Etiology of dehydration:
Hypertonic dehydration
? (A) insufficient water intake
Coma patients or patients with mental disorders are not thirsty, do not know that drinking water and the amount of drinking water are insufficient, or oral and upper gastrointestinal diseases can not enter water or the water supply is cut off, such as in deserts and accidents. (2) The water demand of patients in high fever or high temperature environment increases, but it is insufficient. (C) excessive water loss
1. Vomiting, diarrhea, sticky and slippery intestines and gastrointestinal drainage lead to a large loss of digestive juice, instead of supplementing it.
2. Diabetes insipidus or renal tubules are insensitive to antidiuretic hormone (ADH), and a large amount of diluted urine is excreted to accept solute diuretics (mannitol, glycine, etc.). ) or osmotic diuresis caused by excessive intake of high protein and salty diet. Uncontrolled diabetic patients excrete a lot of glycosuria and renal concentration dysfunction, which leads to renal excretion more than sodium excretion.
? 3. Excessive sweating during high temperature and heavy physical labor.
4. Tracheotomy and hyperventilation can cause a lot of water loss in respiratory tract. The lost water is pure water. When the water intake is insufficient, it is easy to cause hypertonic dehydration.
Isoosmotic dehydration
1.Except for saliva, gastric juice and tympanic fluid secreted by colon, the contents of sodium in other secretions in the digestive tract are similar to those in plasma, so the diarrhea duodenum is decompressed. Thin tubes in digestive tract are also common causes of isotonic dehydration. Patients with hypertonic dehydration can also cause isotonic dehydration if only a small amount of water is supplemented.
2. A large number of pleural effusion ascites, or thoracic and abdominal drainage.
3. A large area of skin burn leads to a large amount of exudation.
4. Acute massive blood loss
Three-hypotonic dehydration
Low osmotic dehydration is common in hypertonic or isotonic dehydration, and only water is added but no salt is added, such as massive loss of digestive juice, application of diuretics, diabetes insipidus in polyuria stage of acute renal failure, diabetes and renal concentration dysfunction leading to massive urination, sweating, massive drainage of pleural and abdominal water, massive blood loss, etc.
Renal insufficiency and oliguria in acute renal insufficiency and chronic renal insufficiency, if the inflow of water is unrestricted due to the sharp decline of renal function, can lead to water accumulation in the body. In the case of severe heart failure or liver cirrhosis, renal drainage is also significantly reduced due to the reduction of effective circulating blood volume and renal blood flow. If the water load increases, water poisoning is easy to occur.
In the late stage of hypotonic dehydration, extracellular fluid is transferred to cells due to hypotonic extracellular fluid. It will cause intracellular edema, and when a large amount of water is input, it will cause water poisoning.
mechanism
No matter what kind of dehydration, they are dehydrated first, that is, the volume of extracellular fluid decreases. Extracellular fluid accounts for about 20% of the body weight of normal adults, while intracellular fluid accounts for 40% of the body weight. Extracellular fluid is divided into plasma (5% of body weight) and interstitial fluid (15% of body weight). Under normal circumstances, there is considerable difference in body fluid volume between different individuals, which is mainly determined by age, sex and obesity. The distribution of plasma interstitial fluid and intracellular fluid is relatively stable, and they are constantly exchanged. Plasma and tissue fluid are separated by a capillary wall, and all substances except protein can permeate freely, so the fluid balance on both sides of the capillary is mainly maintained by the hydrostatic pressure of colloid osmotic pressure and the capillary, that is, the blood pressure in the capillary. Interstitial fluid and intracellular fluid are separated by cell membrane. The cell membrane can permeate water and some small molecular solutes (such as urea). Colloids such as protein cannot pass through.
Diaosmotic dehydration
The body has been dehydrated, and the loss of sodium is greater than the loss of water. With the decrease of osmotic pressure of extracellular fluid, the reflex inhibition of antidiuretic hormone released from posterior pituitary weakens the reabsorption of water by distal renal tubules, so the urine volume in the early stage of hypotonic dehydration does not decrease, and the relative density of urine decreases. Because the osmotic pressure of extracellular fluid is lower than that of intracellular fluid, the water in extracellular fluid is also transferred to cells, which not only reduces the intracellular fluid, but also slightly increases it, while the extracellular fluid is obviously reduced. Because the extracellular fluid obviously reduces the appearance of dehydration symptoms, the symptoms of circulatory failure appear early and obviously. Due to the decrease of extracellular fluid volume, the increase of aldosterone secretion and late circulatory failure, renal blood flow is low. The decrease of glomerular filtration rate leads to the decrease of urine volume, the obvious decrease of sodium chloride content in urine, and azotemia's hypotonic dehydration. When the intracellular J solution is hypotonic, the dysfunction of the central nervous system can be caused by brain cell edema and late water poisoning, and there is no thirst symptom. ? ? Triisotonic dehydration
There are dehydrated water and steel in the human body, which are lost in proportion to normal body fluids, or hypertonic dehydration supplements a certain amount of water. Because it is isotonic dehydration, there is no influence of osmotic pressure. However, due to the lack of extracellular fluid volume, the reduction of effective circulating blood volume can also stimulate volume receptors, leading to the increase of ADH and aldosterone release, thus increasing the kidney's reabsorption of water needles, which is conducive to the maintenance of extracellular fluid volume. Generally speaking, a decrease in blood volume 10% will lead to an increase in ADHD release. Clinical patients showed decreased urine volume and urine sodium. Isoosmotic dehydration is the most common in clinical practice. If isotonic dehydration is not carried out, isotonic dehydration will be transformed into hypertonic dehydration due to the loss of water (such as water exhaled by the skin evaporation lung). Isoosmotic dehydration can be transformed into hypotonic dehydration if only water is added without sodium salt. If dehydration develops further, the volume of extracellular fluid will be significantly reduced, and besides the symptoms of dehydration on the body surface, blood pressure may drop, shock and even renal failure may occur.
According to the weight loss (water loss) and clinical manifestations, dehydration is divided into three degrees:
Mild dehydration and dehydration account for 2%-3% of body weight or 5% of weight loss, with only general neurological symptoms, such as headache, dizziness and weakness, and slightly decreased skin elasticity. Hypertonic dehydration with thirst
The body surface symptoms of moderate dehydration are obvious, with water loss accounting for 3%-6% of body weight, or 5%- 10%, and symptoms of circulatory insufficiency begin to appear.