To determine if critically ill patients with acute respiratory failure treated with carbocisteine, hypertonic saline, or both, experience increased hydration of airway mucus.

When people become critically ill, their lungs can sometimes stop working properly. This condition is called acute respiratory failure. Patients with lung failure need urgent treatment in an intensive care unit (ICU) and often rely on a breathing machine (ventilator) to push oxygen into their lungs. While ventilators are life-saving, they make it difficult for patients to clear their airway secretions naturally. Over time, thick, sticky phlegm can build up, blocking the airways and increasing the risk of serious lung infections.

To help solve this problem, doctors sometimes prescribe medicines known as 'mucoactives'. These are designed to loosen and thin out phlegm. This study focuses on two treatments: carbocisteine, which is given as a liquid or powder through a feeding tube, and hypertonic saline, which is a sterile salty water mist breathed in through a mask or breathing tube. A major UK study called MARCH is currently testing whether these medicines help patients recover faster so they can be taken off ventilators sooner.

This study, called EME, works alongside the main MARCH trial. By collecting small samples of airway mucus that are removed during routine ICU care, scientists will test how thick, sticky, and inflamed the phlegm is under different treatments. The goal is to understand the exact biological ways these medicines hydrate and break down mucus. This valuable information will help doctors prescribe the right doses and choose the best future therapies for people fighting life-threatening lung conditions.