Decreased volume of extracellular fluid

The decrease in the volume of the extracellular fluid is a decrease in the volume of the extracellular fluid caused by the loss of water and the total sodium content in the body. Possible causes include vomiting, increased sweating, diarrhea, burns, diuretics, and kidney failure. Clinical manifestations include a decrease in skin turgor, dry mucous membranes, tachycardia, orthostatic hypotension. Diagnosis is based on clinical data. Treatment includes the administration of water and sodium.

[1], [2], [3]

Causes of the reduction of extracellular fluid volume

The decrease in the volume of the extracellular fluid (hypovolemia) does not correspond to a decrease in the volume of the plasma. A decrease in the volume of plasma can be observed with a reduced volume of extracellular fluid, but it also occurs with an increase in the volume of the extracellular fluid (for example, in heart failure, hypoalbuminemia, capillary leakage syndrome). When the volume of the extracellular fluid decreases, a loss of sodium is usually observed; loss of sodium always causes water loss. Depending on many factors, the concentration of sodium in the plasma can be high, low or normal, despite a decrease in the total sodium content in the body.

Extrarenal causes

• Bleeding.
• Dialysis: hemodialysis, peritoneal dialysis.
• Gastrointestinal: vomiting, diarrhea, nasogastric aspiration.
• Skin: increased sweating, burns, exfoliation.
• Fluid retention in spaces: intestinal lumen, intraperitoneal, retroperitoneal.

Renal / adrenal causes

• Acute renal failure: diuresis during recovery.
• Diseases of the adrenal glands: Addison's disease (deficiency of glucocorticoids), hypoaldosteronism.
• The syndrome of Barter.
• Diabetes mellitus with ketoacidosis or high glucosuria.
• Reception of diuretics.
• Soltering kidney diseases (juvenile nephronophthisis, interstitial nephritis, some cases of pyelonephritis and myeloma)

[4], [5], [6], [7], [8]

Symptoms of the reduction of extracellular fluid volume

A decrease in the volume of the extracellular fluid should be suspected in patients with inadequate fluid intake in the anamnesis (especially in a coma or in disoriented patients); with increased fluid loss, treatment with diuretics; kidney or adrenal gland diseases.

With a slight decrease in the volume of the extracellular fluid (5%), the only sign may be a decrease in the skin turgor. The patient can complain of thirst. Dry mucous is not always associated with a decrease in the volume of the extracellular fluid, especially in the elderly or in patients breathing mainly through the mouth. Typical oliguria. With a decrease in the volume of the extracellular fluid by 5-10%, orthostatic tachycardia, hypotension or a combination of them are usually observed, although orthostatic changes can also occur in patients without reducing the volume of the extracellular fluid, especially in weakened patients and bedridden. The skin turgor (better evaluated on the upper part of the trunk) can be lowered. If dehydration exceeds 10%, there may be signs of shock (tachypnea, tachycardia, hypotension, impaired consciousness, poor filling of capillaries).

Diagnostics of the reduction of extracellular fluid volume

Diagnosis is usually based on clinical manifestations. If the cause is obvious and easily amenable to correction (for example, acute gastroenteritis in a otherwise healthy patient), laboratory testing is not necessary; in other cases, the determination of serum electrolytes, blood urea nitrogen and creatinine is necessary. Determination of osmolality of plasma, urine sodium, creatinine and urine osmolality is carried out if there is a suspicion of a clinically significant electrolyte imbalance, which is not detected in the analysis of serum, also in patients with heart and kidney disease. Invasive monitoring is necessary for patients with previous unstable heart failure or arrhythmias.

With a decrease in the volume of the extracellular fluid, central venous pressure and occlusion pressure of the pulmonary arteries are usually reduced, but their measurement is rare.

With a reduction in the volume of the extracellular fluid, normally functioning kidneys retain sodium, so the concentration of sodium in the urine is usually less than 15 meq / l; the sodium excretion fraction (Na urine / Na serum divided by serum creatinine / serum creatinine) is usually less than 1%; osmolality of urine is often more than 450 mOsm / kg. If the decrease in the volume of the extracellular fluid is combined with metabolic alkalosis, the concentration of sodium in the urine can be high; in this case, the concentration of chlorine in the urine is less than 10 meq / l more reliably indicates a reduction in the volume of the extracellular fluid. But a high level of sodium in the urine (usually> 20 meq / L) or low urine osmolality can develop as a result of renal sodium loss in kidney disease, diuretics or adrenal insufficiency. When the volume of the extracellular fluid decreases, the levels of blood urea nitrogen and plasma creatinine are often increased with a blood urea nitrogen to creatinine ratio of more than 20: 1. Such an indicator as hematocrit is often increased with a decrease in the volume of the extracellular fluid, but it is difficult to analyze without the presence of basal values.

[9], [10], [11], [12]

Treatment of the reduction of extracellular fluid volume

Correction of the cause of a decrease in the volume of the extracellular fluid is necessary, as well as the introduction of a liquid to compensate for the existing deficiency of fluid, the continued loss of fluid and the provision of a daily body requirement. In the case of mild or moderate fluid deficiency, it is possible to administer water and sodium by oral route if the patient is conscious and does not suffer from severe vomiting. If there is a significant deficiency of fluid or oral hydration is ineffective, intravenous administration of 0.9% saline is performed.