Which factor primarily controls PaO2 levels?

The factor that primarily controls PaO2 levels is more accurately minute ventilation. Minute ventilation, which is the total volume of air ventilated per minute, plays a central role in determining the amount of oxygen that enters the alveoli and, consequently, the amount of oxygen available for diffusion into the bloodstream, impacting PaO2 levels.

While positive end-expiratory pressure (PEEP) does influence oxygenation, it mainly functions by preventing alveolar collapse at the end of expiration, thereby increasing functional residual capacity and improving lung recruitment. This can enhance ventilation-perfusion matching and increase PaO2 levels indirectly. However, it is not the primary determinant of PaO2; rather, it is a supportive strategy that may help maintain or improve oxygenation.

The respiratory rate and tidal volume also factor into gas exchange, as they influence minute ventilation; however, isolated changes in either of these parameters may not have as significant a direct impact on PaO2 as minute ventilation as a whole. Therefore, while the mechanisms of other options might contribute to the overall process of oxygenation, minute ventilation is the most critical factor in controlling PaO2 levels directly.