Which specialty gas is utilized for determining FRC with a nitrogen washout test?

The nitrogen washout test is designed to assess functional residual capacity (FRC) by measuring the amount of nitrogen present in the exhaled air after inhaling a gas mixture. In this test, the patient breathes in a gas that should rapidly replace the nitrogen in their lungs. The correct specialty gas used for this procedure is oxygen.

When a patient inhales a pure oxygen gas mixture, the nitrogen that is normally present in the lungs gets washed out. This is because oxygen is well absorbed into the bloodstream while nitrogen remains in the lungs and is exhaled. The measured concentrations of nitrogen in the exhaled air can then be used to calculate the FRC based on the initial nitrogen levels when the patient was breathing room air.

Using other gases, such as helium, carbon dioxide, or nitrous oxide, would not effectively accomplish this goal in the context of a nitrogen washout test. Helium is commonly used in other tests, such as the helium dilution method for lung volume measurements, but it does not achieve the same nitrogen washout effect. Understanding the role of oxygen in this specific test is key in pulmonary function testing, as it highlights the principles involved in measuring lung volumes and capacities accurately.