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 level, and eventually the degree of intracellular water deficiency exceeds that of extracellular fluid deficiency, which can eventually lead to brain cell dehydration and cause brain dysfunction. Prevention of water loss more than sodium loss and high serum sodium concentration: 1.Master the pathogenesis of hypertonic dehydration and possible factors, clinical manifestations and laboratory test indexes, closely observe the changes of patient’s consciousness and skin mucosa, and be highly alert to the occurrence of hypertonic dehydration. 2. Collect blood specimens for examination in a correct and timely manner, and understand the laboratory results in a timely manner. Report to the doctor in time when abnormal laboratory indicators are found, especially when electrolyte indicators are close to abnormal although they are within the normal range. 3.Discover signs of hypertonic dehydration in time, such as when the patient has persistent hyperthermia and obvious dryness of skin and mucous membrane, take the initiative to contact the doctor and suggest checking electrolytes in order to confirm the diagnosis of hypertonic dehydration. 4.If the blood sodium and blood chloride are obviously increased and have reached moderate dehydration or above, the nurse should make a prompt decision to suspend the input of sodium and salt and promptly inform the doctor.