What is the approximate PaO2 when SaO2 is 50%?

When interpreting the relationship between arterial oxygen partial pressure (PaO2) and oxygen saturation (SaO2), it is essential to understand the principles of the oxygen-hemoglobin dissociation curve. At an SaO2 of approximately 50%, the PaO2 is generally about 26-27 mmHg.

This value reflects the significant drop in oxygen saturation as the partial pressure of oxygen decreases. The curve is sigmoidal in shape, meaning that at lower levels of PaO2, small changes in pressure lead to larger changes in SaO2. At around 50% saturation, the PaO2 is typically close to this range due to the steep portion of the dissociation curve, indicating that hemoglobin is only partially saturated with oxygen.

By using this understanding of the oxygen-hemoglobin dissociation curve, the corresponding PaO2 for an SaO2 of 50% is clearly established around 26-27 mmHg, making this the correct answer.