Evaluation of Regional Lung Mechanics in Obese Patients Undergoing Laparoscopic Surgery (OBESE-EIT)

Evaluation of Regional Lung Mechanics in Obese Patients Undergoing Laparoscopic Surgery Using Electrical Impedance Tomography

This study will evaluate what is the impact of laparoscopy and Trendelenburg position on lung regional ventilation distribution in obese patients, focusing on the differences between the different phases of surgery.

Electrical impedance tomography (EIT) is a non invasive monitoring technique that allows to evaluate the regional distribution of ventilation. EIT has been used in different contexts, such as acute respiratory failure or intraoperative ventilation settings. Obesity, by increasing intrabdominal pressure, may reduce functional residual capacity after anesthesia and therefore require a more aggressive intraoperative ventilatory setting. In addition, laparoscopy, by increasing the volume of the abdomen, further pushes the diaphragm and increase the probability of lung collapse. The aim of the current study is to describe the effect of 1) anesthesia and of 2) laparoscopy and trendelenburg position on regional ventilation distribution. Moreover, the investigators will evaluate if the best ventilatory parameters set after anesthesia induction are confirmed also when the condition changes (i.e. during pneumoperitoneum and trendellenburg). Finally, the investigators will explore if the different parameters which can be provided by EIT agree in suggesting the best level of positive-end expiratory pressure in both moments of surgery.

All patients will undergo a PEEP titration trial in each surgery step (before pneumoperitoneum, during pneumoperitoneum, after pneumoperitoneum). The PEEP titration trial will be done in steps of 2 cmH2O, starting from clinical PEEP 16 cmH2O and ending to PEEP 6 cmH2O. Each PEEP level will be kept for 2 minutes. The PEEP titration trial will be stopped in case of haemodynamic instability or severe desaturation (Spo2 < 92%). Each PEEP titration trial will be recorded using Electrical impedance tomography (EIT).

PEEP trial, starting from clinical PEEP 16 cmH2O and ending at PEEP 6 cmH2O. The PEEP trial will be stopped for haemodynamic instability (defined as arterial pressure < 80 mmHg and /or heart rate > 150 bpm) or desaturation (defined as SpO2 < 92%).

Secondary outcome will be to compare the different values of best PEEP provided by several parameters of EIT to evaluate if the overlap.

Inclusion Criteria: age 18-90 years Body mass index > 30 kg/m2 Major surgery Predicted duration of surgery > 2 hours Predicted presence of invasive arterial pressure monitoring Exclusion Criteria: emergency surgery Refuse to participate from patient presence of Implantable cardiac device or pacemaker thoracic wounds thoracic surgery

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