A medical ventilator, commonly referred to as a respirator, is used to circulate breathable air into and out of the lungs when a patient is unable to do so on their own. They are commonly used in emergency rooms, intensive care units and operating rooms. Respirators are one of the most commonly used pieces of major medical equipment, and most people in industrialized countries are aware of at least one friend of family member whose breathing had to be supported by one at some point in their life. They are necessary for many patients under the influence of a general anesthetic.