Basic and Clinical Sciences (BCSE) 2025 – 400 Free Practice Questions to Pass the Exam

The primary cause of hypervolemic hypernatremia is the gain of salt and water, with the increase in salt being greater than the increase in water. In this condition, the body's total volume is elevated because of the excess sodium, which leads to an increase in the osmolality of the extracellular fluid.

When more salt is gained than water, it results in hypernatremia because sodium levels rise due to the increased concentration from the relatively lower amount of water. This situation can occur in various clinical contexts such as excessive salt intake combined with an inadequate water intake or in cases of certain disorders that lead to an increase in both sodium and water retention, but with a predominant effect from the sodium.

In contrast, loss of both water and sodium would not produce hypervolemic hypernatremia; rather, it would lead to normovolemic or hypovolemic states. Pure water loss primarily results in hypernatremia without an associated increase in volume. Increased water retention with normal sodium levels would not lead to hypernatremia but rather a dilution of sodium levels. Hence, the specific interplay of greater sodium gain relative to water gain is what defines hypervolemic hypernatremia.