What is the pathophysiological result of a free water deficit?

A free water deficit occurs when there is a loss of water without a corresponding loss of solute. This can happen due to various causes such as dehydration, excessive sweating, or conditions that lead to increased urine output without adequate fluid intake. When there is a deficit of free water, the concentration of sodium in the serum increases because the volume of water in the body decreases while the total amount of sodium remains the same, leading to hypernatremia.

Hypernatremia is characterized by elevated sodium levels in the blood (usually defined as serum sodium greater than 145 mEq/L). This increase in sodium concentration results from the insufficient fluid to dilute the sodium, which can cause a range of symptoms from mild neurological disturbances to more severe complications like seizures or coma in extreme cases. Therefore, the pathophysiological consequence of a free water deficit is primarily the development of hypernatremia.