General Anesthetics: The Different Types

General anesthetics can be administered by inhalation or intravenously. Only a healthcare professional can administer a general anesthetic. These substances have unwanted side effects that need to be controlled in order to avoid complications.

General anesthetics are drugs administered in the operating room to cause, as the name suggests, general anesthesia. This state corresponds to a progressive and controlled depression of the functions of the central nervous system.

When a patient is under the effect of a general anesthetic, he or she loses consciousness and is unresponsive to painful stimuli. These two effects are reversible.

The choice of general anesthetic will vary depending on the end goal to be achieved. But in general, all general anesthetics are intended to cause the following effects:

• Insensitivity to pain
• Loss of reflexes
• Complete amnesia during surgery
• Musculoskeletal relaxation
• Loss of consciousness

All of these effects occur in different places within the central nervous system. This means that to get all of these effects from just one drug, the dose must be very high. This is why healthcare professionals use combinations to avoid irreversible depression of vital areas of the brain.

The characteristics of general anesthesia

Despite the great advances in science in this area, it is not yet clear which structures are affected and which molecules anesthetics act on. We only know that they cause sedation and hypnosis by profoundly modifying many processes.

Here are some hypotheses put forward by the researchers:

• General anesthetics have a non-specific action on the properties of the neuronal membrane
• Meyer and Overton’s lipid theory : these drugs act on lipid targets, i.e. on fats and, therefore, their potency would depend on their solubility in these fats
• General anesthetics act on receptor proteins or ion channels
• These substances are involved in the action of voltage- gated channels and ion channels

In addition, when administering a general anesthetic, the following three factors must be taken into consideration:

• Rate at which the substance causes general anesthesia
• Duration of anesthesia for a specific dose
• Power, depth and intensity of anesthesia

General inhalation anesthetics

These general anesthetics are substances which, when inhaled through the airways, produce general anesthesia. They are not irritant drugs and are typically used with intravenous inducers to maintain anesthesia.

The anesthetic potency of these drugs depends on the partial pressure or the tension that the anesthetic manages to reach in the brain. Usually, this pressure should be close to partial pressure in the blood.

Here are some general inhalation anesthetics:

• Nitrous oxide
• Halothane
• Isoflurane
• Desflurane
• Sé voflurane

All of these drugs pass through the mucous membranes to the brain. Their absorption or diffusion takes place in three stages:

1. Pulmonary inhalation stage : the induction speed of less soluble anesthetics is higher, which means that with more soluble anesthetics the anesthesia is slower
2. Distribution in tissues
3. Elimination

Intravenous general anesthetics

The purpose of intravenous anesthetics is to induce and maintain anesthesia just before surgery. These substances have hypnotic, analgesic, anxiolytic and relaxing properties in the muscles.

Intravenous anesthesia allows the patient to be quickly anesthetized, but it is less easily controlled than that by inhalation. Anesthesia specialists use the infusion rate parameter to meet the conditions for clinical anesthesia.

Here are some general intravenous anesthetics:

• Thiopental sodium
• Propofol
• Etomidate
• Ketamine

All of these drugs can cause unwanted side effects such as respiratory depression, apnea, muscle stiffness, blurred vision, and mood swings, among others.

Anesthesia, a medical process

General anesthesia is a delicate process, which is why it requires special attention : the misuse of general anesthetics (dose administered, type of anesthetic, etc.) can lead to the death of the patient.

Today’s doctors have access to a wide variety of general anesthetics that have fewer side effects and less risk.