How would a right mainstem intubation affect the rate of increase in arterial partial pressure of volatile anesthetics?

How would a right mainstem intubation affect the rate of increase in arterial partial pressure of volatile anesthetics?

• A. It would be reduced to the same degree for all volatile anesthetics
• B. It would be accelerated to the same degree for all volatile anesthetics
• C. There would be no change if PaO2 is 60 mm Hg or greater
• D. It would be reduced the most for poorly soluble agents

Answer: (D)

Right mainstem intubation creates a significant ventilation–perfusion mismatch, effectively producing a shunt where blood bypasses gas-exchanging units. The speed at which arterial blood takes up a volatile anesthetic depends on how readily the agent moves from the alveoli into the blood, which is determined by the agent’s blood–gas solubility. When only one lung is ventilated, overall alveolar ventilation to exchange surfaces is reduced, so uptake into blood is constrained. This constraint has a greater impact on agents that are poorly soluble because they rely more on the available alveolar–capillary contact to return to the blood; with less surface area and fewer alveoli exchanging gas, their relatively small uptake capability becomes the limiting factor. Therefore, the rate of rise in arterial partial pressure would be reduced most for poorly soluble agents, making that choice the best fit.

Right mainstem intubation creates a significant ventilation–perfusion mismatch, effectively producing a shunt where blood bypasses gas-exchanging units. The speed at which arterial blood takes up a volatile anesthetic depends on how readily the agent moves from the alveoli into the blood, which is determined by the agent’s blood–gas solubility. When only one lung is ventilated, overall alveolar ventilation to exchange surfaces is reduced, so uptake into blood is constrained. This constraint has a greater impact on agents that are poorly soluble because they rely more on the available alveolar–capillary contact to return to the blood; with less surface area and fewer alveoli exchanging gas, their relatively small uptake capability becomes the limiting factor. Therefore, the rate of rise in arterial partial pressure would be reduced most for poorly soluble agents, making that choice the best fit.