General Anesthetics and Related Agents – Vocabulary Flashcards

Key vocabulary terms and concise definitions related to General Anaesthetics, inhalational and intravenous agents, techniques, and related pharmacology from the notes.

General anaesthetics (GAs)

Drugs that produce reversible loss of all sensation and consciousness; used in modern practice as part of balanced anaesthesia to achieve analgesia, amnesia, immobility, and reflex abolition.

MAC (Minimal Alveolar Concentration)

The lowest concentration of an inhaled anaesthetic in the alveoli that prevents movement in 50% of patients in response to a surgical stimulus; a standard measure of potency for inhalational GAs.

Oil:Gas partition coefficient

Ratio indicating how soluble an anaesthetic is in oil (lipids) relative to gas; higher values imply greater lipid solubility and CNS entry, correlating with potency for some GAs.

Blood:Gas partition coefficient (λ)

Ratio of anaesthetic concentration in blood to that in the gas at equilibrium; a measure of solubility in blood affecting induction and recovery rates.

Unitary hypothesis

Old idea that a single common molecular mechanism accounts for all inhalational anaesthetics' action (now replaced by agent-specific theories).

Agent-specific theory

Current view that different general anaesthetics act by different molecular mechanisms rather than a single shared mechanism.

GABAA receptor–Cl− channel

A ligand-gated ion channel targeted by many anaesthetics; enhances inhibitory GABAergic transmission leading to Cl− influx and neuronal hyperpolarization.

NMDA receptor

Excitatory glutamate receptor that certain agents (e.g., ketamine, nitrous oxide) preferentially inhibit, contributing to anaesthetic effects.

Two-pore domain K+ channels

A type of potassium channel implicated in GA-induced neuronal hyperpolarization and reduced transmitter release.

Second gas effect

Increased CNS uptake of a second inhaled anaesthetic when used with high concentrations of N2O during induction.

Diffusion hypoxia

Hypoxia caused by rapid diffusion of N2O out of the blood into the alveoli after stopping N2O, prevented by 100% oxygen briefly after discontinuation.

Open drop method

Simple inhalation technique where liquid anaesthetic is poured over a mask; vapour inhaled with air; imprecise concentration control.

Open system (inhalation anaesthesia)

Anaesthetic circuit where exhaled gases exit through a valve and fresh non-rebreathing mixture is inhaled; high drug consumption, precise control possible.

Closed system (inhalation anaesthesia)

Rebreathing system where exhaled gases pass through soda lime to absorb CO2; low fresh gas flow and lower drug loss; useful for costly agents.

Semiclosed system

Partial rebreathing system with intermediate fresh gas flow; intermediate control over inspired anaesthetic concentration.

Ether (Diethyl ether)

Volatile inhalational anaesthetic, highly soluble in blood; potent but unpleasant, flammable; slow induction and recovery.

Halothane

Volatile inhalational anaesthetic with intermediate blood solubility; potent; can depress myocardium and respiration; rare hepatitis risk.

Isoflurane (Forane)

Inhalational GA with rapid induction/recovery, less myocardial depression than halothane; widely used for maintenance.

Desflurane

All-fluorinated inhalational anaesthetic with very low blood solubility; very rapid induction/recovery; pungent odour and airway irritation risk.

Sevoflurane (Sevorane)

Fluorinated inhalational anaesthetic with fast induction/recovery, non-irritant and pleasant; suitable for pediatric induction; higher cost.

Thiopentone (Thiopentone sod.)

Ultra-short-acting IV barbiturate used for rapid induction of anaesthesia; rapid brain entry but redistribution and metabolism terminate action.

Propofol

Ultra-short-acting IV agent used for induction and often maintenance of anaesthesia; rapid distribution and recovery; not irritant to airways.

Etomidate

IV induction agent with minimal cardiovascular and respiratory depression; often used in patients with cardiac risk.

Benzodiazepines in anaesthesia

IV hypnotics/premedication (e.g., diazepam, lorazepam, midazolam) that provide sedation, amnesia; reversed by flumazenil if needed.

Flumazenil

Competitive antagonist at the BZD site; reverses benzodiazepine effects and can treat BZD overdose or BZD-induced sedation.

Ketamine

Dissociative anaesthesia agent; NMDA receptor antagonist; preserves respiration, bronchodilates; produces analgesia and profound amnesia with dissociation.

Fentanyl

Potent, lipophilic opioid suitable for intraoperative analgesia; rapid onset with short duration; significant respiratory depression risk.

Naloxone

Opioid antagonist used to reverse opioid effects (analgesia, respiratory depression) in overdose or overdose-related coma.

Conscious sedation

Monitored state of reduced consciousness where patient remains responsive and maintains airway; combines local/regional anaesthesia with sedatives/anxiolytics.

Dissociative anaesthesia

Anaesthetic state (often due to ketamine) where patient appears awake but dissociated from surroundings, with analgesia and amnesia but preserved reflexes.

Epidural/Intrathecal analgesia

Analgesia delivered around spinal cord via epidural or intrathecal routes; allows pain relief with preserved consciousness depending on agents used.