Anesthesiology, anaesthesiology, or anaesthesia is the medical specialty concerned with the total perioperative care of patients before, during and after surgery.[1] It encompasses anesthesia, intensive care medicine, critical emergency medicine, and pain medicine.[2] A physician specialized in anesthesiology is called an anesthesiologist or anaesthetist, depending on the country.[3][4][5][6] In some countries, the terms are synonymous, while in other countries they refer to different positions and anesthetist is only used for non-physicians, such as nurse anesthetists. The core element of the specialty is the study and use of anesthesia to safely support a patient's vital functions through the perioperative period. Since the 19th century, anesthesiology has developed from an experimental area with non-specialist practitioners using novel, untested drugs and techniques into what is now a highly refined, safe and effective field of medicine. In some countries anesthesiologists comprise the largest single cohort of doctors in hospitals,[7][8] and their role can extend far beyond the traditional role of anesthesia care in the operating room, including fields such as providing pre-hospital emergency medicine, running intensive care units, transporting critically ill patients between facilities, and prehabilitation programs to optimize patients for surgery.