Fig. 1
Schematic representation of the study protocol. CV1 first period of lung protective conventional ventilation, PEEP positive end-expiratory pressure, TEE transesophageal echocardiography, SM safety measurement, RVEDA right ventricular end-diastolic area, LVEDA left ventricular end-diastolic area, FiO2 inspiratory oxygen fraction, RM recruitment maneuver, mPaw mean airway pressure, SpO2 peripheral oxygen saturation, HFO high-frequency oscillation, TGI tracheal gas insufflation, CV2 second (study protocol concluding) period of lung-protective conventional ventilation. *Continuous positive airway pressure of 45 cmH2O for 40 s; the HFO breathing circuit was pressurized with the oscillator piston off. †During the first study TEE SM (measurement duration, < 5 min), an RVEDA/LVDEA ratio of > 0.8 triggered a PEEP decrease by 2–3 cmH2O. ‡Performed within 15–20 min after a protocol-mandated decrease in PEEP (see above); this (second) TEE SM was not performed whenever RVEDA/LVEDA did not exceed 0.8 at the first TEE SM. §Includes saved midesophageal four-chamber views and, transgastric, two-chamber, short-axis views, and hemodynamic and gas exchange data during all ventilator strategy testing periods; quasistatic respiratory compliance data were also obtained during CV1 and CV2; each time, the study protocol measurements were to be completed within 10 min. ║During HFO-TGI, the mPaw was set at 2–3 cmH2O lower than the “study HFO mPaw” to counterbalance an estimated, TGI-associated increase of similar magnitude in HFO tracheal pressure; see also text, reference [15] and Additional file 1