Which symptom is indicative of hypoxia?

Cyanosis is a symptom that indicates hypoxia, which is a deficiency of oxygen in the tissues. When the body tissues do not receive sufficient oxygen, it can lead to a bluish discoloration of the skin and mucous membranes, particularly in areas with thin skin such as the lips, fingertips, and toes. This bluish tint occurs because deoxygenated hemoglobin in the blood has a different absorption spectrum than oxygenated hemoglobin, making it visible.

The other symptoms listed—high fever, fatigue, and excessive thirst—are not specific indicators of hypoxia. High fever is typically associated with infections and inflammation, fatigue can result from a variety of conditions including anemia and chronic illness, and excessive thirst often relates to dehydration or diabetes. While these symptoms can occur in conjunction with hypoxia, they do not serve as definitive signs of inadequate oxygenation in the body.