What characteristic should an inhalation anesthetic agent have to anesthetize most quickly?

Inhalation Anesthetic Agent Characteristics for Rapid Anesthetization

An inhalation agent with a low blood:gas partition coefficient will anesthetize most quickly, as this property allows for rapid equilibration between alveolar and brain concentrations.

Understanding Blood:Gas Partition Coefficients and Speed of Induction

• The speed of induction with inhalation anesthetics is primarily determined by their blood:gas partition coefficient - the lower this value, the faster the onset of anesthesia 1, 2
• Low blood solubility allows for rapid equilibration between alveolar concentration and brain concentration, leading to faster induction 1
• This physical property is more important than the specific receptor mechanism (such as GABA modulation) when considering speed of onset 2

Comparing Available Inhalation Agents

• Desflurane has the lowest blood:gas partition coefficient (0.42) of all available volatile anesthetics, even slightly lower than nitrous oxide 2
• Sevoflurane has a low blood:gas partition coefficient, making it also suitable for rapid induction, especially in pediatric patients 1, 3
• Comparative studies show that:
  • Sevoflurane provides more rapid induction than halothane in both pediatric and adult patients 3
  • Desflurane offers the fastest emergence from anesthesia due to its extremely low solubility 4, 2

Clinical Considerations for Pediatric Patients

• Despite desflurane having the lowest blood:gas partition coefficient, its extreme pungency makes it unsuitable for mask induction in children 4, 2
• Sevoflurane is preferred for pediatric induction due to its:
  • Low pungency and non-irritant odor 1
  • Rapid and smooth induction properties 1
  • Better patient acceptability compared to other agents 1

Application to the Case Scenario

• For the 9-year-old boy with cerebral palsy requiring rapid anesthesia by mask:
  • An agent with low blood solubility would be most appropriate for rapid onset 1, 3
  • Sevoflurane would be the preferred agent due to its combination of low blood:gas partition coefficient and low airway irritability 1
  • Desflurane, while having the lowest blood:gas coefficient, would cause significant airway irritation during mask induction 4, 2

Important Considerations and Caveats

• While speed of induction is important, other factors must be considered:
  • Airway reactivity (coughing, laryngospasm) is higher with desflurane compared to sevoflurane 2
  • Cardiovascular stability may be better with sevoflurane 5
  • Rapid emergence can lead to earlier and more intense postoperative pain 1
• For pediatric patients specifically, the French guidelines for airway management under anesthesia recommend controlled induction techniques to decrease risks of hypoxemia and hemodynamic complications 6