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 the dehydration continues, the osmolarity of extracellular fluid increases further, intracellular fluid moves to the extracellular, and eventually the degree of intracellular dehydration exceeds the degree of extracellular fluid dehydration, which can eventually lead to brain cell dehydration which causes brain dysfunction. Classification of hypertonic dehydration: 1. Mild dehydration: Due to the reduction of water in the body, the child will feel slightly thirsty and have urine excretion, and the examination will show that the child is generally in good condition, the two eye sockets are slightly sunken, and the skin of the abdomen or inner thighs retracts quickly after pinching. 2.Moderate dehydration: the child is irritable, easily irritated, thirsty for water, the baby looks around for a nipple, if it gets a bottle, it will suck desperately, cry with fewer tears, the amount and number of urine is also reduced, the examination shows that the child’s two eye sockets are sunken, the mouth and tongue are dry, and the skin on the abdominal wall and inner thighs retracts slowly after pinching up. 3.Severe dehydration: The child is now extremely shrunken, lethargic, or even comatose, with very serious mouth drinking, no tears flowing out when crying, and the volume and number of urine is obviously low. On examination, the child’s eyes were clearly sunken, his mouth and tongue were very dry, and the skin on the abdominal wall and inner thighs retracted very slowly after pinching. Differential diagnosis of high serum sodium concentration and more water loss than sodium loss: Hypotonicdehydration: Also known as secondary dehydration or hyponatremia with reduced extracellular fluid, characterized by more sodium loss than water loss, serum sodium concentration of 135 mmol/L and plasma osmolality of 280 mOsm/L. Isotonicdehydration isotonicdehydration): Also known as mixed dehydration or reduced extracellular fluid with normal blood sodium concentration. It is characterized by a proportional loss of water and sodium, with a serum sodium concentration of 130-150 mmol/I and a plasma osmolality of 280-310 mOsm/L.