Which maneuver would NOT increase the rate of an inhalation induction?

Which maneuver would NOT increase the rate of an inhalation induction?

• A. Increasing alveolar ventilation
• B. Substitution of desflurane for isoflurane
• C. Overpressurizing
• D. Placement of patient on an inotropic infusion

Answer: (D)

Inhalation induction rate is mainly governed by how quickly the alveolar concentration of the anesthetic rises to a level that produces brain uptake. Factors that speed this up include increasing alveolar ventilation (more fresh gas reaching the alveoli), using an agent with lower blood-gas solubility (less soluble agents reach brain faster), and raising the inspired concentration to create a greater driving gradient (overpressurizing). Substituting desflurane for isoflurane speeds induction because desflurane has a lower blood-gas solubility, so it is taken up into the blood less readily and reaches the brain more quickly. Increasing alveolar ventilation does this by delivering more anesthetic per unit time to the alveoli. Overpressurizing raises the partial pressure of the anesthetic in the alveoli, accelerating the rise in brain-penetrating concentrations. However, placing the patient on an inotropic infusion increases cardiac output. This boosts tissue and venous uptake of the anesthetic, effectively increasing the amount of drug drawn into the circulation and tissues. That enhanced uptake slows the rise of alveolar concentration, so it does not speed up the induction.

Inhalation induction rate is mainly governed by how quickly the alveolar concentration of the anesthetic rises to a level that produces brain uptake. Factors that speed this up include increasing alveolar ventilation (more fresh gas reaching the alveoli), using an agent with lower blood-gas solubility (less soluble agents reach brain faster), and raising the inspired concentration to create a greater driving gradient (overpressurizing).

Substituting desflurane for isoflurane speeds induction because desflurane has a lower blood-gas solubility, so it is taken up into the blood less readily and reaches the brain more quickly. Increasing alveolar ventilation does this by delivering more anesthetic per unit time to the alveoli. Overpressurizing raises the partial pressure of the anesthetic in the alveoli, accelerating the rise in brain-penetrating concentrations.

However, placing the patient on an inotropic infusion increases cardiac output. This boosts tissue and venous uptake of the anesthetic, effectively increasing the amount of drug drawn into the circulation and tissues. That enhanced uptake slows the rise of alveolar concentration, so it does not speed up the induction.