📊 Inhalational Anesthetics

Overview

Inhalational anesthetics are chemicals that when inhaled can alter consciousness and potentially produce a state of general anesthesia. Commonly used inhalational anesthetics in the United States are sevoflurane, desflurane, isoflurane, and nitrous oxide. They produce a dose-dependent depression in the level of consciousness.

History

graph TD; A[Nitrous Oxide 1844]; B[fa:fa-biohazard Diethyl Ether 1846]; B-->C[fa:fa-biohazard Chloroform 1847]; D[fa:fa-explosion Cyclopropane 1925]; D-->E[fa:fa-biohazard Trichloroethene 1930]; G[Halothane 1956]; G-->H[Methoxyflurane 1960]; H-->I[Enflurane 1973]; I-->J[Isoflurane 1981]; J-->K[Desflurane 1992]; K-->L[fa:fa-baby Sevoflurane 1994];

Volatile Inhalational Anesthetics

Volatile anesthetics are liquid at atmospheric pressure and room temperature. They require a vaporizer to deliver them to the patient which is typically either a variable bypass vaporizer (sevoflurane, isoflurane, halothane) or a gas blender (desflurane). They produce general anesthesia by ……..

Minimum Alveolar Concentration

Minimum Alveolar Concentration (MAC) is the alveolar concentration at which 50% of patients will not demonstrate a motor response to a standard surgical stimulation. Individual patient factors will affect this value (see table below). Further derivations of this value have been estimated for different clinical outcomes. MAC-BAR & MAC-Awake are examples of such derivations.

MAC-BAR
The MAC value that blocks autonomic responses to surgical incision in 50% of patients.
MAC-Awake
The MAC value that suppresses a voluntary response to verbal command (i.e., eye-opening) in 50% of patients

Factors Affecting MAC 1

Factors Increasing MACFactors Decreasing MAC
Age < 40Age > 40
Chronic ETOH useAcute ETOH use
HypernatremiaHyponatremia
Hyperthermia*Hypothermia*
MC1R gene mutation (red hair)Elderly
Pregnancy
Anemia
Hypercarbia
Hypoxia
* - Nitrous Oxide not affected by temperature

How MAC affects HR

AgentMAC value that ↑ HR
Sevoflurane1.5
Isoflurane0.5
Desflurane1.0

Isoflurane

FFCFHCClOFCFH

Sevoflurane

FHF₃₃CCCOCH₂F

Desflurane

HFCFOHCFFCFF

Non-Volatile Inhalational Anesthetics

Xenon

Nitrous Oxide

NN≡=≡=≡NN==OO

  1. Lobo SA, Ojeda J, Dua A, et al. Minimum Alveolar Concentration. [Updated 2022 Oct 19]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK532974/ ↩︎

Last updated on Jan 26, 2023