Water balance characteristics of the elderly Water accounts for 60% of body weight in the composition of the human body, about 55% of female young people, with age, fat and muscle reduction, the overall water is also declining, about 45% of the elderly. Water is necessary for cell metabolism and maintenance of life, and the balance of water is mainly regulated by the anti-diuretic hormone secreted by the posterior pituitary gland and the kidney’s ability to excrete water. In the elderly, water intake is reduced due to increased thirst threshold and decreased thirst due to dryness of the mouth, decreased sense of taste, diminished intelligence, and poor responsiveness. The renal tubular responsiveness to antidiuretic hormone and aldosterone decreases, the concentration function of the kidney decreases, and the regulation of water balance becomes impaired, so the elderly can still excrete more water from the kidney when they are dehydrated. Some other diseases such as infection, fever, sweating, impaired consciousness, cerebrovascular disease, diabetes, gastrointestinal disease, and use of diuretics are common triggers of dehydration. Insufficient intravascular volume can also be present in cardiac and renal insufficiency and in severe liver disease with ascites. Clinical manifestations of dehydration in the elderly True volume deficiency may cause dizziness or syncope, weakness and thirst and reduced urine output in mild cases, or postural hypotension or resting hypotension, weakness, drowsiness, mental disturbance, and oliguria or anuria in severe cases. Severe dehydration may present with shock or near shock. Poor skin elasticity is not a sign of dehydration in the elderly, and the areas where dry skin is most likely to be found are the axillae and groin. It is easily misdiagnosed due to the coexistence of multiple diseases such as cardiac insufficiency, prolonged bed rest, diabetes mellitus, application of antihypertensive and diuretic drugs that make the body’s compensatory response to fluid loss poor, or masked by the primary disease. The amount of extracellular fluid is normal or even increased in circulating hypovolemia without fluid loss, such as heart failure, cirrhosis, and nephrotic syndrome with severe hypoproteinemia, which results in low effective blood volume due to water and sodium distribution to subcutaneous and third body cavities. Laboratory tests may reveal elevated levels of hemoglobin, blood urea nitrogen, and serum creatinine, increased erythrocyte product, increased sodium concentration, and decreased urinary sodium. A difference in diastolic blood pressure of 10 mmHg or more in the sitting and lying positions is a reliable indicator of hypovolemia. Treatment of dehydration in the elderly The first thing is to replenish the effective circulating blood volume. 5% glucose is evenly distributed after input into the body, and 1 liter only replenishes 75 ml of blood volume, while 0.9% sodium chloride is distributed in the extracellular fluid after input into the body, and 1 liter can replenish 200 ml of blood volume, and the colloidal solution replenishes more blood volume. Therefore, when replenishing fluid, normal blood sodium or elevated blood sodium should also be preferred to saline or compound sodium chloride. After hemodynamic stabilization, 5% glucose can be given. When severe hyperglycemia causes a significant increase in plasma osmolality, 0.45% sodium chloride solution should be given. The rate of rehydration should initially be fast enough to resolve upright hypotension, tachycardia, and to produce adequate urine output within 24 hours. However, for longer duration of illness or chronic dehydration, a rate of about 350 ml/h early on, or 50% of the 12-hour rehydration volume (about 1 L/d in patients without fever), is more appropriate to prevent heart failure. Although this rate of rehydration in the elderly is slow and there is a risk of renal failure, cardiac accidents, and stroke, this method is still safe under adequate supervision. In left ventricular infarction with hypotension, factors causing true fluid loss, such as diuresis and salt restriction, should be excluded first; in sepsis, hypotension is caused by volume deficiency or vascular bed dilatation, and warm limbs often indicate vascular bed dilatation, while cold limb endings indicate blood volume deficiency, which is often very difficult to identify; for extracellular fluid in the distribution of abnormal causes, colloid solution can be supplemented appropriately; when blood pressure returns to normal and After blood pressure is normalized and blood volume is replenished, mannitol can be given for tissue dehydration and osmotic diuresis to facilitate the regression of plasma cavity effusion and edema. Patients with heart failure should be given fluid therapy decisively when low sodium, low potassium, dehydration, acid-base balance disorders, infection, vomiting and diarrhea occur. The daily water intake in mild and moderate heart failure with normal urine output is 1500-2000 ml of physiological minimum requirement, including the water contained in drinking water and food. In refractory heart failure with severe edema, the daily water intake should be within 600ml.