Which option is NOT a noninvasive method to monitor oxygenation and ventilation?

• A. Arterial Blood Gas
• B. Pulse Oximetry
• C. Capnography
• D. Spirometry

Answer: (A)

The key idea is invasive versus noninvasive monitoring. An arterial blood gas requires drawing blood from an artery (or placing an arterial line), which is an invasive procedure. It gives precise measurements of oxygenation and ventilation (PaO2 and PaCO2) along with acid-base status, but the act of obtaining it involves breaking the skin and puncturing a vessel.

In contrast, pulse oximetry measures oxygen saturation through a sensor placed on a finger or earlobe and capnography monitors exhaled CO2 noninvasively, providing continuous information about ventilation. Spirometry is also noninvasive, using a mouthpiece to assess airflow and lung volumes, though it doesn’t directly monitor oxygenation or ventilation in real time.

So the item that is not a noninvasive method for monitoring oxygenation and ventilation is the arterial blood gas, because it requires arterial blood sampling.