Hypertonic saline (3% NaCl as opposed to 0.9% isotonic NaCl/Normal Saline) is used to treat cerebral oedema, explain how does it work

Hypertonic saline works to treat cerebral edema through the following steps:

1. Osmosis: Hypertonic saline has a higher concentration of solutes (in this case, sodium chloride or NaCl) than the cells in the brain. According to the principle of osmosis, water tends to move from an area of lower solute concentration to an area of higher solute concentration to achieve equilibrium.

2. Dehydration of cells: When hypertonic saline is administered, it creates a high solute concentration in the blood. This causes water to move out from the brain cells (which are swollen due to edema) into the bloodstream, in an attempt to balance the solute concentration. This process dehydrates the cells and reduces their swelling.

3. Increased blood volume and pressure: The movement of water into the bloodstream increases the blood volume and pressure. This helps in improving the blood flow in the brain, which can be compromised due to the swelling.

4. Removal of excess fluid: The kidneys play a crucial role in maintaining the body's fluid balance. The increased blood volume due to the movement of water from the brain cells to the bloodstream triggers the kidneys to remove the excess fluid from the body through urine.

5. Reduction in brain swelling: As the excess water moves out from the brain cells and is eventually excreted by the kidneys, the swelling in the brain reduces. This relieves the pressure on the brain, improving its function and reducing the symptoms of cerebral edema.

In summary, hypertonic saline works by using the principles of osmosis and fluid balance to draw water out of swollen brain cells, thereby reducing cerebral edema.