How does general anesthesia work?

Drugs

Anesthesia is a medical treatment in which medications, known as anesthetics, are given to patients during surgery or other medical procedures that can be considered painful. These anesthetics provide pain relief by inducing a loss of sensation in a particular part of the body or the whole body.  They can also help induce a loss of consciousness and muscle relaxation, depending on the type of anesthesia.1 How does general anesthesia work?

Types of anesthesia

There are four types of anesthesia. These include sedation, local anesthesia, regional anesthesia, and general anesthesia. The choice of anesthesia depends on the type of procedure undertaken, length of the procedure, patient’s health, and preferences.

Local anesthesia

Local anesthesia involves numbing the pain in a particular part of the body upon which the medical procedure is performed.2 Patients given the drugs for local anesthesia, remain awake during the procedure. The drugs are either directly injected through the skin and tissues or applied on the skin, absorbing the medication. Local anesthesia is commonly used for dental procedures, biopsies, and minor surgeries.

Regional anesthesia

Regional anesthesia is a type of anesthesia in which pain in a specific region of the body is numbed.3 It is most commonly used in reproductive surgeries, childbirth as well as hand or foot surgeries. Like local anesthesia, patients stay awake during the surgical procedure. There are two types of regional anesthesia: epidural and spinal anesthesia.

General anesthesia

General anesthesia is a type of anesthesia in which the patient is unconscious during a surgical procedure that can take several hours to complete.4  It is commonly used for serious or major surgeries that can affect a person’s breathing or lead to significant loss of blood.5

General anesthesia involves using drugs called general anesthetics. These consist of a combination of different medications including sedatives, muscle relaxants, opioids (pain relief) and tranquilizers (lower anxiety)4,5. The anesthetics are usually administered by either IV (through the veins) or gas inhalation.

The general anesthetics work to induce unconsciousness and can lead to pain relief for the whole body, muscle relaxation and loss of movement.6 These physiological responses generally depend on the type and dosage of the medications used to produce anesthesia.7

In this article, we will provide a detailed overview of how general anesthesia works.

How does general anesthesia work?

Research indicates general anesthesia works by inhibiting transmission of nerve signals in the central nervous system. According to some studies, the anesthetics target neurotransmitters and proteins in the nerve cell membranes to induce unconsciousness, block pain as well as cause amnesia or loss of movement.7,8

A 2020 study, published in The Journal of Neuroscience, reported that a general anesthetic known as isoflurane is linked to decreased transmission of nerve signals responsible for controlling movement or cognition in rats.8 This study found that isoflurane, an anesthetic inhaled as gas, reduced the levels of neurotransmitters, suggesting that it can potentially induce the responses associated with anesthesia by inhibiting these signals. However, more research and clinical studies are needed to further understand the mechanisms of this general anesthetic.

In a 2018 study, published in Cell Reports, Propofol, a general anesthetic delivered through the veins, induces sedation or unconsciousness in patients by inhibiting the transmission of nerve signals in the brain. According to the researchers, this is done by blocking the release of the neurotransmitters and limiting movement of the Syntaxin1A protein in the nerve cell membrane.9 However, more research is needed to determine if this general anesthetic can potentially elicit other responses in the body during anesthesia.

Some studies suggest that certain responses of general anesthesia may be linked to particular regions in the brain and the central nervous system.7 The effects of sedation or unconsciousness may be linked to the neocortex and thalamus, while amnesia may be linked to the hippocampus.

Equipment for general anesthesia

An anesthesia machine is the equipment used for general anesthesia. This equipment includes a ventilator, gas supply system, breathing apparatus, vaporizers and suction equipment.5 It also has a monitor displaying the patient’s vital signs including blood pressure and heart rate.

The anesthesia machine works to prepare a mixture of gases and vapours needed for this procedure. This gas mixture, which includes oxygen are supplied from cylinders and delivered to the breathing apparatus via the vaporizer.10 The breathing apparatus can include a face mask, breathing tube, oral or nasal airway device, or a laryngoscope.5

Who is responsible for providing anesthesia?

Anesthesia care is provided by an anesthesiologist, a specially trained doctor before, during, and after surgery when the patient is then sent to the recovery room.4,6 The doctor is usually assisted by a nurse anesthetist as well as assistants specially trained to administer anesthesia.

The anesthesiologist discusses the details of the procedure with the patient during which they provide instructions on what the patient can eat or drink before their surgery.4 They also discuss with the patient about their medications and help determine what medications can be taken before surgery.

Risks and side effects of general anesthesia

Common side effects of general anesthesia include nausea and vomiting that generally occur immediately after the medical procedure.4 Other side effects may include sore throat, confusion, memory loss, chills, dizziness, and urinary retention.5 Patients may also be at risk of damage to their vocal cords, teeth, gums, and lips from the breathing tubes inserted through their mouth.4

Rare but more serious side effects include malignant hyperthermia (a muscle disease), heart attack, and stroke.4 Older patients or those with medical conditions such as high blood pressure, diabetics, heart disease, kidney problems, or lung disease are generally at increased risk of developing these side effects.

Talk to your doctor about your condition and any medications you are taking as that can potentially have an effect on the type of anesthesia you can be given.

                                                                                     

References

Pawson, Patricia & Forsyth, Sandra. (2008). Anesthetic agents. Small Animal Clinical Pharmacology. 83-112. 10.1016/B978-070202858-8.50007-5.

Torpy JM, Lynm C, Golub RM. Local Anesthesia. JAMA. 2011;306(12):1395. doi:10.1001/jama.306.12.1395

Torpy JM, Lynm C, Golub RM. Regional Anesthesia. JAMA. 2011;306(7):781. doi:10.1001/jama.306.7.781

Torpy JM, Lynm C, Golub RM. General Anesthesia. JAMA. 2011;305(10):1050. doi:10.1001/jama.305.10.1050

Smith G, D’Cruz JR, Rondeau B, et al. General Anesthesia for Surgeons. [Updated 2020 Aug 25]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK493199/

Siddiqui BA, Kim PY. Anesthesia Stages. [Updated 2021 Mar 7]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK557596/

Son Y. Molecular mechanisms of general anesthesia. Korean J Anesthesiol. 2010;59(1):3-8. doi:10.4097/kjae.2010.59.1.3

Han-Ying Wang, Kohgaku Eguchi, Takayuki Yamashita, Tomoyuki Takahashi. Frequency-dependent block of excitatory neurotransmission by isoflurane via dual presynaptic mechanisms. The Journal of Neuroscience, 2020; JN-RM-2946-19 DOI: 10.1523/JNEUROSCI.2946-19.2020

Bademosi AT, Steeves J, Karunanithi S, Zalucki OH, Gormal RS, Liu S, Lauwers E, Verstreken P, Anggono V, Meunier FA, van Swinderen B. Trapping of Syntaxin1a in Presynaptic Nanoclusters by a Clinically Relevant General Anesthetic. Cell Rep. 2018 Jan 9;22(2):427-440. doi: 10.1016/j.celrep.2017.12.054. PMID: 29320738.

Gurudatt C. (2013). The basic anaesthesia machine. Indian journal of anaesthesia, 57(5), 438–445. https://doi.org/10.4103/0019-5049.120138

Image by Sasin Tipchai from Pixabay 

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