Hospitals use saline solutions instead of distilled water for patient care due to fundamental differences in their composition and how they interact with the human body. This distinction is important for patient safety and effective medical treatments.
Understanding Medical-Grade Water
Saline solution, commonly known as normal saline, is a mixture of sodium chloride (salt) and water. It contains 0.9% sodium chloride by weight, meaning 9 grams of salt are dissolved in every 1000 milliliters of water. This precise concentration is important for its medical applications.
Distilled water undergoes a purification process involving boiling and condensing steam. This process removes impurities, dissolved minerals, salts, and other compounds, leaving behind nearly pure H₂O. Distilled water contains almost no ionic impurities and has a neutral pH.
The Principle of Osmosis
Osmosis is a process where water molecules move across a semi-permeable membrane. This movement occurs from an area with a higher concentration of water molecules to an area with a lower concentration of water molecules. This movement continues until the concentration of dissolved substances is balanced on both sides of the membrane.
The cell membranes in the human body, including those of red blood cells, are semi-permeable. Solutions are categorized based on their concentration of dissolved substances relative to the inside of a human cell. An isotonic solution has a similar concentration of solutes as the cell’s internal environment, leading to no net movement of water across the membrane.
In contrast, a hypotonic solution has a lower concentration of solutes than the cell, causing water to move into the cell. Conversely, a hypertonic solution has a higher concentration of solutes than the cell, which draws water out of the cell.
The Danger of Distilled Water for the Human Body
When distilled water is introduced into the human body, it acts as a hypotonic solution. This means it has a significantly lower concentration of dissolved solutes compared to the fluids inside human cells. Due to osmosis, water molecules rapidly move from the distilled water into the body’s cells, including red blood cells.
This influx of water causes the cells to swell. Human cells, including red blood cells, lack a rigid cell wall and cannot withstand excessive swelling, leading to their rupture, a process known as hemolysis.
Hemolysis releases the contents of the red blood cells, including hemoglobin, into the bloodstream. This can lead to complications like kidney damage or failure, as the kidneys struggle to process the free hemoglobin. Electrolyte imbalances can also occur.
Why Saline is the Medical Standard
Normal saline, with its 0.9% sodium chloride concentration, is considered isotonic to human blood and body fluids. This means that when infused into the body, it has a similar solute concentration to the cells, preventing the net movement of water into or out of the cells. As a result, cells, especially red blood cells, maintain their normal size and function.
This compatibility makes saline a versatile and safe fluid for numerous medical applications. It is used for rehydration, particularly in cases of hypovolemia. Saline also serves as a carrier for delivering intravenous medications.
Saline is also used for wound cleaning and irrigation because its isotonic nature prevents damage to delicate tissues. It helps maintain fluid balance in patients unable to take fluids by mouth, making it a standard solution in hospitals.