A Comparative study of airway pressures generated by non-invasive respiratory support used in cardiac surgical patients

Patients undergoing cardiac surgery will be invited pre-operatively to participate in this study. Participants will have pressure measurements carried out with both Optiflow trademark and facemask non-invasive ventilation (NIV). Following surgery, whilst the participant is sedated and ventilated in the Intensive Care Unit, a 10F catheter will be inserted into the nasopharynx via the nose. Once the patient has been woken and extubated a baseline airway pressure measurement will be performed while the patient breathes spontaneously on their routine oxygen therapy device e.g. standard nasal cannulae or facemask. Pressure measurements will be carried out following a random sequence for both the Optiflow trademark system and NIV delivered via a facemask. Participants will have 3 measurements performed on the Optiflow interface at 30, 40 and 50 litres per minute and 3 measurements performed on NIV at 4,6 and 8 cmH2O via a facemask. For each group, pressure measurement for each flow/pressure will be recorded over one minute of breathing using precision pressure transducer (PPT). This procedure is expected to take around 30 mins. The catheter will be removed at the end of this period.