Continuous Measurement of Diaphragm Excursion as a Predictor of Extubation Failure

Background: Patients are put under invasive mechanical ventilation (MV) during respiratory failure because they can no longer breathe in a way that delivers enough oxygen to their body. MV involves placing a tube into the wind pipe that is attached to a machine (known as a ventilator) which helps the patient breathe. However, MV is associated with complications such as shrinkage and damage of the diaphragm muscle fibres. It has been shown that the diaphragm (the main breathing muscle which provides approximately 70% of the work in healthy persons) can be affected after only 3-4 days of MV. Disconnection from the ventilator (a process known as extubation) is conducted with the calculated risk that the patient may become exhausted due to the additional workload of breathing off the ventilator resulting in needing to be reconnected to the ventilator (a process known as reintubation). Reintubation requires additional deep sedation of the patient and leads to longer time connected to the ventilator, increased risk of new lung infections, prolonged stay in the intensive care unit (ICU) and further immobilisation. Thus, the intensive care physician must constantly evaluate the need for MV to maintain adequate breathing versus withdrawal as quickly as possible to reduce the risk associated with long-term use of MV. However, to date, there is no technique for continuous assessment of diaphragm function that can be easily used at the patient's bedside. RESPINOR DXT, which offers continuous ultrasound monitoring of the right diaphragm velocity without the need of the continued presence of an operator, could offer an interesting solution.

Aim: The primary objective of this study is to compare diaphragm excursion values obtained around a 30-minute SBT using RESPINOR DXT in patients who are successfully and unsuccessfully extubated. Data analysis will be performed using post-processing. The timepoints to be analysed will be:

* Pre-SBT: 10, 30 and 60 minutes before the start of the SBT * During the 30-minute SBT: 0, 1, 2, 3, 4, 10, 20 and 30 minutes * Post-SBT: 5, 10, 20, 30 minutes, 1, 2, 3, 4, 6, 8, 12, 24, 48 hours after the end of the 30-minute SBT.

Hypothesis: The investigators hypothesise that there will be significantly different median diaphragm excursion between successful and failed extubation groups in at least one of the timepoints of interest. The information from this pilot study will be used to design a fully-powered observational study.

Primary outcome: Median diaphragm excursion