Anesthetic
An anesthetic (
A wide variety of drugs are used in modern anesthetic practice. Many are rarely used outside
Local anesthetics
Ester-based
- Benzocaine
- Cocaine (historical)
- Procaine
- Amethocaine)
Amide-Based
Local anesthetic agents prevent the transmission of nerve impulses without causing unconsciousness. They act by reversibly binding to fast
Local anesthetics can be either
Only
Pethidine also has local anesthetic properties, in addition to its opioid effects.[7]
General anesthetics
Inhaled agents
- Desflurane (common)
- Enflurane (largely discontinued)
- Halothane (inexpensive, discontinued)
- Isoflurane (common)
- Methoxyflurane
- Nitrous oxide
- Sevoflurane (common)
- Xenon (rarely used)
No anaesthetic agent currently in use meets all these requirements, nor can any anaesthetic agent be considered completely safe. There are inherent risks and drug interactions that are specific to each and every patient.[9] The agents in widespread current use are isoflurane, desflurane, sevoflurane, and nitrous oxide. Nitrous oxide is a common adjuvant gas, making it one of the most long-lived drugs still in current use. Because of its low potency, it cannot produce anesthesia on its own but is frequently combined with other agents. Halothane, an agent introduced in the 1950s, has been almost completely replaced in modern anesthesia practice by newer agents because of its shortcomings.[10] Partly because of its side effects, enflurane never gained widespread popularity.[10]
In theory, any inhaled anesthetic agent can be used for induction of general anesthesia. However, most of the halogenated anesthetics are irritating to the airway, perhaps leading to coughing, laryngospasm and overall difficult inductions. If induction needs to be conducted with an inhaled anesthetic agent, sevoflurane is often used due to a relatively low pungency, rapid increase in alveolar concentration, and a higher blood solubility than other agents. These properties allow for a less irritating and quicker induction as well as a rapid emergence from anesthesia compared to other inhaled agents.[4] All of the volatile agents can be used alone or in combination with other medications to maintain anesthesia (nitrous oxide is not potent enough to be used as a sole agent).
Volatile agents are frequently compared in terms of potency, which is inversely proportional to the
Intravenous agents (non-opioid)
While there are many drugs that can be used intravenously to produce anesthesia or sedation, the most common are:
- Barbiturates
- Amobarbital (trade name: Amytal)
- Methohexital (trade name: Brevital)
- Thiamylal (trade name: Surital)
- Thiopental (trade name: Penthothal, referred to as thiopentone in the UK)
- Benzodiazepines
- Etomidate
- Ketamine
- Propofol
Among the barbiturates mentioned above,
Among the barbiturates mentioned above, thiopental and methohexital are ultra-short-acting and are used to induce and maintain anesthesia is one of the most commonly used intravenous drugs employed to induce and maintain general anesthesia.[11] It can also be used for sedation during procedures or in the ICU.[11] Like the other agents mentioned above, it renders patients unconscious without producing pain relief.[11] Compared to other IV agents, etomidate causes minimal depression of the cardiopulmonary system. Additionally, etomidate results in a reduction in intracranial pressure and cerebral blood flow.[4] Because of these favorable physiological effects, was a favored agent in the ICU. However, etomidate has since been shown to produce adrenocortical suppression, resulting in decreased use to avoid an increased mortality rate in severely ill patients.[4] Ketamine is infrequently used in anesthesia because of the unpleasant experiences that sometimes occur on emergence from anesthesia, which include "vivid dreaming, extracorporeal experiences, and illusions."[12] When it is used, it is often paired with a benzodiazepine such as midazolam for amnesia and sedation.[4] However, like etomidate it is frequently used in emergency settings and with sick patients because it produces fewer adverse physiological effects.[11] Unlike the intravenous anesthetic drugs previously mentioned, ketamine produces profound pain relief, even in doses lower than those that induce general anesthesia.[11] Also unlike the other anesthetic agents in this section, patients who receive ketamine alone appear to be in a cataleptic state, unlike other states of anesthesia that resemble normal sleep. Ketamine-anesthetized patients have profound analgesia but keep their eyes open and maintain many reflexes.[11]
Intravenous opioid analgesic agents
While opioids can produce unconsciousness, they do so unreliably and with significant side effects.[13][14] So, while they are rarely used to induce anesthesia, they are frequently used along with other agents such as intravenous non-opioid anesthetics or inhalational anesthetics.[11] Furthermore, they are used to relieve pain of patients before, during, or after surgery. The following opioids have short onset and duration of action and are frequently used during general anesthesia:
- Alfentanil
- Fentanyl
- Remifentanil
- Sufentanil, which is not available in Australia.
The following agents have longer onset and duration of action and are frequently used for post-operative pain relief:
- Buprenorphine
- Butorphanol
- Diamorphine, also known as heroin, not available for use as an analgesic in any country but the UK.
- Hydromorphone
- Levorphanol
- Pethidine, also called meperidine in North America.
- Methadone
- Morphine
- Codeine
- Nalbuphine
- Oxycodone, not available intravenously in U.S.
- Oxymorphone
- Pentazocine
Muscle relaxants
Muscle relaxants do not render patients unconscious or relieve pain. Instead, they are sometimes used after a patient is rendered unconscious (induction of anesthesia) to facilitate
- Depolarizing muscle relaxants
- Succinylcholine(also known as suxamethonium in the UK, New Zealand, Australia and other countries, "Celokurin" or "celo" for short in Europe)
- Decamethonium
- Non-depolarizing muscle relaxants
- Short acting
- Mivacurium
- Rapacuronium
- Intermediate acting
- Atracurium
- Cisatracurium
- Rocuronium
- Vecuronium
- Long acting
- Alcuronium
- Doxacurium
- Gallamine
- Metocurine
- Pancuronium
- Pipecuronium
- Tubocurarine
- Short acting
A potential complication where neuromuscular blockade is employed is '
Intravenous reversal agents
- Flumazenil, reverses the effects of benzodiazepines
- Naloxone, reverses the effects of opioids
- Neostigmine, helps to reverse the effects of non-depolarizing muscle relaxants
- Sugammadex, helps to reverse the effects of non-depolarizing muscle relaxants
References
- PMID 6385930– via jamanetwork.com.
- ^ Karch, SB (1998). A brief history of cocaine. CRC press.
- ISBN 978-3527306732.
- ^ ISBN 978-0-07-171405-1.
- S2CID 8125002.
- ^ "Reducing Animals' Pain and Distress | National Agricultural Library". www.nal.usda.gov. 2022. Retrieved 28 January 2023.
- S2CID 23410891.
- ISBN 978-3527306732.
- PMID 16100238.
- ^ ISBN 0-7216-5368-5.
- ^ ISBN 0-443-06656-6.
- S2CID 2526481.
- PMID 2141773.
- S2CID 32056642.
External links
- Anaesthetics, BBC Radio 4 discussion with David Wilkinson, Stephanie Snow & Anne Hardy (In Our Time, Mar. 29, 2007)