Etiology: Causes of Water Deficiency
The development of hypohydration is driven by two main groups of factors:
- Inadequate Intake:
- Water deprivation (lack of access to drinking water).
- Neurological disorders that suppress the sensation of thirst (brain injury, ischemia, tumors).
- Somatic obstacles (dysphagia, esophageal obstruction).
- Increased Fluid Loss:
- Renal losses: polyuria in diabetes mellitus or improper use of diuretics.
- Gastrointestinal disorders: intractable vomiting, diarrhea, hypersalivation, fistulas.
- External factors: intense sweating in hot weather or during physical exertion, fever (each degree above normal increases water loss by 400–500 mL).
- Massive blood loss and lymphorrhea (burns, trauma).
Hypoosmolar Hypohydration
This variant develops when electrolyte (salt) loss exceeds water loss. As a result, the osmolarity of the extracellular fluid drops, triggering a pathological process of dyshydration:
- The osmotic pressure inside cells becomes higher than in the interstitium.
- Water rushes from the extracellular space into the cells.
- Outcome: The volume of extracellular fluid decreases sharply, while cells swell.
The key danger of this condition is the absence of thirst because cells are over-saturated with water, masking the true fluid deficit in the body.
Clinical Presentation and Consequences
Symptoms of hypohydration are non-specific, but allow for clinical suspicion upon examination:
- External signs: Skin loses elasticity (turgor), eyes appear sunken, and mucous membranes become dry.
- Hemodynamics: Due to a reduced circulating blood volume (CBV), arterial pressure drops, veins collapse, and tachycardia develops.
- Metabolism: Blood viscosity increases, impairing microcirculation and provoking various types of hypoxia (circulatory, hemic, and tissue hypoxia).