Dehydration

Introduction to dehydration The sodium salt (NaCl, NaHCO3) is the main inorganic salt that determines the osmotic pressure of extracellular fluid. Therefore, the serum sodium concentration is the main factor determining the plasma osmotic pressure. Due to the difference in the ratio of water and sodium deficiency, different plasma sodium concentrations are changed. Osmotic pressure changes. When dehydration, dehydration is often divided into three types according to the level of serum sodium: clinical isotonic dehydration, hypotonic dehydration and hypertonic dehydration. basic knowledge Sickness ratio: 0.5% Susceptible people: no specific population Mode of infection: non-infectious Complications: edema, narcolepsy, coma

Dehydration cause

Loss through the digestive tract (15%):

Vomiting, diarrhea, gastrointestinal drainage, intestinal pancreaticobiliary and other causes of loss of digestive juice, although the sodium concentration in the digestive juice is slightly lower than the sodium concentration in the plasma, but most patients can supplement a certain amount of water by oral administration, so the plasma osmotic pressure is mostly normal. .

Drainage (18%):

It usually occurs in patients with leakage, mainly in patients with heart, liver and renal insufficiency. Because the substances in the leakage (except protein) are similar to plasma, isotonic dehydration is easy.

Major bleeding (12%):

At this time, the water and electrolyte in the plasma are lost in the normal proportion.

Loss through the skin (10%):

Most patients with skin loss have more water loss than sodium loss, and hyperosmotic dehydration is prone to occur. However, some patients with burns and exfoliative dermatitis have a large amount of exudate through the wound surface. The ratio of water loss and sodium loss is basically the same, which can also cause isotonicity. Dehydration.

Loss by kidney (15%):

In patients with renal tubular dysfunction or various diabetes insipidus, the renal tubules are unable to effectively concentrate the water. The ratio of water loss and sodium loss is similar to that of glomerular filtrate, resulting in isotonic dehydration.

Improper dehydration treatment (10%):

Hypertonic or isotonic water loss corrects the process of hydrating too much, while electrolytes, especially sodium chloride, are insufficiently replenished.

Renal impairment (8%):

Urgent, chronic renal insufficiency in the polyuria, salt-salt nephritis, renal tubular acidosis, due to the decline in the patient's kidney sodium retention function, individual patients with sodium loss can reach 100mmol per day.

Use of diuretics (12%):

Appropriate electrolyte concentration is the premise of diuresis. Furosemide diuretics and thiazide diuretics mainly produce diuretic by inhibiting the reabsorption of electrolytes Na, Cl-, K, so long-term application will lead to electrolyte loss. Insufficient supplementation such as sodium chloride may easily lead to hypotonic dehydration.

Pathogenesis

The balance of water metabolism includes water intake and production as well as excretion. The normalization of the thirsty center, the normal function of the kidney dilution and concentration, the secretion and function of vasopressin play an important role, and the dynamic balance between the two is broken. Make water metabolism in a state of disorder.

Isotonic dehydration is mainly the loss of extracellular fluid volume, blood volume can be significantly reduced, and there is a manifestation of insufficient blood volume, but because the plasma osmotic pressure is in the normal range, the intracellular fluid does not change much, due to the decrease in blood volume, kidney Excitatory, angiotensin-aldosterone system excites, sodium, water reabsorption increases; stimulates secretion of antidiuretic hormone, further increases water reabsorption.

In hypotonic dehydration, due to the decrease of plasma osmotic pressure, the difference of osmotic pressure between extracellular fluid and intracellular fluid, through the regulation of osmotic mechanism, the transfer of water in the extracellular fluid to the intracellular fluid, cell edema occurs, and The extracellular fluid capacity is further reduced.

The decrease of plasma osmotic pressure reduces the release of ADH and increases the drainage of the kidney. Therefore, in the early stage, more hypotonic urine can be discharged to maintain the balance of osmotic pressure inside and outside the cell. This effect occurs earlier than the transport of water inside and outside the cell. Therefore, although there is dehydration, the amount of urine is not reduced, hyponatremia and decreased blood volume, can also stimulate the increase of aldosterone secretion, increase sodium, water reabsorption.

For the above reasons, the reduction of extracellular fluid volume during hypotonic dehydration is more pronounced, and the symptoms and signs of extracellular fluid volume reduction are more pronounced than isotonic dehydration.

Dehydration prevention

Active treatment of primary disease, complications.

1. When isotonic dehydration has hypovolemic shock, simple rehydration is forbidden.

2. Hypotonic dehydration is contraindicated with early supplementation of 5% or 10% glucose solution.

3. Hyperosmolar dehydration occurs when severe hypernatremia occurs, it is contraindicated to quickly enter hyperosmotic syrup, so as not to aggravate brain edema.

Dehydration complications Complications, edema, narcolepsy, coma

Cerebral edema may occur when hypotonic dehydration is severe, and lethargy or coma may occur when brain cells are edematous.

Dehydration symptoms Common symptoms Renal tubular acidification dysfunction Ketoacidosis Loss of water fainting oliguria Hyperosmolar coma Dizziness Diabetes dehydration Abdominal pain

Isotonic dehydration mainly manifests as low blood volume status such as fatigue, fatigue, dizziness when standing up, and even syncope, unconsciousness, some patients may have symptoms of insufficient blood supply to organs such as chest pain, abdominal pain, common signs of skin elasticity Poor, dry skin mucosa, pulse speed is accelerated and weak, superficial veins are collapsed, limbs are cold, and urine output is reduced.

Patients with hypotonic dehydration have no thirst, and the skin and mucous membranes are dehydrated. The symptoms and signs of hypovolemia and cerebral edema are similar to those of sodium-deficient hyponatremia.

Isotonic dehydration

(1) Loss of body fluid through the digestive tract is the most common cause. Due to the loss of upper digestive tract fluid, H is mainly accompanied by metabolic alkalosis. The lower digestive tract fluid contains more alkali and is prone to metabolic acidosis. Therefore, in the diagnosis of isotonic dehydration, attention should be paid to the imbalance of acid-base balance.

(2) heart, liver, kidney dysfunction, more serous effusion, repeated large number of chest, abdominal puncture drainage, prone to isotonic dehydration, should pay attention to a drainage volume of not more than 1000ml, pay attention to observe With or without hypovolemic status and timely treatment.

(3) The proportion of body fluids in elderly patients is only 45%, and the thirst feels less than young people, while the dry skin, decreased elasticity, tachycardia, orthostatic hypotension and other signs of dehydration are easily overlooked, so special attention should be paid. Whether the patient has oliguria or no urine, whether the oral mucosa is less or less, whether there is abnormality in the state of consciousness, whether the blood pressure in the resting state is low, and whether there is any loss of body fluid in the medical history.

(4) The amount of urine is a powerful indicator of whether the amount of body fluid is sufficient. Usually, the amount of urine <1000ml means more reduction of extracellular fluid, but attention should be paid to certain special conditions, such as poor glycemic control of diabetes, especially diabetic hypertonicity. In patients with coma or ketoacidosis, due to the presence of osmotic diuresis, even if hypovolemic shock has occurred, the urine volume can sometimes be >1500ml/d. At this time, the urine volume cannot be used as an indicator to determine whether the effective blood volume is normal.

(5) Note that effective blood volume and extracellular fluid are not equivalent: some patients have increased interstitial fluid, subcutaneous edema, and bright skin. At this time, the extracellular fluid is normal, and the effective blood volume is insufficient, which often causes blood pressure to drop. .

2. Hypotonic dehydration

(1) Diagnosis of hypotonic dehydration should pay attention to the medical history, because most of them are caused by improper dehydration or improper use of diuretics, sodium loss is more than water loss, serum sodium <135mmol / L, plasma osmotic pressure <280mOsm / L.

(2) In the case of hypotonic dehydration, since the serum sodium is low and the water is transported from the extracellular to the cells, the manifestation of insufficient blood volume is heavier than isotonic dehydration, and there is a manifestation of cerebral edema and the patient has no thirst.

(3) Early urine volume is not reduced, once the decrease in urine volume indicates low blood sodium and severe blood volume.

3. Hypertonic dehydration

(1) Seen in some diseases with acute dehydration greater than sodium loss: such as diabetic hyperosmolar coma, diabetes insipidus did not timely replenish water, it should be noted that both cases are dehydrated by the kidney, so in severe dehydration, the patient still has A large amount of urination, the amount of urine does not represent the true state of fluid loss and blood volume reduction.

(2) The symptoms and signs of the central nervous system often mask the manifestations of insufficient blood volume, and become the main cause of patient visits. The diagnosis should be misdiagnosed and missed, especially when the patient cannot provide or know the history of the primary disease.

Dehydration check

1. Isotonic dehydration laboratory examination

(1) Blood concentration: red blood cells (RBC), hemoglobin (Hb), hematocrit (HCT), plasma protein concentration increases, or the concentration of the base value increases, but blood loss occurs in blood loss.

(2) Red blood cell morphology: normal, mean red blood cell volume (MCV), mean red blood cell hemoglobin concentration (MCHC) were normal.

(3) Urine examination of urine sodium, urine chlorine concentration and 24h discharge decreased, urine relative density increased.

2. Hypotonic dehydration blood test indicators

(1) Serum sodium concentration: decreased, less than 135mmol / L, more often associated with hypochloremia, and the degree of decline is generally the same, the blood potassium concentration can be normal or elevated.

(2) The plasma osmotic pressure decreases.

(3) Blood concentration: red blood cell count, hemoglobin, plasma protein and hematocrit are both increased, and the value is greater than the basic value.

(4) Erythrocyte edema: The water in the red blood cells increases, the average red blood cell volume increases, and the average red blood cell hemoglobin concentration decreases.

(5) Common urine test indicators:

1 urinary sodium concentration: decreased by extrarenal factors, more than 15mmol / L, or even not detected; renal dysfunction, abnormal regulation mechanism or patients with diuretics increased urinary sodium, more than 20mmol / L, in the absence Patients with sodium should be routinely examined for urinary electrolytes, as even patients with low sodium caused by extrarenal factors may be accompanied by a decline in renal reabsorption, such as the elderly, chronic hypokalemia, and patients taking aminoglycosides.

2 urinary chloride concentration: consistent with changes in urinary sodium concentration.

3 discharge: decreased by extrarenal factors, 24h urine sodium and urinary chlorine emissions were significantly reduced, and even not measured.

In patients with impaired renal function, abnormal regulation mechanisms, or diuretics, 24h urinary sodium and urinary chloride excretion are still high, even far beyond the normal range, which is one of the reasons for some patients with refractory hyponatremia.

4 urine osmotic pressure and urine relative density: generally consistent with changes in urinary sodium concentration, patients with hyponatremia caused by extrarenal factors due to good electrolyte absorption, osmotic pressure and relative density are very low; but less urinary (metabolism waste concentration); and the kidney itself causes a large variation, the level of which depends mainly on the ratio of water and solute, generally similar to plasma.

According to the condition, clinical manifestations can be done:

1. Central venous pressure examination: normal value 6 ~ 12cmH2O (1cmH2O = 0.098kPa), a decrease in central venous pressure suggests insufficient blood volume.

2. ECG, B-ultrasound, X-ray examination, etc.

Dehydration diagnosis

Clinically, according to medical history, symptoms and signs, it is not difficult to make a diagnosis of dehydration. After the diagnosis of dehydration is made, according to the serum sodium concentration, which type of dehydration can be determined.

1. Mild dehydration: water loss accounts for 2%-3% of body weight or 5% of body weight, only general neurological symptoms such as headache, dizziness, weakness, slight decrease in skin elasticity, hypertonic dehydration and thirst .

2. Moderate dehydration: water loss accounts for 3%-6% of body weight or 5%-10% of body weight loss. The symptoms of dehydration are obvious, and symptoms of circulatory insufficiency begin to appear.

3. Severe dehydration: The amount of water loss accounts for more than 6% of body weight or more than 10% of body weight loss. The aforementioned symptoms are aggravated, and even shock and coma occur.

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