Water and sodium are lost simultaneously, but the water loss exceeds the sodium loss, resulting in serum sodium levels higher than the normal range and a hypertonic state in the extracellular fluid. When water loss surpasses sodium loss, the osmotic pressure of the extracellular fluid increases, leading to enhanced secretion of antidiuretic hormone and greater water reabsorption by the renal tubules, which reduces urine output. Aldosterone secretion also increases, promoting the reabsorption of both sodium and water to maintain blood volume. If the water deficit continues, the osmotic pressure of the extracellular fluid rises further, causing intracellular fluid to shift outward. Ultimately, the degree of intracellular water deficit exceeds that of the extracellular fluid. Dehydration of brain cells can lead to impaired brain function.

bubble_chart Etiology

Mainly include: a. Insufficient water intake, such as trauma, unconsciousness, difficulty swallowing due to esophageal diseases, inability to eat, inadequate water supply for critically ill patients, nasogastric feeding of hypertonic diets, or infusion of large amounts of hypertonic saline solution, etc.; b. Excessive water loss without timely replenishment, such as high fever, profuse sweating, extensive burns, tracheotomy, prolonged exposure of internal organs during thoracic or abdominal surgery, diabetic unconsciousness, etc.

bubble_chart Clinical Manifestations

Depending on the symptoms, hypertonic dehydration is generally divided into grade III:

Grade I dehydration: Apart from thirst, there are usually no other symptoms. The water deficit is 2-4% of body weight.

Grade II dehydration: There is extreme thirst, accompanied by lack of strength, oliguria, and high urine specific gravity. Dry lips and tongue, poor skin elasticity, sunken eye sockets, and frequent irritability. The water deficit is 4-6% of body weight.

bubble_chart Diagnosis

The diagnosis can generally be made based on medical history and clinical manifestations. Laboratory findings include: a. high urine specific gravity; b. elevated serum sodium, often above 150 mmol/L; c. grade I increases in red blood cell count, hemoglobin, and hematocrit.

bubble_chart Treatment Measures

Remove the disease cause to prevent further fluid loss in the patient. Replenish the lost fluids by intravenous infusion of 5% glucose or hypotonic saline solution. There are two methods to estimate the amount of fluid loss to be replenished: a. Estimate based on the severity of clinical manifestations and the percentage of body weight lost. For example, grade II dehydration corresponds to a fluid loss of 4–6% of body weight, with a replenishment volume of approximately 2.5L–3.0L. b. Calculate based on the measured blood Na⁺ concentration.

Water replenishment volume (ml) = [Measured blood sodium value (mmol) - Normal blood sodium value (mmol)] × Body weight (kg) × 4.

For example, a 60kg male with sexually transmitted disease has a blood sodium concentration of 152mmol/L. The water replenishment volume would be (152 - 142) × 60 × 4 = 2.4L. On the first day, administer half of the calculated volume (1.2L), with the remaining half given the next day. Additionally, the daily required volume should also be replenished.

During fluid replenishment, note that although blood Na⁺ levels are elevated, the actual total sodium content in the body is reduced due to dehydration and hemoconcentration. Therefore, sodium should be appropriately supplemented alongside water to correct sodium deficiency. If potassium deficiency also requires correction, potassium supplementation should begin only after urine output exceeds 40ml/h to avoid hyperkalemia. If metabolic acidosis persists after fluid therapy, sodium bicarbonate solution may be administered.