Hypertonic dehydration, also known as primary dehydration or hypernatremia with reduced extracellular fluid, is characterized by more water loss than sodium loss, a serum sodium concentration of 150 mmol/L, and a plasma osmolality of 310 mOsm/L. When there is more water deficiency than sodium deficiency, the osmolality of extracellular fluid increases, antidiuretic hormone secretion is increased, renal tubular reabsorption of water is increased, and urine output is decreased. Aldosterone secretion increases, and sodium and water reabsorption increases to maintain blood volume. If water deficiency continues, the osmolarity of extracellular fluid increases further, intracellular fluid moves to the extracellular, and eventually the degree of intracellular water deficiency exceeds the degree of extracellular fluid deficiency, which can eventually lead to brain cell dehydration which causes brain dysfunction. Causes of water loss more than sodium loss and high serum sodium concentration: I. Insufficient water intake: such as trauma, coma, esophageal disease, swallowing difficulties, inability to eat, insufficient water administration in critically ill patients, nasal feeding hypertonic diet or infusion of large amounts of hypertonic saline solution, etc. Mainly seen in the following cases: 1, can not or will not drink water such as oral, pharyngeal and esophageal disorders, patients with frequent vomiting, comatose patients or extremely debilitated patients, etc. 2, thirst disorders hypothalamic lesions can damage the thirst center, some patients with cerebrovascular accidents will also lose the sense of thirst. 3.The water source is cut off such as desert lost, sea wreck, etc. In the above cases, and through the skin and breathing of the constant insensible evaporation of water, causing more water loss than sodium loss, and the plasma osmotic pressure increases. Second, excessive water loss: not timely replenishment, such as high fever, massive sweating, large burns, tracheotomy, prolonged exposure of internal organs during thoracic and abdominal surgery, diabetic coma, etc. Including simple water loss and water loss more than sodium loss, that is, the loss of hypotonic fluids in two cases. 1.Simple water loss is through the skin, respiratory water loss and transrenal water loss. The former is seen in hyperthermia, hyperthyroidism and hyperventilation to enhance the amount of non-sensory evaporation, while the latter is seen in central uremia when ADH production and release are insufficient and in renal uremia when the kidney excretes a large amount of water due to the lack of response of the distal tubules and collecting ducts to ADH. Since such water loss occurs in the most distal part of the renal unit, in which the sodium ions have been mostly reabsorbed, the patient can excrete 10-15L of dilute urine containing only a few mmol of sodium per day. 2, more water loss than sodium loss, the first loss of digestive juices containing low sodium through the gastrointestinal tract, mainly seen in some infants and children with watery stool diarrhea, fecal sodium concentration of 60 mmol/L or less. The second is seen in the loss of hypotonic fluids during profuse sweating, which often occurs in hot environments. Also during repeated intravenous administration of hypertonic substances (such as mannitol, urea and hypertonic glucose), more water loss than sodium loss can occur due to osmotic diuresis caused by increased renal tubular fluid osmolarity. III. Other factors: Differences in the human body and other issues. Causes of hypertonic dehydration in children: There are many causes of dehydration in children, the most common being acute gastroenteritis and low fluid intake. Loss of body fluids due to vomiting and diarrhea is the cause of gastroenteritis and one of the most common causes of dehydration; another common cause of dehydration is low fluid intake, for example, difficulty swallowing due to oropharyngeal pain. Sometimes the formula is not mixed with water in the right ratio – too little water is added to the formula – which can also cause dehydration in infants.