The study protocol consisted of two consecutive parts. In the first part (step one), the patients were deeply sedated and paralyzed. The anesthesia was maintained with infusion of propofol 1 % (200–300 γ/Kg/min) and paralysis with rocuronium (a bolus of 0.8 mg/kg at the begin and subsequently 20 mg every 20 min) to obtain a total myorelaxation. Sedation was titrated to obtain a state equivalent to a Richmond Agitation Sedation Score (RASS) of −5. A tidal volume of 6–8 ml/Kg of predicted body weight was applied during volume-controlled ventilation.
Subsequently in the second part (step two), after about 60 min from the end of the first part, patients were maintained sedated without paralysis and ventilated in pressure support ventilation to insure a tidal volume similar to that of volume-controlled ventilation. Sedation was titrated to obtain a RASS between −3 and −2. Patients were always maintained in supine position at 0° for the entire study. Because the most of the patients were enrolled in intensive care unit after elective general anesthesia (i.e., already sedated and paralyzed), the first and the second parts of the study were not performed in a random fashion and the sedation and paralysis step was always done first. However, the measurements collected in the four different study conditions both during controlled and pressure support ventilation were taken in a random fashion as follows:1 .![]()
Subsequently in the second part (step two), after about 60 min from the end of the first part, patients were maintained sedated without paralysis and ventilated in pressure support ventilation to insure a tidal volume similar to that of volume-controlled ventilation. Sedation was titrated to obtain a RASS between −3 and −2. Patients were always maintained in supine position at 0° for the entire study. Because the most of the patients were enrolled in intensive care unit after elective general anesthesia (i.e., already sedated and paralyzed), the first and the second parts of the study were not performed in a random fashion and the sedation and paralysis step was always done first. However, the measurements collected in the four different study conditions both during controlled and pressure support ventilation were taken in a random fashion as follows:
PEEP 0 cmH2O with esophageal balloon placed at 25–30 cm from the mouth (middle position)
PEEP 0 cmH2O with esophageal balloon placed at 40–45 cm from the mouth (low position)
PEEP 10 cmH2O with esophageal balloon placed at 25-30 cm from the mouth (middle position)
PEEP 10 cmH2O with esophageal balloon placed at 40–45 cm from the mouth (low position)
Schematic overview of the study protocol
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