Dehydration – colloquially called fluid deficiency or dehydration – (synonyms: Dehydration; decrease in body fluid; dehydration; dehydration; dehydration; hypohydration; ICD-10-GM E86: volume deficiency) describes an excessive decrease in body fluid or body water, caused by a pathological (pathological) decreased fluid intake or increased fluid losses. The adult body consists of 60-70% water. Physiologically, more water, about three quarters of the water, is in the intracellular space (inside the cells), the rest circulates extracellularly (outside the cells; interstitial fluid and blood component). Water is a prerequisite for numerous metabolic processes:
- Solvent and transport agent
- Structural component of proteins and polysaccharides (complex carbohydrates/multiple sugars).
- Substrate (starting material) of enzymatic reactions or is their end product.
- Essential (vital) for the acid-base and electrolyte balance – each transport of osmotically active electrolytes is associated with a movement of water
- Excretory and detoxification functions (excretion and detoxification functions) of the kidneys.
- Protection against dropping body temperature as well as overheating.
Water contains various electrolytes (blood salts) in certain concentrations. The main electrolytes include sodium, potassium, calcium and magnesium. As a rule, a loss of body fluid is also accompanied by a disturbance of the electrolyte balance (salt balance).Since water is also the main component of the blood, the viscosity of the blood increases in the absence of water. As a result, the entire body is less well supplied, and brain performance and the ability to concentrate decline. Body water is therefore of great importance. Dehydration can be classified into three forms depending on serum osmolality* , which usually correlates with serum sodium concentration:
- Isotonic dehydration – e.g., due to vomiting, diarrhea (diarrhea).
- Water loss = sodium loss → extracellular water and sodium loss in isotonic ratio (the body loses water and sodium in equal amounts).
- Hypotonic dehydration – e.g., when sweating profusely and water is compensated by low-sodium (“low-salt”) fluid.
- Sodium loss > water loss → too few sodium ions are present in the extracellular space relative to the water present (hyponatremia (sodium deficiency)); consequently, water flows into the intracellular space (into the cells) (extracellular dehydration); as a result, the extracellular space becomes smaller and the cells become overhydrated (intracellular edema formation)
- Hypertonic dehydration – e.g. in fever, excessive sweating without water compensation.
- Water loss > sodium loss → in the extracellular space, the sodium concentration increases (hypernatremia (excess sodium)); consequently, water flows out of the cells into the extracellular space; however, this process is not sufficient to replace the water or to correct the sodium concentration in the extracellular space; finally, there is a deficit of free water with a decrease in extracellular and intracellular volume (relatively higher intracellular water deficit)
* Osmolality is the sum of the molar concentration of all osmotically active particles per kilogram of solvent.These osmotically active substances include mainly calcium, chloride, glucose, urea, potassium, magnesium and sodium. Thus, physiological serum osmolality depends almost exclusively on sodium concentration, since osmotically active changes in the other electrolytes are not compatible with life. Isotonic and hypotonic dehydration are accompanied by hyponatremia (sodium deficiency, < 135 mmol/l), and hypertonic dehydration is accompanied by hypernatremia (sodium excess, > 145 mmol/l). As a result of dehydration, exsiccosis, i.e., dehydration of the body, occurs. Course and prognosis: Water deficiency harms the human organism in many ways. For example, mild dehydration is manifested by thirst and concentrated urine (distinctly colored urine). Moderate dehydration is accompanied by, among other things, tachycardia (excessively fast heartbeat: > 100 beats per minute). Massive dehydration results in standing skin folds and hypotension (low blood pressure).If dehydration is not counteracted in time, there is a risk of shock (acute circulatory failure) with the signs of impaired consciousness (lethargy, delirious states (confusion)) and circulatory insufficiency (circulatory weakness).If dehydration is suspected in infants and the elderly, a doctor must be consulted at an early stage. Infants and young children in particular tolerate a lack of water considerably worse than adults.
