Anesthetic describes any substance which prevents a person from feeling pain. They differ from painkillers, which merely lessen the effect of pain. The study of and medical speciality regarding anesthetics is anesthesiology. A specialist in the field is an anesthesiologist.
Anesthetics come in two types:
Local, such as novocain. Local anesthetics work by blocking nerve impulses in the area where the anesthetic is administered. These are useful for such work as stitching up wounds or working on teeth. Local anesthetics are usually quite safe and do not require any special preparation of the patient.
General, such as nitrous oxide. General anesthetics work by making the patient unconscious and suppressing that part of the brain that processes pain signals. These are useful for major surgery where it is expected that the patient will be operated on for more than a short period of time. However, general anesthetics have numerous complications, the most serious of which is nausea which can result in vomitting if the patient has eaten. As such, they can only be used on patients who have not recently eaten. In addition, the longer the patient is under general anesthesia, the more difficult it is to bring them out of the anesthetic induced unconsciousness. The mechanism of general anesthetics is still poorly understood, but they appear to interfere with mulitple pathways in the nervous system, which would also account for their numerous side effects.
History
Before the discovery of anesthetic substances in the mid 19th century, surgical procedures were limited to those that could be performed quickly so that the patient would not die of the shock resulting from the pain and blood loss resulting from the surgery. For example, amputation was generally accomplished in less than two minutes and the speed of the surgeon's scalpel was as important as his knowledge of anatomy. The best a patient could hope for was laudanum, a mixture of alcohol (usually wine or brandy) and opium.
Nitrous oxide had been known for some time for it's intoxicating effect, and several medical professionals independently noted that persons who accidentally hurt themselves while under its effects felt no pain from the experience. Dentists were the first ones to make practical use of the gas in order to treat their patients. However, the medical community was slow to adopt nitrous oxide as its effect on patients was often unpredictable and some patients continued to feel pain.
Ether was the next anesthetic to be discovered, but it too had several drawbacks. Although it always induced unconsciousness, it was difficult to control the dosage, resulting in many accidental overdoses. It also made patients very nauseous.
Ironically, the use of anesthetics increased the mortality rate of patients as many developed infections after surgery. It was only after the development of antiseptic operating rooms in the late 19th century that surgery became a generally safe way of treating illness.