Without talking about all the details of all the different theories, general anesthetics work at the level of the spinal cord (resulting in relaxation of the muscles) and at different areas of the brain. These anesthetic drugs can be given to the patient either as an inhaled gas or injected into the intravascular line (directly into the patient's bloodstream)..

When medications reach the bloodstream to be carried to the brain, they are also carried to other organs (for example, the heart) and have effects at these other organs as well. Therefore, part of anesthesia is the careful monitoring of the patient in order to monitor and control these other effects.

Each medication has its own effects, side effects, duration of action, etc. Often, multiple types of medication are combined to achieve the desired results in a given situation. The amount of anesthesia that a patient needs is determined by multiple factors and the individual patient's needs. A knowledge of the potency of each medication helps determine how much of each drug to give to the patient.

The potency of an inhaled anesthetic is quantified by its "MAC" or Minimum Alveolar Concentration. The alveolus is the area of the lung in which gas leaves the lung and enters the bloodstream. MAC is defined as the amount of gas in the lungs required to prevent fifty percent of humans from moving when given a painful stimulus like a surgical incision. Intravenous medications can be characterized as to their "equivalent MAC" so that their potencies can be compared to the inhaled medications.

Are there any other medications that are used?
There are other medications in anesthesia that are used to achieve specific goals that assist with the performance of the surgery or are important to patient comfort. For example, sometimes medications are used that specifically block the contraction of muscles, resulting in complete muscle relaxation.

Another example are medications that are often given to prevent the patient from having nausea after the operation. Medications such as this are not required for the patient to be pain-free or for the surgeons to work, but obviously can contribute a great deal to the patient's comfort and satisfaction.

Medications such as these are not always required and may not always be used. If you have questions about what medications are to be used for your specific situation should be discussed with your anesthesiologist or nurse anesthetist.