Severe mannitol-induced hyponatremia complicating transurethral prostatic resection.

A case is presented in which the absorption of mannitol irrigation solution across prostatic veins resulted in severe hyponatremia in a patient undergoing transurethral prostatic resection. Since hyposmolality of the extracellular fluid was not seen because of the presence of mannitol the patient was asymptomatic despite a rapid decrease in the serum sodium concentration to 99 mEq./l. The importance of distinguishing dilutional hyponatremia from hyponatremia with normal or elevated osmolality is discussed.