Which of the following is an indicator of hypoxemia?

The presence of a blue tint to the lips or face, known as cyanosis, is a strong indicator of hypoxemia, which is a deficiency of oxygen in the blood. Cyanosis occurs when blood oxygen levels drop significantly and the hemoglobin in the blood is deoxygenated, causing a bluish color to superficial tissues, particularly in areas with thin skin like the lips and face. This physiological response is a critical sign that can help healthcare professionals quickly assess the oxygenation status of a patient.

Skin rash, sudden fatigue, and excessive sweating can be symptoms of various conditions, but they are not direct indicators of hypoxemia. While sudden fatigue may be associated with low oxygen levels, it is not specific enough to be considered a definitive sign. Similarly, skin rash and excessive sweating can result from many other health issues and do not specifically indicate low oxygen saturation in the blood. Therefore, the blue tint to lips or face is the most direct and visible indicator of hypoxemia, making it the correct answer.