Measurements of esophageal pressure (Pes) as surrogate for pleural pressure are routinely performed in selected ICU patients to facilitate lung-protective ventilation and assess breathing effort. Pes is clinically measured via a nasogastric esophageal catheter. Current techniques involve balloon catheters but have some important disadvantages as they could deflate over time and require a very precise positioning and filling volume. A solid-state sensor does not have disadvantages associated with balloon catheters and may therefore be a useful alternative in clinical practice.

This method-comparison study in adult mechanically ventilated ICU patients evaluates the accuracy of Pes measured using an esophageal catheter with a solid-state sensor as compared to a balloon catheter as reference standard.

Measurements of esophageal pressure (Pes) as surrogate for pleural pressure are routinely performed in selected ICU patients to facilitate lung-protective ventilation and assess breathing effort. Pes is clinically measured via a nasogastric esophageal catheter. Current techniques involve balloon catheters but have some important disadvantages as they could deflate over time and require a very precise positioning and filling volume. A solid state sensor does not have disadvantages associated with balloon catheters and may therefore be a useful alternative in clinical practice.

This method-comparison study in adult mechanically ventilated ICU patients evaluates the accuracy of Pes measured using an esophageal catheter with a solid-state sensor as compared to a balloon catheter as reference standard.

Subjects will receive a standard balloon esophageal catheter and a solid-state pressure catheter for simultaneous measurements of Pes. Study population will be post-surgical ICU patients. Measurements will be performed during clinical mechanical ventilation settings which include a first phase of passive controlled ventilation (patient is still sedated after surgery) as well a phase of partially-assisted ventilation where the patient's breathing effort has resumed and is assisted by the ventilator. During both phases, 10-15 minutes of tidal breathing will be recorded.

Inclusion Criteria:

• Signed informed consent
• Patient requiring mechanical ventilation at the ICU following cardiothoracic or abdominal surgery
• Age ≥ 18 year

Exclusion Criteria:

• Pregnancy
• Upper airway/esophageal/mouth or face pathology (i.e. recent surgery, esophageal varices, diaphragmatic hernia)
• Nasal bleeding within the last <2 weeks
• Presence of pneumothorax
• Use of anticoagulants that increase the risk of catheter insertion