The Five Senses and Beyond: The Encyclopedia of Perception - Jennifer L. Hellier 2017


Anesthesia is a pharmacologically induced and reversible loss of responsiveness. It is used in surgery or other procedures to block pain sensations in patients. The word anesthesia is derived from Greek meaning “without sensation” and is used to describe the state of analgesia (meaning painless or numbness). These effects can be from a single drug or a combination of drugs that provides a very specific combination of effects depending on the surgical needs.


During ancient Greek and Roman periods, some plants (like opium) were known to provide euphoric effects as well as make a person unconscious. It was this knowledge that 12th-century Arab physicians used to develop the first documented inhaled anesthetic. It was said that a sponge soaked in a dissolved solution of opium, mandragora, hemlock juice, and other substances would be dampened and placed under the nose of the patient just prior to surgery. However, the amounts had to be regulated as too much of the solution could cause death.

In the following centuries, volatile liquids and gases were developed for inhalational anesthetics including ether (previously known as “sweet vitriol”), nitrous oxide (also known as “laughing gas”), and chloroform. It is well documented that English physician John Snow (1813—1858) used chloroform in 1853 to anesthetize Queen Victoria during the birth of her eighth child, Prince Leopold. Dr. Snow is also noted as one of the first physicians to calculate the doses needed for successful surgical anesthesia for chloroform and ether as well as developing the equipment used to volatilize liquids into inhaled gases.

Types of Anesthesia

Volatile liquids, inhaled gases, and some manmade drugs are used as anesthetics. Specifically, the goal of an anesthetic is to provide a reversible loss of responsiveness, meaning putting a person, body part, or body region “to sleep” that will eventually wake up. The reversible loss of responsiveness may include the loss of muscle reflexes, the loss of sensation, and a decreased stress response. Some anesthesia may induce all of the above.

Within medicine, there is a specialty called anesthesiology in which the physician is an expert at putting patients to sleep for the surgery and then waking them up at the end of the procedure. An anesthesiologist may also be called an anesthetist, meaning a person who professionally administers anesthesia. Because of the delicate procedure of inducing a reversible loss of responsiveness, anesthesiologists must constantly monitor patients’ breathing, heart rate, blood pressure, and body temperature so that they will not have complications while under anesthesia.

Today there are four main types of anesthesia: local, regional, general, and dissociative. Local anesthesia is mostly used when a specific location on the body needs to have no sensation. For example, local anesthesia is used by dentists to fill a cavity in a tooth, by podiatrists to remove a toenail, or by dermatologists to remove a mole on the skin.

Regional anesthesia is used to block sensation to a region of a body, such as the lower half of the body. Regional anesthesia is used during an epidural or a spinal block. The anesthetic is injected within the spinal column space below the spinal cord, which blocks the transmission of nerve signals to the spinal cord. This is the preferred method of anesthesia during a Caesarean section (C-section) for complicated childbirths.

General anesthesia is performed when a person undergoes major surgery as it renders a person unconscious with no sensation. This occurs by inhibiting the sensory and motor functions of the peripheral and central nervous systems as well as blocking the sympathetic division of the autonomic nervous system. General anesthesia would be used during knee surgery as well as during heart surgery.

Finally, dissociative anesthesia is used when the higher brain regions need to be disassociated from the lower brain regions, causing the person to feel detached from the environment. These types of drugs are also called hallucinogens because they alter the perception of sight and sound while putting the person in a dream-like state. Hallucinogens may be used in combination with other drugs to help induce general anesthesia.

Modern Anesthesiology

Today, anesthesiologists must understand how to use the complex equipment needed for the different types of anesthetics as well as how to properly calculate doses for the correct level of anesthesia for the patient. Since a person can die from the anesthesia, the American Society of Anesthesiologists (ASA) has established minimum guidelines for monitoring patients under anesthesia to reduce the chance of death. These include measuring the electrographic activity of the heart, heart rate, blood pressure, breathing rates (inspired and expired gases), saturation of oxygen within the blood, and body temperature.

Patricia A. Bloomquist

See also: Autonomic Nervous System; Central Nervous System; Discriminative Touch; Nociception; Peripheral Nervous System; Peripheral Neuropathy

Further Reading

Smith, Eckehard A., Astrid G. Stucke, & Edward J. Zuperku. (2012). Effects of anesthetics, sedatives, and opioids on ventilatory control. Comprehensive Physiology, 2(4), 281—367.