The loss of body fluids resulting in a decrease in extracellular fluid is called dehydration. When people work in high temperature conditions, strenuous exercise or certain diseases (such as violent vomiting, severe diarrhea), they will lose a lot of water and inorganic salts (mainly sodium), which will lead to a decrease in the body’s extracellular fluid osmotic pressure and symptoms such as a drop in blood pressure, increased heart rate, four chills, and even coma in severe cases. Prevention of extracellular fluid reduction: 1. The choice of drinks differs according to the situation. High concentration juice or other high concentration fluids (chocolate drinks, cereals, etc.) should not be used instead of drinking water during strenuous exercise. Recommended drinks: hot water, tea, low-concentration fruit juice, vit.c effervescent drinks or other sports drinks. 2, at the same time need to eat appropriate salty nuts or road food, can replenish the loss of salt in the body. Carry 1l~2l thermos bottle during the march. 3.Drink more water. Drink more hot tea when the camp activity can prevent dehydration, but also can keep warm. Drink a glass of water before leaving for marching activities, and drink moderate amount of water (equal amount of drinks) once every 30 minutes on the way. Daily water intake > 2000ml/d (camp activities) ~ 3000ml/d (when marching). 4, the journey of water must be distributed reasonably, the water to and from the water should have a good falsehood, fully consider the return trip drinking water and the response to unexpected situations. Avoid eating snow and ice to prevent frostbite in the mouth and throat. (7) Quit smoking, avoid alcohol, and reduce the intake of spicy and high-salt food.