TYK138
Which of the following best describes the relationship between cardiac output and speed of induction in infants?
a) Infants have a decreased cardiac output compared to adults, and thus an increased induction speed.
b) Infants have an increased cardiac output compared to adults; this explains the observed increase in induction speed.
c) Infants have similar cardiac output (per kilogram); this is unrelated to induction speed.
d) Infants have faster induction speeds despite having increased cardiac output.
Answer
Answer d.
Normally the speed of an inhalational induction is inversely related to cardiac output (CO); that is, it is increased with a low cardiac output and slowed down by a higher CO. This is counterintuitive, as one would think that with a low CO the pick-up of volatile anesthetic would be slower. However, low CO means that the blood returning to the heart is coming back with more vapor in it (which raises the FA/FI ratio). In infants, the Vessel Rich Group receives a much higher percentage of CO (18% vs. 8%); thus, the blood returning to the heart rapidly equilibrates and comes back at higher concentrations, raising the FA/FI similarly to the mechanism described above for low CO.
Notes
- This question originally printed in the Pediatric Anesthesiology Review Topics kindle book series, and appears courtesy of Naerthwyn Press, LLC.
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