How long would a vaporizer containing 150 mL of isoflurane deliver a 2% concentration at a total fresh gas flow of 4 L/min?

How long would a vaporizer containing 150 mL of isoflurane deliver a 2% concentration at a total fresh gas flow of 4 L/min?

• A. 2 hours
• B. 4 hours
• C. 6 hours
• D. 8 hours

Answer: (C)

The amount of liquid isoflurane that a vaporizer can deliver over time depends on how fast it evaporates to maintain the set concentration at the given fresh gas flow. A practical way to estimate this rate is to multiply the flow by the concentration (as a decimal) and by a conversion factor that reflects how much liquid is needed to produce the vapor at that flow and setting. Using a commonly taught approximation: liquid consumption rate ≈ flow (L/min) × concentration × 5 (mL/min). With a total flow of 4 L/min and a setting of 2%, the consumption rate is about 4 × 0.02 × 5 = 0.4 mL/min. A 150 mL reservoir would thus last roughly 150 ÷ 0.4 ≈ 375 minutes, which is about 6 hours. So, at these conditions, the vaporizer would deliver isoflurane for around six hours. If you changed the flow or the concentration, the duration would change in the same proportional way: higher flow or higher concentration would shorten the time; lower values would extend it.

The amount of liquid isoflurane that a vaporizer can deliver over time depends on how fast it evaporates to maintain the set concentration at the given fresh gas flow. A practical way to estimate this rate is to multiply the flow by the concentration (as a decimal) and by a conversion factor that reflects how much liquid is needed to produce the vapor at that flow and setting. Using a commonly taught approximation: liquid consumption rate ≈ flow (L/min) × concentration × 5 (mL/min). With a total flow of 4 L/min and a setting of 2%, the consumption rate is about 4 × 0.02 × 5 = 0.4 mL/min. A 150 mL reservoir would thus last roughly 150 ÷ 0.4 ≈ 375 minutes, which is about 6 hours. So, at these conditions, the vaporizer would deliver isoflurane for around six hours. If you changed the flow or the concentration, the duration would change in the same proportional way: higher flow or higher concentration would shorten the time; lower values would extend it.