Virna Ignacio Almuete, RPh


October 13, 2005


Is there any circumstance in which hypotonic solutions such as 0.25% sodium chloride may be administered as a hydration fluid?

Response from Virna Ignacio Almuete, RPh

In general, 0.25% saline is rarely used as a hydration fluid by itself. Because of the tonicity gradient, free water would enter the red blood cells, causing them to swell. This could lead to cell lysis.

However, in the setting of sickle cell disease (SCD), 0.25% saline may be used as a hydration fluid without any additives.

The hallmark of SCD is the polymerization of deoxygenated sickle hemoglobin, which results in the distorted shape of red blood cells. The sickling of erythrocytes is dependent on the intracellular concentration of hemoglobin. Higher hemoglobin concentrations lead to sickling of the red blood cells.

When patients with SCD become ill, they often decrease their intake of fluids, leading to dehydration or a decrease of free water. The osmolarity of the plasma increases, which causes dehydration of the red blood cell and results in an increase of mean corpuscular hemoglobin concentration (MCHC), leading to increased sickling of the cell.

Patients are encouraged to consume fluids orally. If they are unable to maintain adequate hydration orally, 5% dextrose or 5% dextrose in 0.25% normal saline solution may be infused. Hypotonic solutions are useful because free water enters the hypertonic red blood cells, leading to a decreased hemoglobin concentration (MCHC) and reduced red blood cell sickling.[1,2]