What is saline and why is it used in respiratory illnesses?

Saline solution has a wide range of uses in medicine and is a common sight everywhere from hospitals to home medicine cabinets, but what exactly is it and what specific applications does it have? In this post, we take an in-depth look at the substance and explore the various purposes it can serve.

What is saline?

Saline solution is simply a combination of water and sodium chloride (NaCl), or salt. NaCl can be made in a lab by reacting chlorine with sodium, but it’s also found naturally in large quantities in underground deposits and in seawater.

Saline is available in a range of different concentrations to suit various uses. With a concentration of 0.9% salt, it is often referred to as normal saline or “isotonic” saline. In higher concentrations (of 3% & 6%), saline is described as ‘hypertonic’. This type of solution was first described by Dutch physiological chemist Dr Hartold Hamburber in the 1890s, who discovered it had a similar freezing point to human serum. Serum is the fluid in blood that remains once clotting factors are removed.

What does saline do?

Different concentrations of saline all appear as a clear liquid, just like water, but they have very different physiological effects and are therefore used in different ways.

What is saline solution used for?

Normal saline can be used for everything from cleaning wounds to gargling. This is because its properties can help to prevent infection and promote healing, and it is relatively inexpensive and readily available. This liquid is also commonly used to rinse contact lenses and as eye drops, as it has it has roughly the same concentration of salt as tears. Another widely used application of this type of fluid is intravenous therapy. When patients are dehydrated and they are struggling to take fluids by mouth, isotonic saline can be administered via a drip. The NHS states that it is indicated for use in restoring the loss of body fluids and in conjunction with blood transfusions.

This type of solution is commonly used to gargle with as it helps to relieve sore throats. Isotonic saline can be used as a nasal wash too. When flushed through the nose, it can help to wash away allergens such as pollen and dust, and it can also clear mucus and other debris. Nasal irrigation like this can help to relieve the symptoms of congestion and prevent infections of the sinuses.

Another way to use isotonic saline is to mix it with certain medications to create a liquid suitable for inhaling using a nebuliser.

In contrast, hypertonic saline is often inhaled as a nebulised treatment itself. It is recommended for many people with a range of respiratory conditions, such as bronchiectasis, chronic obstructive pulmonary disease (COPD) and cystic fibrosis.

Why is saline used in respiratory illnesses?

The reason why hypertonic saline is widely used as a treatment for respiratory conditions is because it is a ‘mucoactive agent’, meaning it can help to clear mucus and sputum from the airways, including the lungs, trachea and bronchi. It does this by increasing the amount of salt in the airways. This salt then attracts water, which helps to thin mucus and sputum, making it easier for patients to cough it up. In turn, this can help people to breathe more freely and it also reduces the risk of infections.

Research backs up the benefits of hypertonic saline as a treatment for various lung conditions. For example, a long-term randomised controlled trial published in the New England Journal of Medicine showed improvements in lung function and a reduction in instances of antibiotic use in people with cystic fibrosis using hypertonic saline compared to people using isotonic saline¹. Because of its effectiveness, the American Cystic Fibrosis Foundation and the current UK clinical guidelines recommend hypertonic saline as part of a treatment regimen for this medical condition. 

As with any new treatment, it is important to seek advice from your doctor before trying it out.

Hypertonic saline is used with a nebuliser, which changes the liquid into a fine mist that patients can inhale using either a mouthpiece or a mask. This helps ensure it goes directly to the lungs where it is needed.