Uncontrolled diabetes mellitus is a frequent cause of polyuria from a solute diuresis due to glycosuria. Key findings may include acid-base disturbances, such as non-anion gap metabolic acidosis or metabolic alkalosis, and impaired reabsorption of urinary solutes. The mannitol again draws the water with it, and diuresis (increased urination) ensues. Mannitol may be used to reduce intraocular pressure when given intravenously. The mannitol is a new solute in the intravascular space, which increases the tonicity of the blood plasma Post-obstructive diuresis is an abnormal condition of prolonged polyuria Ref Harrison20th edition pg 299