Extremely low urinary sodium excretion is the prominent clinical manifestation of hyponatremia. The normal value of blood sodium is 142 mmol/L (135-145 mmol/L), and blood sodium below 135 mmol/L is hyponatremia. Urinary sodium: 70-90 mmol/24h in normal adults, which is about 4.1-5.3 g of sodium chloride. if urinary Na+. The following diseases are also causes of very low urinary sodium excretion: 1, pediatric congestive heart failure Congestive heart failure is referred to as heart failure. Heart failure is a cardiac dysfunction in which the reduced cardiac output cannot meet the needs of the body. Clinically, heart failure is a syndrome consisting of four parts: cardiac dysfunction, reduced exercise tolerance, pulmonary circulation congestion, and arrhythmia in the late stage. Cardiac dysfunction is necessary to constitute heart failure, and the other three components are clinical manifestations of the compensatory mechanisms of cardiac insufficiency. Early by accelerating the heart rate, myocardial hypertrophy and cardiac enlargement and other compensation, when the volume of blood excretion to meet the needs of the body only cardiac dysfunction, there are no signs of heart failure, called cardiac function compensation period. During this period, the progress of the disease is the emergence of the pulmonary circulation and / or corporal circulation stasis, the child’s shortness of breath, shallow, cough and perioral bruising, jugular veins, jugular veins, liver and spleen enlargement, edema. Congestive heart failure is the clinical manifestation. Heart failure is a serious health hazard for children, and is a common pediatric emergency that should be rescued in a timely manner. 2, diarrhea normal people usually defecate once a day, individual daily defecation 2 ~ 3 times or once every 2 ~ 3 days, the normal nature of feces, the average weight of feces discharged per day is 150 ~ 200g, containing 60% to 75% of water. Diarrhea (diarrhea) is a common symptom, refers to the number of bowel movements significantly more often than usual, thin fecal matter, increased moisture, the amount of feces per day more than 200g, or contain undigested food or pus, blood, mucus, diarrhea is often accompanied by a sense of urgency to defecate, anal discomfort, incontinence and other symptoms, diarrhea is divided into two categories of acute and chronic. Acute diarrhea onset of acute, within 2 to 3 weeks, chronic diarrhea refers to the duration of the disease in more than two months or intervals within 2 to 4 weeks of recurrent diarrhea. Diarrhea is a common symptom of digestive system diseases, which refers to more frequent than usual bowel movements, loose stools with increased water content, sometimes with increased fat, with non-digestible substances, or mixed with pus and blood mucus. Normal people usually defecate once a day, a few people defecate 2-3 times a day or once every 2-3 days, and the feces are formed, normal, should not be called diarrhea. Diarrhea is often accompanied by urge to defecate, perianal discomfort, incontinence and other symptoms. Diarrhea is divided into acute and chronic two kinds of diarrhea, diarrhea in the course of more than 2 months, or intervals in 2 ~ 4 weeks of recurrent diarrhea called chronic diarrhea. Cirrhosis Cirrhosis is a common chronic progressive liver disease, which is a diffuse liver damage formed by one or more etiologic factors over a long period of time or repeatedly. In China, most of them are post hepatitis cirrhosis, and a few of them are alcoholic cirrhosis and schistosomal cirrhosis. Pathohistologically, there are extensive hepatocellular necrosis, nodular regeneration of residual hepatocytes, proliferation of connective tissue and formation of fibrous septa, leading to destruction of hepatic lobular structure and pseudo lobe formation, and the liver gradually deforms and hardens and develops into cirrhosis. Early stage of cirrhosis may have no obvious symptoms due to the strong compensatory function of the liver, but later stage of cirrhosis is mainly characterized by liver function impairment and portal hypertension, with multi-systemic involvement, and in the late stage of cirrhosis, complications such as upper gastrointestinal hemorrhage, hepatic encephalopathy, secondary infections, splenomegaly, ascites, and carcinoma are often seen. Cirrhosis is distributed all over the world, regardless of nationality and ethnicity, seriously jeopardizing people’s health. There are no accurate statistics on the incidence of cirrhosis. According to the figures provided by the World Health Organization (WHO) in 1987, the average incidence rate of cirrhosis in the population is about 17.1 per 100,000 people. According to the figures provided by 55 countries to WHO, the number of people who die of cirrhosis in the world each year exceeds 310,000 and has increased to 500,000 in recent years. In Western Europe and the United States, the number of deaths due to liver cirrhosis is the fifth leading cause of death after malignant tumors, cardiovascular diseases, cerebrovascular diseases and accidents. Among middle-aged people in the United States, it is the fourth leading cause of death. The incidence of cirrhosis varies greatly from country to country and from region to region in the same country. Alcoholic cirrhosis is the main cause of cirrhosis in developed countries in the West, accounting for more than 2/3 of all cirrhosis. The increase in the number of alcoholics is the main reason for the rising incidence of cirrhosis in these countries in recent years. The incidence of cirrhosis increases with alcohol consumption. For example, the incidence of alcoholic cirrhosis in France is 300/100,000 population, and is three times higher in men than in women. If alcohol consumption is greater than 40-50g/d, the incidence rate increases to 2500/100,000 people. In Birmingham, England, the incidence rate in 1960 was 5.6,/100,000 population; in 1974, it reached 153/100,000 population. In France, the age-standardized morbidity and mortality rate was 10/100,000 population in 1945, and in 1967 it rose to 40/100,000 population. China’s incidence of cirrhosis accounted for about 1% of the total number of hospitalized patients in the same period, with hepatitis virus infection resulting in posthepatitis cirrhosis as the most common. But in recent years, the incidence of alcoholic cirrhosis increased significantly. 4, tropical stomatitis diarrhea tropical stomatitis diarrhea (tropical sprue) occurs in the tropical residents in South America, Africa, India and other Southeast Asian countries are the most common, any age can suffer. In recent years, this disease in the tropics has been categorized in the “infectious malabsorption” type, and the disease is divided into parasitic (i.e. giardia) and non-parasitic (tropical stomatitis diarrhea) two kinds. 5.Malnutritional cirrhosis Malnutritional cirrhosis is caused by long-term nutritional deficiency. The causes of malnutrition, in addition to individual patients due to insufficient intake, most of them are due to other diseases limiting food intake and absorption, such as after small bowel bypass surgery, Birroth Ⅱ type of postoperative, and so on. 6, hypotonic dehydration Hypotonic dehydration refers to water and sodium deficiency at the same time, but the lack of water is less than the lack of sodium, 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 urine output increases to increase the osmolality of the extracellular fluid. However, the volume of extracellular fluid is in turn more reduced. Intertissue fluid enters the blood-blood circulation, which partially compensates for blood volume but makes the decrease in intertissue fluid more than the decrease in plasma. Faced with a marked reduction in circulating blood volume, the body will no longer take osmolarity into account and try to maintain blood volume. Excitation of the renin-aldosterone system causes the kidney to decrease sodium excretion and increase reabsorption of Cl- and water. Therefore, the urinary sodium chloride content is significantly reduced. Decrease in blood volume in turn stimulates the posterior pituitary gland, causing increased secretion of antidiuretic hormone and increased water reabsorption, resulting in oliguria. If the decrease in blood volume will continue to decrease, shock will occur when the above compensatory function is no longer able to maintain blood volume. This kind of shock caused by massive sodium loss is also called hyponatremic shock.