34.3 Osmotic Diuretics

Introduction and Use

Mannitol is a large sugar molecule that is readily filtered by the glomeruli and is not reabsorbed by the tubules. The resulting osmotic force increases the loss of sodium and water. Although mannitol is also approved to promote diuresis for acute renal failure and for excretion of toxic substances, it is used most commonly to treat increased intracranial pressure and increased intraocular pressure (Tenny et al., 2022). Mannitol reduces intracranial and intraocular pressures by moving water from the cells into the circulation. In the brain, mannitol creates an osmotic gradient that draws water across the blood–brain barrier. In the eye, mannitol draws water from the vitreous humor into the circulation, which decreases the pressure on the retina. Mannitol therapy requires close monitoring because of the risks for fluid volume excess, electrolyte imbalances, and adverse renal and neurologic effects of increased osmotic pressure.

Hypertonic saline solutions may be used in place of mannitol therapy because the saline solution does not cause hypovolemia in critically ill clients who may already be hypovolemic, hypotensive, or actively bleeding. There is some evidence that hypertonic saline solutions also improve cerebral perfusion and cellular oxygenation (Shi et al., 2020). In addition, in contrast to mannitol, the saline solution can be infused temporarily through a peripheral vein until central venous access is available, and it does not require special reconstitution or delivery systems. Moreover, the therapies are associated with similar clinical outcomes.

Adverse Effects and Contraindications

Mannitol, like other diuretics, can cause electrolyte abnormalities and dehydration. It can cause heart failure secondary to the rapid fluid shift of water into the intravascular space. Administration of the drug has also been associated with the development of AKI in clients with normal renal function. If warm temperatures are not maintained during administration, mannitol can precipitate into crystals, causing vascular and end-organ damage. It is also possible for leakage of mannitol across the blood–brain barrier to cause a rebound increase in intracranial pressure (Tenny et al., 2022).

The client’s kidney function must be adequate to manage the increased diuresis that mannitol will produce. It should be avoided in clients with anuria or previous renal damage caused by mannitol, and it should be used with caution in clients with decreased renal function. It should not be used for clients who are severely dehydrated or who have existing electrolyte abnormalities that could be exacerbated by its administration. Mannitol should not be used in clients with congestive heart failure or pulmonary edema.

Table 34.4 is a drug prototype table for osmotic diuretics featuring mannitol. It lists drug class, mechanism of action, adult dosage, indications, therapeutic effects, drug and food interactions, adverse effects, and contraindications.

Nursing Implications

The nurse should do the following for clients who are taking mannitol:

• Administer the medication through a dedicated IV line in a large central vein (DailyMed, Mannitol, 2023).
• Use only filtered tubing to administer the medication (DailyMed, Mannitol, 2023).
• Avoid administering mannitol simultaneously with blood products.
• Check the medication vial for the presence of crystals. If they are present, warm the solution to 140ºF, vigorously agitate the vial, and then cool the medication to body temperature before administering (DailyMed, Mannitol, 2023).
• Monitor the infusion site for signs of extravasation during administration.
• Carefully monitor the client’s fluid volume status by assessing vital signs and weight.
• Monitor lung sounds for congestion and other signs of heart failure or circulatory overload.
• Monitor laboratory values for electrolyte imbalances.
• Provide client teaching regarding the drug and when to call the health care provider. See below for client teaching guidelines.