Heat syncope: definition

Heat syncope is a brief loss of consciousness or near-faint caused by heat-related blood pooling and reduced brain blood flow. It often occurs after standing in a hot environment, especially when sweating or tired.

Heat makes blood vessels near the skin widen so the body can release warmth. Standing can then allow blood to collect in the legs, briefly reducing the blood reaching the brain. Light-headedness, blurred vision, nausea, weakness, and a pale appearance may come before the faint.

Guide the person to the floor before they fall, place them on their back, and raise their legs if safe. Move them to a cooler area and loosen clothing. Once fully alert, they can take slow sips of fluid. Have them sit before standing and avoid more heat until recovered.

Call emergency services for breathing difficulty, chest pain, seizure, serious injury, prolonged confusion, or failure to wake. Seek clinical review for a first faint, repeated fainting, an episode during exertion, or an event without heat or posture as an obvious trigger.

Ask how to distinguish heat syncope from dehydration, low blood sugar, anaemia, or an abnormal heart rhythm, and whether you need tests.