesthetic. Of these factors, the person's health prior to surgery (stratified by the ASA physical status classification system) has the greatest bearing on the probability of a complication occurring. Patients typically wake within minutes of an anesthetic being terminated and regain their senses within hours. One exception is a condition called long-term post-operative cognitive dysfunction, characterized by persistent confusion lasting weeks or months, which is more common in those undergoing cardiac surgery and in the elderly.