Chapter 14  ·  Module 2  ·  Visual Summary

Inhalational Anesthetic Agents

Comparative pharmacokinetics, distinguishing properties, and clinical selection

Comparative Pharmacokinetics

Ranked by Blood:Gas Partition Coefficient

Inhalational Agent Profiles

Agent Blood:Gas Coefficient Minimum Alveolar Concentration Induction Speed Key Distinguishing Feature
Desflurane ~0.42 ~6–7% Fastest Airway irritant — maintenance only; sympathetic surge on rapid increase; heated vaporizer required
Nitrous oxide ~0.47 ~104% Very fast Cannot produce surgical anesthesia alone; analgesic (N-methyl-D-aspartate antagonism); not a malignant hyperthermia trigger
Sevoflurane ~0.65 ~2.0% Fast Preferred pediatric induction agent; best bronchodilator; compound A at low flow; emergence agitation in children
Isoflurane ~1.4 ~1.17% Moderate Most widely used worldwide; vasodilation + reflex tachycardia (contrast halothane bradycardia)
Enflurane ~1.9 ~1.68% Slow Only epileptogenic volatile agent — contraindicated in seizure disorders
Halothane ~2.4 ~0.75% Slowest Catecholamine sensitization; immune hepatitis on re-exposure; bradycardia; myocardial depression

High-Yield Hazards by Agent

Halothane

Unique Adverse Effects

  • Catecholamine sensitization → ventricular arrhythmias with epinephrine
  • Immune-mediated hepatitis on re-exposure (trifluoroacetylated protein neoantigens)
  • Direct myocardial depression + bradycardia
  • Increases intracranial pressure (cerebral vasodilation)
  • Uterine relaxation → postpartum hemorrhage risk

Nitrous Oxide

Unique Adverse Effects

  • Expands air-filled cavities → pneumothorax, bowel obstruction, pneumocephalus, intraocular gas, middle ear
  • Vitamin B12 inactivation → megaloblastic anemia, subacute combined degeneration with prolonged use
  • Increases postoperative nausea and vomiting (duration-dependent)
  • Diffusional hypoxia on emergence (give oxygen)

Sevoflurane

Profile and Cautions

  • Non-pungent → preferred pediatric mask induction
  • Potent bronchodilator → preferred in asthma
  • Compound A from carbon dioxide absorbent degradation (low flow) → theoretical nephrotoxicity
  • Emergence agitation in children ages 2–5 (prevent with midazolam, propofol, fentanyl, dexmedetomidine)

Clinical Selection

Malignant hyperthermia susceptibility: avoid ALL volatile halogenated agents — use nitrous oxide or total intravenous anesthesia only.

Seizure disorder: absolutely avoid enflurane; sevoflurane and isoflurane preferred.

Pediatric induction: sevoflurane (non-pungent, fast, hemodynamically stable).

Fastest emergence (long/obese cases): desflurane (lowest tissue solubility, minimal accumulation).

Asthma / reactive airways: sevoflurane preferred; halothane acceptable where sevoflurane unavailable.

Air-filled space (pneumothorax, bowel obstruction, intraocular gas): avoid nitrous oxide.