Hypertonic dehydration, also known as hypernatremia caused by primary dehydration or decreased extracellular fluid, is characterized by more water loss than sodium loss, serum sodium concentration > 150 mmol/L, and plasma osmotic pressure > 310 mosm/L.

1, reason and mechanism

(l) Insufficient drinking water: there are mainly the following situations: ① inability or inability to drink water, such as oral, pharyngeal and esophageal diseases, patients who often vomit, coma patients or extremely weak patients; Dystonia: Hypothalamic lesions can damage the thirst center, and some patients with cerebrovascular accidents will also lose their thirst; (3) Without water, such as getting lost in the desert or being shipwrecked. Under the above circumstances, water is evaporated through the constant insensitivity of skin and breathing, resulting in more water loss than sodium loss and increased plasma osmotic pressure.

(2) Excessive water loss: including simple water loss and more water loss than sodium loss, that is, the loss of hypotonic liquid. ① Simple dehydration includes percutaneous dehydration, respiratory dehydration and renal dehydration. The former is caused by high fever, hyperthyroidism and hyperventilation, while the latter is caused by insufficient production and release of ADH in central diabetes insipidus and insufficient response to ADH in renal diabetes insipidus, so the kidney excretes a lot of water. Because this dehydration occurs at the farthest end of nephron, most of the pro-sodium ions have been reabsorbed in this part, so patients can excrete 10 ~ 15L of diluted urine every day, which contains only a few millimoles of sodium. ② The loss of water is more than that of sodium. First, the digestive juice with low sodium content is lost through the gastrointestinal tract, which is mainly seen in some infants with watery diarrhea, and the fecal sodium concentration is below 60 mmol /L L ... Secondly, when sweating, low-permeability liquid is lost, which often happens in high temperature environment. In addition, when hypertonic substances (such as mannitol, urea and hypertonic glucose) are repeatedly injected intravenously, osmotic diuresis may lose more water than sodium due to the increase of osmotic pressure of renal tubular fluid.

2. Pathophysiological changes: water loss is more than sodium loss, which leads to the increase of osmotic pressure of extracellular fluid, which is a pathophysiological change caused by hypertonic dehydration.

(l) The increase of osmotic pressure of extracellular fluid stimulates thirst center, causing thirst and drinking water.

(2) The increase of osmotic pressure of extracellular fluid stimulates the osmotic pressure receptor of hypothalamic supraoptic nucleus, which increases the release of ADH and the reabsorption of water by renal tubules, resulting in the decrease of urine volume and the increase of urine specific gravity.

(3) The increase of osmotic pressure of extracellular fluid can make intracellular fluid water with relatively low osmotic pressure transfer to the outside of the cell.

It can be seen that during hypertonic dehydration, both intracellular fluid and extracellular fluid decrease, but the intracellular fluid mainly decreases and cell dehydration occurs, and extracellular fluid can be supplemented from the above three aspects, so the decrease of extracellular fluid and blood volume is not as obvious as that of hypotonic dehydration, and fewer people have circulatory disorders.