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. An anesthetic is an agent that causes anaesthesia. A patient under the effects of anesthesia is anesthetized. An anesthesiologist (US) or anaesthetist (UK) is a physician who performs anesthesia. A Certified Registered Nurse Anesthetist is an advanced practice nurse who performs anesthesia.