Hypertonic dehydration refers to a condition characterized by a reduction in extracellular fluid combined with hypernatremia. Its defining features include a greater loss of water relative to sodium, with serum sodium levels exceeding 150 mmol/L and plasma osmolality greater than 310 mOsm/kg H2O. Both extracellular and intracellular fluid volumes decrease, and the condition is also known as hypovolemic hypernatremia.
Etiology
Insufficient water intake is a common cause, often seen in situations such as difficulty with eating or drinking, for example, swallowing difficulties caused by esophageal cancer, or inadequate water provision in critically ill patients.
Excessive water loss can contribute to this condition. High fever, profuse sweating, hyperthyroidism, and extensive burns can lead to significant loss of hypotonic fluids through the skin.
Loss of isotonic or sodium-poor digestive fluids may occur due to vomiting, diarrhea, or gastrointestinal drainage.
Conditions like central or nephrogenic diabetes insipidus can cause the kidneys to excrete large volumes of hypotonic urine. The use of large amounts of diuretics, such as mannitol or glucose, as well as situations like concentrated high-protein tube feeding in comatose patients, can lead to solute-induced diuresis and result in water depletion.
Excessive ventilation, for any reason, may increase insensible water loss through respiratory mucosal evaporation, leading to the loss of water without electrolytes.
Clinical Manifestations
The symptoms of hypertonic dehydration vary depending on the degree of water loss:
- Mild dehydration (water loss equal to 2%–4% of body weight): Symptoms typically involve thirst without other significant abnormalities.
- Moderate dehydration (water loss equal to 4%–6% of body weight): Features include intense thirst, fatigue, reduced urine output, dry lips and tongue, loss of skin elasticity, sunken eyes, restlessness, increased muscle tone, and hyperactive tendon reflexes.
- Severe dehydration: In addition to the above symptoms, patients may exhibit mania, hallucinations, confusion, delirium, seizures, coma, and hypotension, which may progress to death.
Diagnosis
The diagnosis of hypertonic dehydration is supported by a relevant clinical history and symptoms. Laboratory findings typically include:
- Elevated urine specific gravity and increased urine osmolality.
- Mild increases in red blood cell count, hemoglobin concentration, and hematocrit.
- Serum sodium concentration exceeding 150 mmol/L or plasma osmolality greater than 310 mOsm/kg H2O.
Treatment
The primary disease or cause should be addressed while managing sodium intake and correcting extracellular fluid volume abnormalities. In cases with ongoing fluid loss, replacement therapy is indicated. Severe hypernatremia is often managed in two phases:
- The initial phase focuses on rapidly correcting extracellular fluid volume deficits to improve tissue perfusion and resolve shock.
- The subsequent phase involves gradually correcting water deficits, accounting for ongoing water loss.
The required replacement fluid volume is determined based on clinical symptoms as well as the estimated percentage of body weight lost to dehydration. For each 1% loss of body weight, approximately 400–500 mL of fluid is needed. The total water replacement should include both insensible water loss and water losses via urine and the gastrointestinal tract. Patients able to eat and drink may be given fluids orally, while those unable to do so can be treated with intravenous 5% glucose solution.
The correction rate for hypertonic dehydration should not be too rapid, typically limited to 0.5–1.0 mmol/L per hour, to avoid the risk of cerebral edema caused by rapid volume expansion. Monitoring of systemic status and serum sodium levels is essential during treatment, with adjustments to ongoing fluid replacement as needed.
Although total sodium content in the body is reduced in hypertonic dehydration, water loss exceeds sodium loss, resulting in hypernatremia. During the correction of dehydration, limited sodium supplementation may still be required.