dehydration

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synonym water loss (dehydration) generally refers to dehydration (symptoms)

Dehydration is a symptom of metabolic disorder caused by the fact that the human body consumes a large amount of water due to pathological changes and cannot be replenished immediately Collapse , even life-threatening, and it needs to rely on infusion to supplement body fluids.

Chinese name: dehydration
Foreign name: dewatering

Nature: symptom
Classification: Low permeability dehydration Hypertonic dehydration

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Dehydration often occurs in severe vomiting, diarrhea, sweating and bleeding.

Dehydration Overview

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dehydration

finger Extracellular fluid A group of clinical symptoms caused by reduction Syndrome According to the accompanying changes in blood sodium or osmotic pressure, dehydration can be divided into hypotonic dehydration, that is, extracellular fluid reduction combined with hyponatremia; Hypertonic dehydration That is, extracellular fluid decrease and hypernatremia; Isotonic dehydration means that extracellular fluid is reduced and blood sodium is normal. Causes of dehydration:

I Hypertonic dehydration

（1） Insufficient water intake

Coma patients or insane The patient has no thirst and does not want to drink water, and the water intake is insufficient, or the oral cavity digestive tract The lesion cannot enter water or the water source is cut off, as in desert And no water in accidents.

（2） Increased water demand

High fever Patient or in high temperature environment water demand Increased but insufficient.

（3） Excessive water loss

1. Vomiting, diarrhea, thin intestines, and gastrointestinal drainage cause a large amount of digestive fluid loss and can not be supplemented

2． Diabetes insipidus Or renal tubule pair Antidiuretic hormone (ADH) Not sensitive, but excretes a large amount of diluted urine to receive solute diuretic （ mannitol 、 glycine Etc.) or high protein Caused by excessive intake of salt diet Osmotic diuresis , Uncontrolled diabetes The patient excreted a large amount of diabetes and renal concentration dysfunction, which led to the kidney draining more than sodium.

dehydration

3. High temperature and weight physical labor A lot of sweat when

4． Tracheotomy and Hyperventilation It can make water from respiratory tract A large amount of lost water is pure water, which is easy to be caused when water intake is insufficient Hypertonic dehydration 。

2、 Isotonic dehydration

1． digestive tract The liquid in the digestive tract contains less sodium except saliva, gastric juice and tympanic fluid secreted by the colon Secretory fluid The content of sodium is similar to that of plasma, so diarrhea duodenum Decompression. The thin tubes of digestive tract are also Isotonic dehydration Common causes. Hypertonic dehydration Only a small amount of water supplementation can also cause Isotonic dehydration

2. Massive pumping Hydrothorax Ascites, or thoracic and abdominal drainage

3. Large area of skin burn Cause a lot of seepage

4. Acute massive blood loss

3、 Hypotonic dehydration

dehydration

Hypotonic dehydration Common in hypertonic or Isotonic dehydration Time only Make up water There is no salt supplement, such as the loss of digestive juice, the use of diuretics acute renal failure Polyuria Diabetes insipidus 、 diabetes And kidney concentration dysfunction, which leads to the discharge of a large amount of urine, a large amount of sweating, a large amount of chest drainage ascites , such as massive blood loss, the drainage function of the four kidneys is insufficient in an emergency Chronic renal insufficiency Oliguria , because the drainage function of the kidney decreases sharply, if the water inflow is not limited, it can cause water retention in the body; serious heart failure or cirrhosis Due to Effective circulating blood volume and Renal blood flow If the water load is increased, it is easy to cause Water poisoning 。

Hypotonic dehydration In the late stage, due to the low permeability of extracellular fluid, Extracellular fluid Intracellular metastasis. Can cause Intracellular edema If a large amount of water is input Water poisoning 。

mechanism

dehydration

No matter what type of dehydration, they all have dehydration at first, that is, there are Extracellular fluid Capacity reduction. Extracellular fluid About 20% of the body weight of normal adults and 40% of the body weight. Extracellular fluid It is also divided into plasma (5% of body weight) and Interstitial fluid (15% of body weight) Part II. Under normal circumstances, there are considerable differences in body fluid volume between different individuals, which mainly depends on age, sex and obesity. The distribution of plasma interstitial fluid and intracellular fluid is relatively stable, and they are constantly exchanged. There is a layer between plasma and interstitial fluid Capillary wall Materials other than protein can be freely permeable, so blood capillary Bilateral Liquid balance Mainly by Colloid osmotic pressure And the hydrostatic pressure of capillaries, that is, the blood pressure in capillaries. Between interstitial fluid and intracellular fluid cell membrane Separate cell membrane from water and some Small molecule Solute (e.g urea ）It can be transparent, protein Colloids such as sodium and potassium cannot pass through, although electrolytes such as sodium and potassium can Entrance and exit cell , but it is subject to Sodium pump (The cell membrane is not loud, and the blood pressure is generally not low Hypertonic dehydration If the cause of dehydration continues to exist and dehydration continues to worsen to moderate dehydration (weight loss of more than 4%), the increase of aldosterone secretion is to regulate blood volume and Extracellular fluid Volume is an important hormone. Hypertonic dehydration Further development, blood volume cannot be maintained, and blood pressure falls to the bed Circulatory failure Symptoms and signs of. In case of severe dehydration, the water evaporated from the skin will be reduced Thermoregulation Affected, so the temperature rises, which is clinically called Dehydration heat Due to the transfer of intracellular water to Extracellular fluid Therefore, cell dehydration is more obvious clinically Brain cell Dehydration, and the center caused by it Nerve dysfunction In addition, due to dehydration of cells Metabolic disorder ， Catabolism Strengthened and incompletely oxidized metabolites are discharged from the kidney and reduced, which may occur Azotemia 。 Hypertonic dehydration Hour Serum sodium The concentration must increase.

Osmotic dehydration

The body is dehydrated and sodium loss is greater than water loss. because Extracellular fluid The decrease of osmotic pressure will reflexively inhibit the release of antidiuretic hormone from the posterior pituitary Renal tubule The reabsorption of water is weakened, so Hypotonic dehydration Early stage of Urine output No decrease, and urine relative density Decrease due to Extracellular fluid The osmotic pressure of the extracellular fluid is lower than that of the intracellular fluid, so the water in the extracellular fluid is also transferred into the cells, so that the intracellular fluid is not only not reduced but sometimes slightly increased, while the extracellular fluid is significantly reduced. Because the extracellular fluid is significantly reduced, the body surface symptoms of dehydration appear early and obvious, and the symptoms of circulatory failure appear early and obvious. because Extracellular fluid Volume decrease, aldosterone secretion increase, and late circulatory failure, Renal blood flow Less; Glomerular filtration rate Decreased urine volume sodium chloride The content is significantly reduced, and Azotemia Hypotonic dehydration The intracellular J fluid is hypotonic, so there is no thirst symptom. In the late stage, brain cell edema may also occur Water poisoning And cause dysfunction of central nervous system.

Isotonic dehydration

dehydration

Dehydrated water and steel in the body are lost in proportion to normal body fluid, or Hypertonic dehydration A certain amount of water was added. Because is Isotonic dehydration There is no influence of osmotic pressure factor, but due to Extracellular fluid Insufficient capacity, Effective circulating blood volume Reduce and stimulate Volume receptor It can increase the release of ADH and aldosterone, increase the reabsorption of water pins by the kidney, and is conducive to the maintenance of extracellular fluid volume. In general, the decrease of blood volume up to 10% can cause the increase of ADH release. Clinical patients showed decreased urine volume and decreased urine sodium in clinical practice Isotonic dehydration Most common. Isotonic dehydration If untreated, the isotonic may change into Hypertonic dehydration Small If only water is added but no sodium salt is added, it can be converted into Hypotonic dehydration If dehydration develops further, Extracellular fluid The volume is significantly reduced. In addition to the signs of dehydration on the body surface, blood pressure can also drop, shock and even renal failure Etc. According to weight loss (water loss) and clinical manifestations, dehydration is divided into three degrees:

l． Mild dehydration The amount of water loss accounts for 2% - 3% of body weight or 5% of body weight loss. There are only general neurological symptoms, such as headache 、 Dizziness and weakness, skin elasticity slightly reduced. Hypertonic dehydration Be thirsty

2． Moderate dehydration Dehydration, which accounts for 3% - 6% of body weight or 5% - 10% of body weight loss, has become apparent on the body surface, and circulatory dysfunction begins to appear.

3. Severe dehydration and water loss account for more than 6% of body weight or more than 10% of body weight loss. The above symptoms and signs become worse, and even shock and coma occur.

Western Medicine · Dehydration

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[Disease name (English)]: dehydration

[Pinyin]: TUOSHUI

dehydration

Western medicine Disease classification 】Metabolic and nutritional diseases [Western medicine definition]: Dehydration refers to the human body Internal water Minute Output Various physiological or Pathological state 。 Normal adults generally enter the same (balanced) state of water and output the same water within a unit time (such as 1d), so the total amount of water in the body is very stable, accounting for about 55% - 60% of the body weight. The amount of water entering includes drinking water and food water content And the water generated by the oxidation of sugar and fat in the body, about 2000-3000ml per day. The output water volume includes urine volume, skin and respiratory tract under unconsciousness (i.e. no obvious sweating and Shortness of breath The amount of water discharged and the amount of water in feces is 2000-3000ml per day.

[Western medicine etiology]: When the human body is in the High temperature environment , or excessive sweating after exercise may cause water loss, or High fever , various Hypermetabolism Status (e.g Hyperthyroidism Etc.), or due to anorexia, oral cavity esophagus Can't eat or drink, or because of vomiting, diarrhea Gastrointestinal decompression , alimentary canal fistula , or due to diuresis kidney trouble Polyuria , or due to Posterior pituitary secretion Antidiuretic hormone Insufficient and polyuria can cause dehydration. Shortness of breath can also cause respiratory tract Dehydration.

[Symptoms] Signs Dehydration is often accompanied by sodium loss electrolyte lose. When dehydration is greater than sodium loss, it can cause plasma and Extracellular fluid Occurs due to concentration Hypertonic dehydration I.e Plasma osmolality greater than Normal high Limit (about 300mmol/L). For example, dehydration/sodium loss ratio and plasma (such as Intestinal fluid ）When similar, it will cause Isotonic dehydration That is, although dehydrated, Plasma osmolality Keep normal. If dehydration is less than sodium loss Hypotonic dehydration , then Plasma osmolality It is lower than the normal lower limit (about 270mmol/L). However, no matter what kind of dehydration, body fluid moisture is reduced, resulting in loss of body fluid.

one Hypertonic dehydration Hypothalamus Thirst When the center is stimulated, the conscious person will feel thirsty and ask for water. At the same time, the anterior hypothalamus optic nerve The upper nucleus is stimulated to release antidiuretic hormone, which acts on the distal convoluted tubules and collecting ducts of the kidney through blood circulation, so that water absorption increases and urine volume decreases significantly. After the regulation of drinking water and oliguria, the water in the body returns to normal, and then hyperosmolar becomes Isotonic , the total body fluid also recovered, so Mild dehydration Although it happens frequently, it will not cause serious illness; However, if the dehydration is serious, especially if the regulation function is abnormal, the patients often present symptoms of different degrees. Hypertonic dehydration Except for thirst, people often show Skin mucosa dry, Facial flushing , restless. Children are prone to dehydration fever, decreased urine volume and weight loss. As the blood volume decreases, the blood pressure decreases significantly, which can cause shock. Because of insufficient renal blood circulation, Non protein nitrogen etc. Metabolites Caused by detention Prerenal Azotemia And Acidosis 。 Brain cell Dehydration can cause psychoneurological syndrome and eventually coma. here Blood concentration ， blood corpuscle Number hemoglobin , hematocrit and blood Na+can be increased, Plasma osmolality It also obviously exceeds the normal upper limit. Urine is concentrated with high specific gravity.

two Isotonic dehydration When thirst is not obvious, Hypotonic dehydration When the patient is not thirsty Have original The symptoms of the disease are mainly electrolyte deficiency and sodium loss, etc Acid base balance disorder Performance. When dehydration exceeds 2% - 3% of body weight, and blood Na+<125mmol/L, patients feel tired and weak, weak limbs, dizziness, headache, mental fatigue, and sometimes nausea. When sodium loss per kilogram of body weight（ NaCl ）When it reaches 0.5-0.75g, blood volume and blood pressure often decrease（ systolic pressure <12kPa) Pulse fineness 、 Blurred vision 。 When the sodium loss per kilogram of body weight reaches 0 75-1 . 25g, there is apathy Stupor , shock and coma, with little or no sodium in urine (<10mmol/L). Early cause of urine volume Plasma osmolality The antidiuretic hormone is inhibited but may not be reduced, but the urine volume in the later stage is reduced, and the patient is often dry Peripheral circulatory failure 。 Blood Na+and Cl - are often reduced, but due to kidney blood Circulatory disorder , non protein nitrogen creatinine 、 urea It can also increase, and the blood is also concentrated.

[Western medicine treatment]: Hypertonic dehydration 0.45% NaCl solution (semi osmotic solution) shall be given.

Isotonic dehydration and Hypotonic dehydration Patients need supplementation normal saline or glucose Salt water. In case of severe sodium loss, 3% - 5% NaCl solution can also be added. Attention should also be paid to correcting the disorder of potassium metabolism and acid-base balance during fluid replacement. In addition, no matter what kind of dehydration, except Symptomatic treatment Outside, Etiological treatment It is also an important principle. The treatment is mainly to supplement water and electrolyte. General Isotonic solution 5% glucose or normal saline. Volume of fluid replacement It can be simply calculated as 1% of the body weight of water loss and 1000ml of additional liquid needed. It can also be calculated according to the measured value of blood sodium. The following formula can be used for reference:

what is needed fluid infusion Amount (ml)=4 × body weight (kg) × (blood sodium mmol/L-142) Replenishment speed 。 Such as Department Center Severe dehydration 1/2-1/3 of the fluid supplement volume can be calculated within 4-8h; The rest can be supplemented within 24-48h. At the same time, we should closely observe the clinical changes, and judge whether the amount of fluid infusion is sufficient according to the reaction after fluid infusion. If possible, the central venous pressure can be measured to monitor the infusion speed.

Words · Dehydration

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Pinyin: ABCD

[Explanation of words]

◎ Dehydration

[ dehydrate ]Material loses moisture

◎ Dehydration

[loss of body fluids] Disease name. The fluid in the human body is greatly reduced, which often occurs in severe vomiting, diarrhea, sweating, bleeding, etc

[Detailed explanation]

(1) . Disease name. In the case of severe vomiting, diarrhea or a lot of sweating and bleeding, the fluid in the human body is greatly reduced. The symptoms are thirst xerosis cutis , sunken eyeball, decreased urine output, etc.

(2) . The substance loses moisture. If the crystal is lost Crystal water The compound loses hydrogen and oxygen atoms equivalent to water.

(3) . It is an operation to reduce moisture in materials. There are special dewatering machines, such as Centrifugal dehydrator 、 Thickener 、 filter 、 dryer Etc. Air drying is also a method of dehydration.

Hypertonic dehydration

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Hypertonic dehydration (hypertonic dehydration) Serum sodium Concentration>150mmol/L (150mEq/L) Plasma osmolality >310mOsm/L is the main feature. 1. Cause and mechanism

(1) . Simple water loss

① Transpulmonary dehydration: caused by any reason Hyperventilation Can be used respiratory tract Mucous Insensitive evaporation Strengthen to cause a large amount of water loss;

② Transdermal water loss: e.g fever or Hyperthyroidism It can lose several liters of water every day through unconscious evaporation of the skin;

③ Renal dehydration: Central diabetes insipidus Due to insufficient generation and release of ADH, Renal diabetes insipidus Chronogenic kidney Distal convoluted tubule and Manifold Lack of response to ADH, so the kidney can excrete a lot of water. Water loss occurs in Nephron The farthest part of the Sodium ion Has been Reabsorption 。 Therefore, the patient can discharge 10-15L of diluted urine, which only contains a few mmol Sodium.

The total sodium content of the body can be normal during simple dehydration.

(2) Water loss is greater than sodium loss: that is, loss of hypotonic fluid, which can be seen in:

① Gastrointestinal fluid loss: low sodium content may be lost during vomiting and diarrhea Digestive juice , such as some Infantile diarrhea The fecal sodium concentration was below 60 mmol/L;

② Excessive sweating: sweating is hypotonic fluid; When sweating heavily, about 800ml of water can be lost per hour.

③ Transrenal loss Hypotonic urine : such as repeated intravenous infusion mannitol 、 urea 、 Hypertonic glucose Isochronous Renal tubular fluid osmotic pressure Caused by elevation Osmotic diuresis , water drainage is more than sodium drainage.

In these cases, the body loses both water and sodium, but the loss of water is disproportionately more than that of sodium.

(3) Insufficient drinking water

The above reasons are seldom caused when people with normal thirst can get and drink water Hypertonic dehydration Because in the early stage of water loss, Plasma osmolality A slight increase will stimulate the thirst center. After drinking water, Plasma osmolality Is restored. Therefore, it is only obvious that Hypertonic dehydration : ① Water source cut off: such as desert Getting lost; ② Unable or unable to drink water: such as patients who frequently vomit, comatose patients, extremely weak patients, etc.; ③ Dysfunction of thirst: hypothalamus The lesion can damage the thirst center; Some do not cause aphasia Of cerebral cortex Cerebrovascular accident Of the elderly patients, thirst disorders can also occur. On clinical practice Medium, Hypertonic dehydration The causes of hyperosmotic dehydration are often comprehensive, such as loss of hyperosmotic dehydration in infants with diarrhea intestinal juice 、 Water ingress In addition, there is excessive water loss caused by factors such as fever, sweating and faster breathing.

2. Impact on the body

(1) More water loss than sodium loss, Extracellular fluid The increase of osmotic pressure stimulates the thirst center (except for those with thirst disorders), prompting patients to find water to drink.

(2) Removal Diabetes insipidus In addition to patients, Extracellular fluid Hyperosmolality stimulates hypothalamus Osmoreceptor It increases the release of ADH, which increases the reabsorption of water by the kidney, Urine output Reduce and increase the specific gravity.

⑶ Extracellular fluid The increase of osmotic pressure can make the osmotic pressure relatively low Intracellular fluid The water in is transferred out of the cell. The above three points can make Extracellular fluid Get water supplement, so that osmotic pressure tends to fall back.

so Hypertonic dehydration Both the intracellular and extracellular fluid decreased, but Extracellular fluid It may be supplemented from several aspects, so extracellular fluid and Blood volume Less than Hypotonic dehydration It is obvious that there are fewer patients with shock.

⑷ Early or mild patients, due to Decreased blood volume Not obvious, aldosterone secretion does not increase, so there is still sodium excretion in urine, and its concentration can also increase due to increased water reabsorption; In advanced and severe cases, blood volume may decrease aldosterone Increased secretion Urinary sodium The content decreases.

⑸ Extracellular fluid When osmotic pressure increases Brain cell dehydration Can cause a series of central nervous system dysfunction Symptoms of, including Lethargy , muscle twitching, coma, and even death. Brain volume shrinks significantly due to dehydration Vascular tension Increase, which may lead to vein rupture and local appearance Intracerebral hemorrhage and Subarachnoid hemorrhage 。

(6) Severe cases of dehydration, especially children, may occur because the water evaporated from the skin is reduced and the heat dissipation is affected Dehydration heat 。

According to the degree of dehydration Hypertonic dehydration It is divided into mild, moderate and severe grades. ① light: Water loss It is equivalent to 2-5% of the body weight. The patient's mucous membrane is dry and sweats less, Skin elasticity Decreased, thirsty, low urine output, urine osmolality usually>600mOsm/L, Specific gravity of urine >1.020 (For patients with renal concentration dysfunction, such as Diabetes insipidus Except patients), acidosis may occur, but shock does not occur, infants and young children cry without tears, the anterior chimney is sunken, and the eyeball tension is low. ② Moderate: water loss is equivalent to 5-10% of body weight. clinical manifestation Have severe thirst, nausea, armpit and groin Dry skin, lack of elasticity, Blood concentration ， Tachycardia ， Orthostatic hypotension ， Central venous pressure Falling, indifferent expression, renal function Low, Oliguria , Plasma creatinine and urea The level of nitrogen increases, Serum potassium The concentration can be at the upper limit of the normal range or slightly higher, Urine osmolality Usually more than 800mOsm/L, urinary specific gravity>1.025 (for patients with kidney concentration dysfunction Diabetes insipidus Except for patients, etc.) Acidosis 。③ Severity: water loss is equivalent to 10~15% of body weight. The patient often has shock, and the main clinical manifestations are oliguria or Anuria , blood pressure drops, pulse is fast and weak. Impaired renal function, plasma creatinine and urea Nitrogen increase; Serum [K+] increased. Metabolic acidosis Usually serious. Severe dehydration It can often lead to death. Few people can tolerate dehydration beyond this limit.

3. The principle of prevention and treatment should first prevent the primary disease and prevent the effect of some reasons. Hypertonic dehydration Because of high blood sodium concentration, 5% glucose solution should be given. In patients with severe hypernatremia, 2.5% or 3% glucose solution can be injected intravenously. It should be noted that, Hypertonic dehydration When the blood sodium concentration is high, but the patient still has sodium loss, so a certain amount of sodium containing solution should be supplemented to avoid the occurrence of Extracellular fluid Low permeability.

Hypotonic dehydration

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Hypotonic dehydration is characterized by more sodium loss than water loss, serum sodium concentration<130mmol/L (<130mEq/L), Plasma osmolality 280mOsm/L is the main feature. 1. Cause and mechanism

(1) Loss of a large amount of digestive fluid and only supplement of water: this is the most common reason. Most of them were due to vomiting and diarrhea, and some of them were due to the loss of body fluid during gastric and intestinal suction, and only water was added or glucose solution was transfused.

⑵ Only supplement water after sweating: Although sweating is hypotonic fluid, a large amount of sweating can also be accompanied by significant sodium loss (about 30~40mEq of sodium can be lost per hour). If only supplement water, it can cause Extracellular fluid Low permeability.

(3) Large area burn ： Burn area Large, a large amount of body fluid is lost and only Make up water May occur Hypotonic dehydration 。

⑷ Renal sodium loss: it can be seen in the following situations: ① edema patients use sodium excretion continuously for a long time diuretic (e.g Chlorothiazide Class A, furosemide and Diuretic acid Etc.), due to Nephron The reabsorption of sodium in the dilution section is inhibited, so a large amount of sodium is lost from the urine. If sodium salt intake is restricted again, the lack of sodium is more obvious; ② Acute renal failure Period of polyuria, mainly Renal tubule In liquid urea etc. solute concentration Increase, so it can pass Osmotic diuresis Acting cause Renal tubular epithelial cells Reduction of sodium and water reabsorption; ③ In the so-called“ Desalinization nephritis ”Of patients, due to the damage of renal tubular epithelial cells to aldosterone Reactivity It is decreased, so the cells in the distal renal tubule (some people think it is the collecting duct in recent years) have an obstacle to sodium reabsorption; ④ In Addison's disease, the main reason is that the secretion of aldosterone is reduced, so the renal tubules have less sodium reabsorption. For the above patients who lose sodium through the kidney, if only water is added and sodium salt is ignored, it may cause Hypotonic dehydration 。

thus it can be seen, Hypotonic dehydration The occurrence of sodium deficiency is often related to improper measures (only adding water instead of sodium after sodium loss). This point deserves full attention. However, it must be pointed out that even without these inappropriate measures, the loss of a large amount of body fluid itself can cause some patients to suffer Hypotonic dehydration 。 This is due to the loss of a large amount of body fluid Extracellular fluid The significant reduction of capacity can be achieved by Volume receptor The stimulation of ADH causes an increase in ADH secretion, which results in an increase in water reabsorption by the kidney, thus causing extracellular fluid hypotension（ Hypotonic dehydration ）。

2. Impact on the body Extracellular fluid When the capacity has not been reduced Extracellular fluid The osmotic pressure is reduced and ADH secretion is reduced, so the water reabsorption of renal tubular epithelial cells is reduced, leading to the increase of water excreted by the kidney. Therefore, early patients can excrete more hypotonic urine. The increase of water discharge can, on the one hand Extracellular fluid The volume is further reduced, which can make the patient prone to shock, on the other hand Extracellular osmotic pressure It has been recovered to a certain extent, so it has a certain compensatory significance. If Extracellular fluid If the osmotic pressure of is still not recovered, the extracellular fluid can be transferred to the cells with relatively high osmotic pressure, so the intracellular fluid is not lost, but the amount of extracellular fluid is significantly reduced, and the patient is prone to shock, which is the main feature of this type of dehydration. In addition, due to low blood sodium concentration, Macula densa (located at the beginning of distal convoluted tubule). so renin — Angiotensin - The activity of aldosterone system is increased and the secretion of aldosterone is increased, which can increase the reabsorption of sodium by renal tubular epithelial cells and reduce the excretion of Na+or Cl - in urine. Renin - Angiotensin - The increased activity of aldosterone system is also associated with extracellular fluid, especially Effective circulating blood volume Decrease, so that the kidney Afferent arteriole Pressure reduction Stretch receptor Be excited, thus increase the release of renin.

When dehydration further develops Extracellular fluid When the volume is seriously insufficient, the secretion of ADH can be increased due to stimulation of the volume receptor, thus increasing the water reabsorption of the kidney. The result is that on the one hand, the volume of extracellular fluid can be maintained to a certain extent, so that it will not be excessively reduced; on the other hand, the osmotic pressure of extracellular fluid can be reduced, thus promoting the water transfer to the cells. Clinically, patients often have venous collapse arterial pressure Decreased, fine pulse, cold limbs, decreased urine output, azotemia, etc. because Extracellular fluid especially Intercellular fluid Significantly reduced, resulting in loss of skin elasticity, eye sockets and infants Fontanelle Invagination 。

According to the degree of sodium deficiency and clinical symptoms Hypotonic dehydration It is divided into three degrees: ① Mild: equivalent to weight loss per kilogram of adult sodium chloride 0.5g。 Patients often feel tired dizzy , fainting may occur when standing upright（ faint ）, little or no sodium chloride in urine; ② Moderate: 0.5g-0.75g sodium chloride is lost per kilogram of body weight. At this time, the patient may have anorexia , nausea and vomiting Blurred vision Slight decrease in systolic blood pressure, fainting when standing up, fast heart rate, weak pulse, weak skin elasticity, thin face, etc.; ③ Severe: 0.75g~1.25g sodium chloride is lost per kilogram of body weight, and the patient may have nervous symptoms such as apathy and numbness. Finally, coma occurred and severe shock occurred.

3. Prevention and control principle: remove the causes (such as shutdown) Diuretic ）In addition to prevention and treatment of primary diseases, isotonic sodium chloride solution is generally used to replenish blood vessels in time Internal capacity The purpose of treatment can be achieved. If shock has occurred, timely and active rescue is required.

Isotonic dehydration

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Isotonic dehydration can be caused when water and sodium are lost in proportion to their concentration in normal plasma. Even if it is not lost in proportion, it will be regulated by the body after dehydration. Those whose blood sodium concentration remains at 130~145mmol/L and osmotic pressure remains at 280~310mOsm/L are also isotonic dehydration. 1. Cause and mechanism

⑴ Loss of intestinal fluid: from duodenum reach Ileocecal part All small intestines of Secretory fluid as well as bile and Pancreatic juice The concentration of sodium is between 120 and 140 mmol/L. Therefore, Enteritis minor Diarrhea Intestinal fistula 、 Small intestinal obstruction May cause the loss of isotonic body fluid.

(2) Large amount Hydrothorax and ascites Formation, etc.

2. Impact on the body Extracellular fluid The volume decreased while the osmotic pressure was within the normal range, so the water balance between the intracellular and extracellular fluid was maintained, and the intracellular fluid volume did not change significantly. The decrease of blood volume can increase the reabsorption of sodium and water by the kidney through the increase of aldosterone and ADH, thus Extracellular fluid It is supplemented to a certain extent, and the urine sodium content decreases, Specific gravity of urine increase. If the blood volume decreases rapidly and severely, the patient may also have shock.

If not treated in time, it can be changed into Hypertonic dehydration ； If only water is added without sodium salt, it can be transformed into low permeability dehydration. (See Table 5-1 for comparison of three types of dehydration).

3. The principle of prevention and treatment is to prevent and control the primary disease. Infusion of sodium chloride solution with low osmotic pressure, and its osmotic pressure should be 1/2~2/3 of the osmotic pressure of isotonic solution.

Dehydration mechanism

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No matter what type of dehydration they all have dehydration at first, that is, there is a decrease in the volume of extracellular fluid. The extracellular fluid accounts for about 20% of the body weight of normal adults, while the intracellular fluid accounts for 40% of the body weight. The extracellular fluid is divided into plasma (5% of body weight) and interstitial fluid (15% of body weight). Under normal circumstances, there are considerable differences in body fluid volume between different individuals, which mainly depends on age, sex and obesity. The distribution of plasma interstitial fluid and intracellular fluid is relatively stable, and they are constantly exchanged. There is a layer between plasma and interstitial fluid Capillary wall Materials other than protein can be freely permeable, so the liquid balance on both sides of the capillary is mainly maintained by colloid osmotic pressure and capillary hydrostatic pressure, that is, blood pressure in the capillary. Between interstitial fluid and intracellular fluid cell membrane Separate cell membrane from water and some Small molecule Solute (e.g urea ）It can be permeable. Colloids such as protein cannot pass through. Although electrolytes such as sodium and potassium can enter and exit the cells, they are subject to the sodium pump (the cell membrane is not loud, and the blood pressure is generally not low. If the cause of hypertonic dehydration continues to exist, and dehydration continues to worsen to moderate dehydration (weight loss is more than 4%), The increase of aldosterone secretion is an important hormone regulating blood volume and extracellular fluid volume. Hypertonic dehydration further develops that blood volume cannot be maintained, and circulatory failure symptoms appear when blood pressure falls on the bed. In case of severe dehydration, the water evaporated from the skin decreases, the temperature regulation is affected, and the temperature rises. It is clinically called dehydration heat. Because the water inside the cells is transferred to the extracellular fluid, it causes cell dehydration. In clinical practice, brain cell dehydration is more obvious, and the symptoms of central nervous system dysfunction caused by it. In addition, cell dehydration causes cell metabolism disorder, Increased catabolism and decreased excretion of incompletely oxidized combined metabolites from the kidney may lead to azotemia. The serum sodium concentration will inevitably increase during hypertonic dehydration. 2、 Osmotic dehydration

The body is dehydrated and sodium loss is greater than water loss. Because the osmotic pressure of extracellular fluid is reduced, the reflex inhibition of the release of antidiuretic hormone from the posterior pituitary will weaken the reabsorption of water by the distal renal tubules, so the early urine volume of hypotonic dehydration does not decrease, and the relative density of urine is reduced. Because the osmotic pressure of extracellular fluid is lower than that of intracellular fluid, the water in extracellular fluid is also transferred to the cells, The intracellular fluid is not reduced, sometimes it can be slightly increased, while the extracellular fluid is significantly reduced. Because the extracellular fluid is significantly reduced, the body surface symptoms of dehydration appear early and obvious, and the symptoms of circulatory failure appear early and obvious. Due to the decrease of extracellular fluid volume and the increase of aldosterone secretion, as well as the late circulatory failure, the renal blood flow is low; The decrease of glomerular filtration rate leads to a decrease in urine volume, a significant decrease in the content of sodium chloride in urine, and when azotemic hypotonic dehydration occurs, the intracellular J fluid is hypotonic. Therefore, in the late stage without thirst symptoms, brain cell edema may also lead to water poisoning, resulting in dysfunction of the central nervous system.

3、 Isotonic dehydration

Dehydrated water and steel in the machine body are lost according to the proportion of normal body fluid, or a certain amount of water is supplemented by hypertonic dehydration. Since it is isotonic dehydration without the influence of osmotic pressure factors, but due to the lack of extracellular fluid capacity, Effective circulating blood volume The decrease can also stimulate the volume receptor, causing an increase in the release of ADH and aldosterone, increasing the reabsorption of water pins by the kidney, which is conducive to the maintenance of extracellular fluid volume. In general, the decrease of blood volume up to 10% can cause the increase of ADH release. In clinical practice, moderate osmotic dehydration is most common in patients with decreased urine volume and decreased urine sodium. If the isotonic dehydration is not treated, it can be transformed into hypertonic dehydration due to the loss of water such as the water exhaled from the lungs evaporated from the skin. If only water is added but no sodium salt is added, it can be transformed into hypotonic dehydration. If dehydration is further developed, the volume of extracellular fluid is significantly reduced, and in addition to the dehydration symptoms on the body surface, blood pressure can also drop, shock and even renal failure can occur.

According to weight loss (water loss) and clinical manifestations, dehydration is divided into three degrees:

l. Mild dehydration and water loss account for 2% - 3% of body weight or 5% of body weight loss, with only general neurological symptoms, such as headache, dizziness, weakness, and slightly reduced skin elasticity. Hypertonic dehydration has thirst.

3. Severe dehydration and water loss account for more than 6% of body weight or more than 10% of body weight loss. The above symptoms and signs become worse, and even shock and coma occur.

Health tips

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In people with normal thirst, hypertonic dehydration is rarely caused when water is available and can be drunk, because in the early stage of water loss, when the plasma osmotic pressure slightly increases, the thirst center will be stimulated. After drinking water, the plasma osmotic pressure can be recovered. Dehydration press Extracellular fluid There are three types of osmotic pressure. with water loss The main one is called hypertonic (primary) dehydration; Hypotonic (secondary) dehydration is mainly caused by sodium loss; The loss of water and sodium in proportion to their content in plasma is called Isotonic dehydration 。

It is only obvious that Hypertonic dehydration ：

1. The water source is cut off: such as getting lost in the desert;

2. Cannot or cannot drink water: such as patients who frequently vomit, coma patients, extremely weak patients, etc;

3. Dysfunction of thirst: Hypothalamic lesions can damage the thirst center; Some do not cause aphasia Of cerebral cortex Cerebrovascular accident Of the elderly patients, thirst disorders can also occur. Water loss is greater than sodium loss: loss of hypotonic fluid:

1. Gastrointestinal fluid loss: low sodium content may be lost during vomiting and diarrhea Digestive juice , such as some Infantile diarrhea The fecal sodium concentration was below 60 mmol/L;

2. Excessive sweating: sweating is hypotonic fluid; When sweating heavily, about 800ml of water can be lost per hour.

3. Loss of hypotonic urine through the kidney: such as repeated intravenous infusion mannitol 、 urea 、 Hypertonic glucose Isochronous Renal tubular fluid osmotic pressure Caused by elevation Osmotic diuresis , water drainage is more than sodium drainage.

Prevention and control principle

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1. The primary disease should be prevented to prevent the effect of some reasons. Hypertonic dehydration Because of high blood sodium concentration, 5% glucose solution should be given. Hypernatremia In severe cases, 2.5% or 3% glucose solution can be injected intravenously.

2. It should be noted that the blood sodium concentration is high when hypertonic dehydration occurs, but the patient still has sodium loss, so a certain amount of sodium containing solution should be supplemented to avoid occurrence Extracellular fluid Low permeability.

Dehydration in chemistry

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This is a chemical change, also called corrosion. It means that the hydrogen Oxygen atom , according to water The molecular composition ratio (H20) is hydrogen: oxygen=2:1.

This process does not remove water molecules, but hydrogen and oxygen elements in the material.

For example, concentrated sulfuric acid With strong Dehydration , can transform paper, wood, skin sucrose (Three kinds of C H O Element composition ）Take off the hydrogen and oxygen elements in. Since the H O element is gone, only the C element is left, and they become black carbon.

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