Hypertonic dehydration means that both water and sodium are lost, but there is more water deficiency than sodium deficiency, so the serum sodium is higher than the normal range and the extracellular fluid is hypertonic, also known as primary dehydration. When there is more water deficiency than sodium deficiency, the osmolarity of extracellular fluid increases, the secretion of antidiuretic hormone increases, the reabsorption of water by the renal tubules increases, and the urine volume decreases. Aldosterone secretion increases, and sodium and water reabsorption increases to maintain blood volume. If the dehydration continues, the osmolarity of extracellular fluid increases further, intracellular fluid moves to the extracellular, and the degree of intracellular dehydration exceeds the degree of extracellular fluid dehydration, which can eventually lead to brain cell dehydration will cause brain dysfunction. Why does hypertonic dehydration result in low central venous pressure? When dehydration occurs, it can cause a series of symptoms of central nervous system dysfunction, including drowsiness, muscle twitching, coma, and even death. When brain volume is significantly reduced due to dehydration, the vascular tension between the skull and cerebral cortex increases, which can lead to low venous pressure.