Cardiogenic shock has the greatest impact on the rate of increase in FA/FI for which volatile anesthetic?

Cardiogenic shock has the greatest impact on the rate of increase in FA/FI for which volatile anesthetic?

• A. A Isoflurane
• B. B Desflurane
• C. C Sevoflurane
• D. D Nitrous oxide

Answer: (A)

The key idea is how fast the alveolar concentration of an inhaled anesthetic rises toward the inspired concentration, which depends on uptake into blood and tissues (driven by blood/gas solubility) and on pulmonary blood flow (cardiac output). In cardiogenic shock, the cardiac output is low, so less blood is delivered to the lungs to take up the agent. This reduction in uptake makes the alveolar concentration climb faster toward the inspired level, especially for agents that are highly soluble in blood. Isoflurane has the highest blood/gas solubility among the options, so its uptake into blood is greatest under normal conditions. When cardiac output falls, that uptake is curtailed, producing a larger relative change in the rate at which FA/FI increases for isoflurane than for the more soluble-desirable or less soluble agents. In contrast, agents with low blood solubility (like desflurane) show only a small change in FA/FI under reduced CO, so the impact of cardiogenic shock is less pronounced. Sevoflurane is intermediate in solubility, and nitrous oxide has relatively low solubility, so their FA/FI changes with shock are not as dramatic as that of isoflurane.

The key idea is how fast the alveolar concentration of an inhaled anesthetic rises toward the inspired concentration, which depends on uptake into blood and tissues (driven by blood/gas solubility) and on pulmonary blood flow (cardiac output). In cardiogenic shock, the cardiac output is low, so less blood is delivered to the lungs to take up the agent. This reduction in uptake makes the alveolar concentration climb faster toward the inspired level, especially for agents that are highly soluble in blood.

Isoflurane has the highest blood/gas solubility among the options, so its uptake into blood is greatest under normal conditions. When cardiac output falls, that uptake is curtailed, producing a larger relative change in the rate at which FA/FI increases for isoflurane than for the more soluble-desirable or less soluble agents. In contrast, agents with low blood solubility (like desflurane) show only a small change in FA/FI under reduced CO, so the impact of cardiogenic shock is less pronounced.

Sevoflurane is intermediate in solubility, and nitrous oxide has relatively low solubility, so their FA/FI changes with shock are not as dramatic as that of isoflurane.