Anesthesiology is a term used to describe the medical speciality concerned with the study of anesthesia or anesthetics. Anesthesia by definition is the loss of sensation with or without the loss of consciousness. The American Society of Anesthesiologists define anesthesiology as "the practice of medicine dedicated to the relief of pain and total care of the surgical patient before, during and after surgery."
|Focus||Anesthesia, perioperative medicine|
Terminology varies between countries. In North America, the specialty is called anesthesiology, and can be administered by a medical doctor, a certified registered nurse anesthetist (an advanced practice nurse), or an anesthesiologist assistant (a non-physician provider who practices anesthesia under the direction of an anesthesiologist. By contrast, in the United Kingdom and other countries following the British tradition, both the medical specialty and the treatment delivered are referred to as anaesthesia or anaesthetics, and the physician who performs them is termed an anaesthetist. Though a general term, the word anesthetist can be used for any practitioner providing anesthesia services, but colloquially in North America it generally indicates a certified registered nurse anesthetist, whereas the term "anesthesiologist" usually refers to a medical doctor.
Over the past 100 years, the study and administration of anesthesia has become more complex. Historically anesthesia providers were almost solely utilized during surgery to administer general anesthesia in which a person is placed in a pharmacologic coma. This is performed to permit surgery without the individual responding to pain (analgesia) during surgery or remembering (amnesia) the surgery.
However, thanks to the advances is medicine, many procedures or diagnostic tests do not require "general anesthesia" and can be performed using various forms of sedation or regional anesthesia, which can be performed to induce analgesia in a region of the body. For example, epidural administration of a local anesthetic is commonly performed on the mother during childbirth to reduce labor pain while permitting the mother to be awake and active in labor & delivery.
In the United States, anesthesiologists may also perform non-surgical pain management (termed pain medicine) and provide care for patients in intensive care units (termed critical care medicine). Certified registered nurse anesthetists may also perform non-surgical pain management.
In the United States, anesthesiologists attend four years of medical school to earn either a Doctor of Medicine (MD) degree or a Doctor of Osteopathic Medicine (DO) degree and then follow it with four years of residency. Certified Registered Nurse Anesthetists or CRNAs are advanced practice registered nurses with additional post-graduate training in anesthesia. By 2025, all CRNA programs will require a doctorate degree. In the United States, the most common anesthesia care model is where an anesthesiologist and Certified Registered Nurse Anesthetist work as a team (termed medical direction or medical supervision). In 17 states, CRNAs can practice without the supervision of a physician (though physician does not dictate it be an anesthesiologist). 
Effective practice of anesthesiology requires several areas of knowledge by the practitioner, some of which are:
- Pharmacology of commonly used drugs including inhalational anaesthetics, topical anesthetics, & vasopressors as well as numerous other drugs used in association with anesthetics (e.g., ondansetron, glycopyrrolate)
- Monitors: electrocardiography, electroencephalography, electromyography, entropy monitoring, neuromuscular monitoring, cortical stimulation mapping and neuromorphology
- Mechanical ventilation
- Anatomical knowledge of the nervous system for nerve blocks, etc.
- Other areas of medicine (e.g., cardiology, pulmonology, obstetrics) to assess the risk of anesthesia to adequately have informed consent, and knowledge of anesthesia regarding how it affects certain age groups (neonates, pediatrics, geriatrics)