Which of the following is a sign of hypoxia?

Hypoxia refers to a condition where there is a deficiency in the amount of oxygen reaching the tissues. One of the most recognizable signs of hypoxia is the presence of cyanosis, which is characterized by a blue or gray discoloration of the skin. This occurs because, as oxygen levels drop, the blood is unable to carry sufficient oxygen to surrounding tissues. The bluish hue typically first appears in areas with less blood flow, such as the lips, face, or extremities, and it signals a serious deficiency of oxygen that requires immediate medical attention.

Other physiological responses, such as high blood pressure, rapid heart rate, and cold extremities, can be associated with various medical conditions, but they are not definitive indicators of hypoxia. High blood pressure may occur due to a stress response rather than a lack of oxygen, rapid heart rate can be a compensatory mechanism from various causes, and cold extremities may reflect poor circulation or other issues unrelated to oxygen levels. Thus, the blue or gray skin directly indicates insufficient oxygen in the blood, distinguishing it as a clear sign of hypoxia.