Anesthetic Agents Overview

Anesthetic Agents Overview

  • Two main types: Inhaled agents, IV anesthetic agents.

History of Anesthesia

  • Ancient use: coca leaves, opium poppy since 1500 BC.

  • Nitrous oxide, diethyl ether, chloroform discovered in the 1840s.

  • Local anesthesia with cocaine (1885), endotracheal tube (1878), thiopental (1934).

Goals of Anesthesia

  • Achieve unconsciousness, analgesia, and muscle relaxation.

Definitions

  • General Anesthesia: Loss of consciousness; unresponsive even to pain.

  • Inhalational Agents: Produce anesthesia via gases or vapors.

  • Analgesic: Pain relief without loss of consciousness.

Inhaled Agents

  • Aim: Maintain partial pressure in the brain.

  • Uptake: From alveoli to the brain via capillaries.

  • MAC (Minimum Alveolar Concentration): Concentration that prevents movement in 50% of patients.

Classes of Inhaled Agents

  • Gases: Nitrous Oxide, Xenon.

  • Vapors: Sevoflurane, Isoflurane, Desflurane, Halothane.

Inhaled Agent Properties

  • Potency and Solubility: Higher solubility = slower uptake.

  • Halothane: Most potent; MAC 0.75.

  • Desflurane: Fast onset/offset; MAC 6.6.

Mechanisms of Action

  • Believed to act via GABA A receptors in the CNS.

Nitrous Oxide

  • Properties: Weak anesthetic, powerful analgesic.

  • MAC 104%, low solubility, caution in certain surgeries.

Halothane

  • MAC 0.75%; side effects include myocardial depression and respiratory drive reduction.

Isoflurane and Sevoflurane

  • Isoflurane: Common in cardiac surgeries; MAC 1.1%.

  • Sevoflurane: Rapid induction/emergence; MAC 2.1%.

Desflurane

  • MAC 6.6%; pungent odor, fast uptake, and potential for laryngospasm.

Malignant Hyperthermia

  • Triggered by potent volatile anesthetics and succinylcholine.

  • Symptoms: Increased CO2, muscle rigidity, tachycardia.

  • Treatment includes stopping agents, administering dantrolene, and cooling.

IV Anesthetics Classification

  • Induction agents: Propofol, Benzodiazepines, Barbiturates, Etomidate, Ketamine.

Propofol

  • Rapid sedation and antiemetic; acts on GABA A receptors.

  • Cardiac depression effects and decreases cerebral blood flow.

Barbiturates

  • Include Thiopental; acts on GABA A receptors, short duration.

  • Potential for respiratory depression and vascular issues.

Benzodiazepines

  • Common agents: Midazolam, Lorazepam, Diazepam.

  • GABA A receptor action, minimal cardiac effects.

Ketamine

  • Dissociative anesthetic; NMDA receptor antagonist; promotes analgesia with minimal respiratory effects.