Which statement describes the effect of increasing cardiac output on the rate of inhalation induction?

Which statement describes the effect of increasing cardiac output on the rate of inhalation induction?

• A. It speeds induction
• B. It slows induction
• C. It has no effect
• D. It speeds induction only with high oxygen content

Answer: (B)

Increasing cardiac output slows the rate of inhalation induction. When more blood is flowing through the lungs, a larger volume of the anesthetic is taken up into the blood before the alveolar gas builds up to a high partial pressure. This means the alveolar and arterial concentrations rise more slowly, delaying the amount of drug that reaches the brain and lengthening the time to full unconsciousness. The effect is especially noticeable with agents that are more soluble in blood, because they don’t stay in the alveoli as long and are more readily drawn into the bloodstream. Conversely, lower cardiac output speeds induction because less blood is available to take up the anesthetic, allowing the alveolar concentration to rise more quickly. The oxygen content of the inspired gas isn’t the primary driver of this uptake rate.

Increasing cardiac output slows the rate of inhalation induction. When more blood is flowing through the lungs, a larger volume of the anesthetic is taken up into the blood before the alveolar gas builds up to a high partial pressure. This means the alveolar and arterial concentrations rise more slowly, delaying the amount of drug that reaches the brain and lengthening the time to full unconsciousness. The effect is especially noticeable with agents that are more soluble in blood, because they don’t stay in the alveoli as long and are more readily drawn into the bloodstream. Conversely, lower cardiac output speeds induction because less blood is available to take up the anesthetic, allowing the alveolar concentration to rise more quickly. The oxygen content of the inspired gas isn’t the primary driver of this uptake rate.