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According to the anatomical proximity of the heart temporarily elevated intrathoracic pressures may have direct and indirect effects on the cardiovascular system. Undesirable hemodynamic effects of a recruitment maneuver primarily arise from the transiently increased airway pressure, manifesting in decreased right heart filling, increased pulmonary vascular resistance, a drop in left ventricular systolic transmural pressure, right and left heart ventricular interactions and subsequent changes in cardiac index. These effects can be more pronounced in patients suffering from ARDS, a condition commonly accompanied by hemodynamic instability. The complex pathophysiological changes account for why routine intensive care monitoring, such as invasive arterial blood pressure or central venous pressure monitoring is insufficient to follow hemodynamic changes under recruitment maneuver.

Previous studies by the same research team confirmed that the alveolar recruitment maneuver improves oxygenation in patients with moderate-to-severe hypoxemic respiratory failure under pressure supported ventilation. Following recruitment maneuver, arterial oxygenation increased in 74 % of all patients. However, there is lack of information regarding the actual degree of changes in transpulmonary pressure and the consequent hemodynamic alterations.

The primary aim of the study is to evaluate precisely the transpulmonary pressure changes during recruitment in patients with severe hypoxemic respiratory failure ventilated in pressure support mode following insertion of a balloon-catheter into the esophagus. In the meantime, hemodynamic changes are monitored by PiCCO and transthoracic echocardiography, and lung field aeration by electric impedance tomography.

Inclusion Criteria:

• orotracheal intubation
• pressure supported ventilation
• moderate-to-severe hypoxemic respiratory failure according to ARDS Berlin Criteria Moderate: 100 Hgmm ≤ PaO2/FiO2 ≤ 200 Hgmm, PEEP ≥ 5 cmH2O Severe: PaO2/FiO2 ≤ 100 Hgmm, PEEP ≥ 5 cmH2O

Exclusion Criteria:

• age < 18 years
• pregnancy
• previous pulmonary resection, pulmonectomy
• clinically verified, end-stage COPD
• severe hemodynamic instability (i.e. refractory shock to vasopressors)
• severe emphysema and/or spontaneous pneumothorax in past medical history
• contraindications of a balloon-catheter (e.g. esophageal abscess, esophageal perforation, esophageal diverticulosis, esophagus tumor, esophagus varix, recent esophagus or gastric surgery, severe coagulopathy)