Why is anesthetic not used when a patient has a fever?

General anesthetic can be used when a patient has a fever, although no elective surgery will be done if an infection is present. Usually they will try to control or eliminate the infection prior to surgery. Also, a life-threatening adverse reaction to one of the general anesthetics is called Malignant Hyperthermia. In this rare situation the patients body temp. rises quickly to dangerous levels and must be treated agressively to prevent brain damgae and/or death, so if the patient already has a fever, this would be harder to detect. If you are referring to local anesthetic such as Lidocaine, it does not work if there is infection/inflammation present, such as a dental abcess.