40% of all patients in the intensive care unit (ICU) need a ventilator to support their lungs, with many associated complications. Currently the main indication of clinical deterioration is the presence/spreading of shadowing on the chest x- ray. This has many different causes (all requiring different treatments). There is a pressing need for rapid bedside tests to provide definitive diagnostic information about what is happening in the lungs themselves. Many studies have used blood markers, but in patients with multi-system disease these are not specific for the lung and the results are too slow to be useful in the rapidly-changing ICU setting. We will employ cutting-edge technology to pass a tiny optical fibre deep into the lungs of ventilated patients and spray a 'microdose' of an imaging agent that will tell us the reasons for the lung deterioration. This approach has the potential to rapidly determine, at the bedside, if the lung shadowing is due to inflammation. Such an approach could revolutionise the way we deal with the critically ill patient and provide rapid, point of care diagnostics that would help tailor the patient's management.