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 and cause brain dysfunction. More water loss than sodium loss and high serum sodium concentration need to do the following tests: 1, urine specific gravity (SG), that is, urine specific gravity, is the ratio of urine to the weight of the same volume of pure water at 4 degrees Celsius. Because urine contains 3-5% solids, the urine specific gravity is greater than pure water. The urine specific gravity varies with the water, salt and organic content in the urine in pathological cases also affected by protein, urine sugar and cellular components, etc. If there is no water metabolism disorder, urine specific gravity measurement can roughly reflect the concentration and dilution function of the renal tubules. This test is suitable for people with kidney disease, dehydration or water excess, and when abnormal excretion of substances is suspected. 2.Serum sodium Sodium in the body is mainly derived from salt in food and absorbed into the blood through the intestine, of which 47% is present in the bones. About 10% exists in the intracellular fluid and 44% in the extracellular fluid. It is the most abundant cation in the extracellular fluid, mostly in the form of sodium chloride, and 95% of the sodium in the body is excreted through the kidneys. The main function of sodium is to maintain the volume of extracellular fluid, maintain osmotic pressure and acid-base balance, and has the role of maintaining normal stress in muscles and nerves. 3, red blood cell count The red blood cell count, the number of red blood cells contained in a unit volume of blood, is important for suggesting diseases involving the red blood cell system. Under normal circumstances, the production and destruction of red blood cells are in dynamic balance, so the quantity and quality of red blood cells in the blood remains relatively stable. Whatever the cause of the malfunction of red blood cell production and destruction, it will cause changes in the quantity or quality of red blood cells, thus leading to the occurrence of disease. 4.Hemoglobin Hemoglobin is the main component of red blood cells. Each hemoglobin molecule is composed of four heme groups with beads of protein, and each heme is composed of four pyrrole rings with an iron atom in the center of the ring. Iron in hemoglobin in the divalent state can be reversibly bound to oxygen (oxyhemoglobin), if iron is oxidized to the trivalent state. The hemoglobin then transforms into methemoglobin and loses its oxygen-carrying capacity. There are four methods used to determine hemoglobin content: ① Colorimetric method: This is the most widely used method in clinical practice, which can be divided into two categories: visual colorimetry and photoelectric colorimetry, the latter of which is further divided into cyanide methemoglobin method, alkaline hemoglobin method, acidified hemoglobin and oxyhemoglobin method according to the different dilutions used. A good diluent must be able to convert all the hemoglobin in the blood into a stable hemoglobin derivative so that the total amount of hemoglobin in the blood can be measured. The cyanogenic methemoglobin method essentially has this advantage, as it converts all hemoglobins except sulfated hemoglobin (which is rare in normal human blood) into stable cyanogenic methemoglobin. Therefore, the results measured by this method are accurate and reproducible. Therefore, the cyanide methemoglobin method has become the international standard method for determining hemoglobin. The visual colorimetric method of hemoglobin has been eliminated abroad because of its poor accuracy. However, the method is simple and economical, and is still used in some primary care units. ②Iron measurement method. ③ oxygen measurement method: these two methods are complex, not suitable for routine use. ④ specific gravity method: the accuracy of the method is poor. 5, serum chloride refers to the concentration of chloride ions in the serum. Chlorine is the main anion in human extracellular fluid, plays an important role in regulating the body’s acid-base balance, osmotic pressure and water distribution. Serum chloride (Cl-,Cl) test can understand the concentration of chloride ions in the serum. Increase is seen in renal insufficiency due to acute and chronic glomerulonephritis, urinary tract obstruction, respiratory alkalosis, excessive chloride intake, and hypertonic dehydration. Decrease is seen in large loss of fluid from the gastrointestinal tract, vomiting, gastrostomy, acute renal insufficiency, etc.