Which of the following conditions is an example of hypovolemic hypotonic hyponatremia?

Hypovolemic hypotonic hyponatremia occurs when there is a deficit of total body sodium along with an excess of total body water, which ultimately dilutes serum sodium levels. Excessive sweating is a classic example of this condition because it results in the loss of salt and water. When individuals sweat profusely, they typically lose more sodium relative to water, leading to a reduced serum sodium concentration while the total body water is either retained or increased due to compensatory mechanisms.

In contrast, the other options represent different pathophysiological mechanisms. Congestive heart failure (CHF) typically leads to a state of euvolemic or hypervolemic hyponatremia due to increased water retention from heart insufficiency and subsequent dilution of serum sodium. The syndrome of inappropriate antidiuretic hormone secretion (SIADH) often causes euvolemic hyponatremia, where total body water increases without a corresponding increase in sodium, while renal failure can also cause a mix of volume status that may not pertain directly to hypovolemic hypotonic type. Thus, excessive sweating stands out as the main cause of hypovolemic hypotonic hyponatremia, validating that choice as the correct