Mannitol is an osmotic diuretic that is a six-carbon carbohydrate that undergoes filtration at the glomerulus with limited or no reabsorption in the proximal tubules. It works as osmotic diuretic and is often used to reduce intracranial pressure and treat oliguric renal failure. At large doses mannitol increases excretion of sodium and potassium.
Initially, mannitol acutely raises plasma and extracellular osmolality, which leads to an increase in circulating blood volume. This leads to increase in stroke volume, cardiac output, and blood pressure. In patients unable to compensate for the increase in circulating blood volume, pulmonary edema and other signs and symptoms of congestive heart failure may result. Following diuresis, patients may be slightly hypovolemic with associated decreases cardiac output and blood pressure. Hypokalemia and hypernatremia may also occurs. Hypernatremia is due to excess loss of water compared to sodium. High doses of mannitol can also be nephrotoxic (increased risk in patients with prior renal insufficiency.
- Nikki Sabharwal, G S Umamaheswara Rao, Zulfiqar Ali, Muthuchellappan Radhakrishnan Hemodynamic changes after administration of mannitol measured by a noninvasive cardiac output monitor. J Neurosurg Anesthesiol: 2009, 21(3);248-52