Background and Identification
Anesthesia or anaesthesia is a state of controlled, temporary loss of sensation or awareness that is typically induced for medical purposes. Anesthesia may include analgesia (relief from or prevention of pain), amnesia (loss of memory), unconsciousness, and paralysis (muscle relaxation). Anesthesia allows the painless performance of medical procedures that would otherwise cause intolerable pain.
The main instrument in an inhalational anesthetic delivery system is called an anesthetic machine. An anesthetic machine includes vaporizers, ventilators, an anesthetic breathing circuit, pressure gauges, and a waste gas scavenging system. Anesthetic machines are designed to provide anesthetic gas at constant pressure and oxygen for breathing and to remove carbon dioxide or other waste anesthetic gases. Inhalational anesthetics are flammable, so various checklists have been developed to ensure the machine is ready for use, that electrical hazards are removed, and that safety measures are active. Intravenous anesthetics can be delivered either by an infusion pump or by bolus doses. Many other smaller instruments may be used for monitoring the patient. Modern anesthetic machinery is generally designed to be fail-safe to decrease the odds of catastrophic misuse of the machine.
Patients under general anesthesia require continuous physiological monitoring. In the United States, the American Society of Anesthesiologists (ASA) established a list of minimum monitoring guidelines for patients receiving general or regional anesthesia. The lists include electrocardiography (ECG), heart rate, inspired and expired gases, blood pressure, temperature, and oxygen saturation of the blood (pulse oximetry). For more invasive surgeries, monitoring may also include urine output, central venous pressure, pulmonary artery pressure, cardiac output, cerebral activity, and neuromuscular activity. Anesthetic machines generally include a range of integrated systems for the monitoring of several vital parameters.