The main components of body fluids are water and electrolytes. It is divided into two parts, cellular and extracellular fluids, the amount of which varies with sex, age and fatness. Adult male body fluid volume is generally 60% of body weight; adult female body fluid volume is about 55% of body weight. Children have less fat, so the proportion of body fluid to body weight is higher, in newborns, up to 80% of body weight. The amount of body fat increases with age, and after the age of 14, the proportion of body fluid in children is similar to that in adults. Disorders of fluid balance can cause disturbances in the body’s equilibrium. Differential diagnosis of fluid balance disorder: 1, isotonic dehydration: also known as acute or mixed dehydration. Surgical patients are most susceptible to this type of dehydration. Water and sodium are lost proportionally, serum sodium remains in the normal range, and the osmolality of the extracellular fluid remains normal. It results in a rapid decrease in extracellular fluid volume (including circulating blood volume). Stimulation of pressure receptors in the walls of small renal entry arterioles by the decrease in intratubular pressure and the decrease in Na+ in the distal tubular fluid due to the decrease in glomerular filtration rate causes excitation of the renin-aldosterone system and an increase in aldosterone secretion. Aldosterone promotes sodium reabsorption in the distal tubule, and there is an increase in the amount of water that is reabsorbed along with the sodium, causing extracellular fluid volume to rebound. Since the lost fluid is isotonic and essentially does not change the osmolality of the extracellular fluid, initially the intracellular fluid does not transfer to the extracellular space to compensate for the lack of extracellular fluid. Therefore, the amount of intracellular fluid does not change. However, after the loss of this fluid for a longer period of time, the intracellular fluid will also gradually move out, along with the loss of extracellular fluid, so as to cause cellular dehydration. 2, hypotonic water deficit: also known as chronic water deficit or secondary water deficit. Water and sodium deficiency at the same time, but less water than sodium loss, so the serum sodium is lower than the normal range, the extracellular fluid is hypotonic state. The body reduces the secretion of antidiuretic hormone, so that the reabsorption of water in the renal tubules is reduced, and the urinary output is increased to increase the osmotic pressure of extracellular fluid. However, the volume of extracellular fluid decreases even more, and the interstitial fluid enters the circulation, which partially compensates for the blood volume but makes the decrease in interstitial fluid more than the decrease in plasma. Faced with a marked reduction in circulating blood volume, the body will no longer be concerned with osmolality and will try to maintain blood volume. Excitation of the renin-aldosterone system causes the kidneys to decrease sodium excretion and increase reabsorption of CI- and water. Therefore, the urinary sodium chloride content is significantly reduced. Decreased blood volume in turn stimulates the posterior pituitary gland, causing increased secretion of antidiuretic hormone and increased water reabsorption, resulting in oliguria. If blood volume continues to decrease, shock will occur when the above compensatory function is no longer able to maintain blood volume. This kind of shock due to massive sodium loss is also called hyponatremic shock. Hypertonic water deficit: also known as primary water deficit. Although water and sodium are lacking at the same time, but the lack of water is more than the lack of sodium, so the serum sodium is higher than the normal range, and the extracellular fluid is hypertonic. The thirst center located in the lower part of the optic thalamus is stimulated by hypertonicity, and the patient feels thirsty and drinks water, so that the body water increases in order to reduce the osmotic pressure. On the other hand, hypertonicity of extracellular fluid can cause increased secretion of antidiuretic hormone so that water reabsorption by renal tubules increases and urine output decreases to lower the osmolality of the extracellular fluid and restore its volume. If water deprivation continues, increased aldosterone secretion caused by a significant decrease in circulating blood volume enhances reabsorption of sodium and water to maintain blood volume. In severe cases of water deprivation, the intracellular fluid moves to the extracellular space because of the increased osmotic pressure of the extracellular fluid, with the result that there is a decrease in both intracellular and extracellular fluid volumes. Eventually, the degree of intracellular fluid dehydration exceeds the degree of extracellular fluid dehydration. Brain cell dehydration will cause brain dysfunction. 4, too much water: also known as water intoxication or dilute hyponatremia. It means that the total amount of water entering the body exceeds the amount of water discharged, so that water is retained in the body, causing a decrease in the osmotic pressure of the blood and an increase in the amount of circulating blood. Water overload is less common. It is only in the case of excessive secretion of antidiuretic hormone or renal insufficiency, when the body takes in too much water or receives too many intravenous fluids, that water accumulates in the body, leading to water intoxication. At this time, the volume of extracellular fluid increases, serum sodium concentration decreases, and osmolality decreases. Because the osmotic pressure of the intracellular fluid is relatively high, water moves into the cells, resulting in a decrease in osmotic pressure and an increase in the volume of both intracellular and extracellular fluid. In addition, the increased volume of extracellular fluid inhibits aldosterone secretion, causing the distal tubules to reduce Na+ reabsorption and Na+ excretion from the urine to increase, resulting in an even lower serum sodium concentration. Dysregulation of fluid metabolism and acid-base balance is often a concomitant finding or consequence of a primary disease. Prompt measures should be taken to prevent the occurrence of such disorders. Generally, about 1500 ml of 5%-10% glucose solution, 500 ml of 5% grapefruit saline, and 130-40 ml of 10% KC can be injected intravenously daily to supplement the daily requirement of water and glucose, so as to economize the protein catabolism and to avoid the ketoacidosis that may occur when excessive fat burning occurs. For patients with fever, the amount of supplementation can generally be increased according to the criterion that for every 1C0 rise in body temperature, the loss of hypotonic body fluids from the skin is about 3 to 5 ml/kg. In patients with moderate sweating, the loss of body fluid is about 500-1000 ml (containing NaC 11.25-2.50 g); in cases of profuse sweating, the loss of body fluid is about 1,000-1,500 ml. In patients with tracheotomy, the daily evaporation of water from whistling is 2-3 times more than the normal one, counting 1,000 ml or so. All of them need to be increased in rehydration.