Supplementary Material, 1.
Details about anesthetic management and intraoperative mechanical ventilation strategy.
Anesthetic management was standardized. Patients received no premedication. In the operating room patients were placed in reverse trendelemburg (RTDL) position (30º). Afive-lead electrocardiograph and apulse oximeter (S/5 monitor; Datex-Engstrom, Helsinki,Finland), were placed and a intravenous crystalloid infusion was initiated. Continuous positive airway pressure (CPAP) at 10 cmH2O was applied to all patients during the administration of oxygen in air (FiO2 0.8) for 5 minutesusing a facemask (Ambu Ultraseal; Ambu Inc. USA)fitted tightly to the face to prevent air leaks. After preoxygenation anesthesia was induced with propofol, 3 mg.kg-1 based on ideal body weight (IBW= X + 0.91* height (cm) - 152,4-1; X = 50 for men; X= 45 for women) and fentanyl 1,0 microg.kg-1 IV, followed by rocuronium 0.6 mg. kg-1IV (IBW). Then all the patients were ventilated using pressure support ventilation (PSV) with a inspiratory pressure over PEEPof 10 cmH2O, a PEEP level of 10 cmH2O and a minimum respiratory rate of 10 breaths.min-1 (Engström CareStation, GE Healthcare, Finland). The inspiratory trigger sensitivity was set at itsminimal value to detect inspiratory effort whileavoiding autotriggering and FiO2was kept in 0,8.When neuromuscular blockade was complete tracheal intubation was performed maintaining the RTDL position at 30º. A radial artery was cannulated (Arteriofix art.Kath. B. Braun Medical, Melsungen, Germany) for continuous monitoring of arterial blood pressure and arterial blood gas measurements. Neuromuscular blockade was maintained with rocuronium, with supplemental doses administered to maintain a T1 to T4 ratio of 2/4 (TOF Watch, Bluestar Enterprises, Inc., Chanhassen, MN).Anesthesia was maintained using a continuous infusion of propofol to target a bispectral index ™ (XP version 3.0, Aspect Medical Inc. Norwood, MA) between 40 and 50.Remifentanil was administered at an initial rate of 0.2 microg.kg-1.min_1 (IBW) and adjusted to maintain the blood pressure and heart rate within 20% of the preoperative value. Normothermia was maintained intraoperatively using a forced warm air system (Bair Hugger®, Arizant Healthcare Inc., Eden Prairie, MN). Pneumoperitoneum was achieved by insufflation of carbon dioxide into the peritoneum to reach an intra-abdominal pressure up to 15 mmHg. At the end of surgery, pneumoperitonium was released, propofol and remifentanil were discontinued, morphine sulfate, 50 microg/kg IV (IBW), was administered and residual neuromuscular blockade was reversed with neostigmine, 0.05 mg.kg-1 IV (IBW) and atropine, 0.005 mg.kg-1 IV (IBW)
Intraoperative mechanical ventilation was the same for both groups of patients. The lungs were ventilated with volume-controlled ventilation (VCV) with a mixture of 50% oxygen in air, and a tidal volume of 6 mL.kg-1 (IBW), inspiratory to expiratory ratio 1:2, and PEEP 10 cmH2O. Respiratory rate was adjusted to maintain end-tidal carbon dioxide partial pressure (etCO2) between 30 and 35 mmHg (Ventilator Engström CS, GE Healthcare, Finland). An alveolar recruitment strategy (ARS) was applied after the onset of pneumoperitoneum. ARS was performed by increasing PEEP in steps of 5 cmH2O from 0 to 20 cmH2O using pressure controlled ventilation (PCV) with a driving pressure equal to the airways plateau pressure obtained during VCV. Once PEEP reached 20 cmH2O the driving pressure was augmented to reach 45 cmH2O. After 10 breaths at maximal airways pressure, PEEP was decreased in steps of 2 cmH2O and static compliance of the respiratory system was measured at each step in order to determine the lung's closing pressure. Then a second ARS was applied and PEEP was set at 2 cmH2O higher than the closing pressure. At the end of surgery a new ARS was applied, before the extubation. In this case PEEP after the ARS was kept in 10 cmH2O until the extubation.