Intraoperative Protective Ventilation for Obese Patients Undergoing Gynaecological Laparoscopic Surgery (Inprove4large)

Experimental: Protective ventilation

Volume controlled ventilation with tidal volume 6-7 ml/kg of predicted body weight (45.5 + 0.91 (height [cm] -152.4)), FiO2 0.4 and PEEP 10 cmH2O during the whole study period. Respiratory rate will be titrated to keep end-tidal CO2 values between 30 and 40 mmHg. I:E ratio will be set in order to obtain an inspiratory time of 0.8 seconds and an inspiratory pause of 0.3 seconds and FiO2 will be kept unchanged during the whole study period. In patients in this group, recruiting maneuvers will be performed throughout a stepwise 5 cmH2O PEEP increase every 30 seconds to achieve a PEEP of 35 cmH2O during Pressure Controlled Ventilation (10 cmH2O of inspiratory pressure while keeping respiratory rate unmodified), followed by a stepwise 5 cmH2O PEEP reduction every 30 seconds until the baseline set peep is reached.

Arzneimittel: Intravenous anesthetic

Anaesthesia induction will be obtained with i.v. 2-3 mg/kg propofol, 0,6-0,8 mcg/kg fentanyl, and 0.9-1,2 mg/kg rocuronium. Anaesthesia will be maintained with i.v. propofol continuous infusion, with a dose titrated to achieve a bi-spectral index value between 40 and 50

Arzneimittel: Crystalloid Solutions

Balanced crystalloids will be administered to patients in both groups as a standard rate of 3-5 ml/kg/h. Treatment of eventual hemodynamic instability will be left to the attending physician

Diagnosetest: Esophageal pressure measurement

A nasogastric polyfunctional tube (Nutrivent, Sidam, Italy) will be placed after anaesthesia induction in all enrolled patients to measure esophageal pressure, estimate pleural pressure and compute transpulmonary pressure

Diagnosetest: Lung volume measurement with the nitrogen washin-washout technique

Lung volume will be measured through nitrogen wash-in wash-out technique and low-flow Pressure-volume curve will be recorded to estimate differences in alveolar recruitment between the two study groups.

Aktiver Komparator: Standard Ventilation

Volume controlled ventilation with tidal volume 10 ml/kg of PBW (45.5 + 0.91 (height [cm] -152.4)), FiO2 0.4 and PEEP 5 cmH2O during the whole study period. Respiratory rate will be titrated to keep end-tidal CO2 values between 30 mmHg and 40 mmHg. I:E ratio will be set in order to obtain an inspiratory time of 0.8-1 seconds and an inspiratory pause of 0.3 second

Arzneimittel: Intravenous anesthetic

Anaesthesia induction will be obtained with i.v. 2-3 mg/kg propofol, 0,6-0,8 mcg/kg fentanyl, and 0.9-1,2 mg/kg rocuronium. Anaesthesia will be maintained with i.v. propofol continuous infusion, with a dose titrated to achieve a bi-spectral index value between 40 and 50

Arzneimittel: Crystalloid Solutions

Balanced crystalloids will be administered to patients in both groups as a standard rate of 3-5 ml/kg/h. Treatment of eventual hemodynamic instability will be left to the attending physician

Diagnosetest: Esophageal pressure measurement

A nasogastric polyfunctional tube (Nutrivent, Sidam, Italy) will be placed after anaesthesia induction in all enrolled patients to measure esophageal pressure, estimate pleural pressure and compute transpulmonary pressure

Diagnosetest: Lung volume measurement with the nitrogen washin-washout technique

Lung volume will be measured through nitrogen wash-in wash-out technique and low-flow Pressure-volume curve will be recorded to estimate differences in alveolar recruitment between the two study groups.

Postoperative oxygenation

PaO2/FiO2 ratio 1 hour after extubation, while the patient is receiving oxygen through VenturiMask 40%

Postoperative forced expiratory volume in 1 second (FEV1)

volume exhaled during the first second of a forced expiratory maneuver started from the level of total lung capacity

Postoperative forced vital capacity (FVC)

the total amount of air exhaled during a forced expiratory maneuver started from the level of total lung capacity

Postoperative Tiffeneau index

computed as FEV1/FVC

Postoperative Dyspnea

Dyspnea assessed by Borg dyspnea scale

Pulmonary infection

modified clinical pulmonary infection score (mCPIS)

Postoperative pulmonary infiltrates

Evaluated with the chest x-ray by two independent clinicians blinded to treatment assignment

Intraoperative driving pressure

driving pressure, computed as Plateau pressure-PEEP

Intraoperative lung driving pressure

transpulmonary driving pressure, computed as Transpulmonary end-inspiratory pressure-transpulmonary total end-expiratory pressure

Intraoperative oxygenation

PaO2/FiO2

Intraoperative dead space

Approximated as the difference between End-tidal CO2 and PaCO2 divided by PaCO2

Lung recruitment

lung recruitment/changes in end expiratory lung volume between the two groups

Intraoperative blood pressure

Arterial blood pressure

Intraoperative respiratory system compliance

computed as Tidal volume/airway driving pressure

Intraoperative lung compliance

computed as Tidal volume/lung driving pressure