In this study the Authors assume that peri-operative changes in DIA are predictive of postoperative atelectasis, thus providing a clinically useful tool to stratify the need for high-intensity monitoring, including admission to intensive care. Aim of this prospective observational study, in obese patients undergoing sleeve gastrectomy, is to evaluate the relationship between pre to postoperative changes in US-DIA and PaO2/FiO2.

Obese patients undergoing bariatric surgery, are at high risk for postoperative respiratory complications but predictive variables, risk factors and criteria for postoperative ICU admission are debated. In these patients, postoperative respiratory complications are related to various pathophysiological mechanisms that include: decreased lung volumes, respiratory muscle dysfunction and atelectasis. Very recently it has also been demonstrated a possible role of molecules that would mediate the fibro-adipogenic remodeling of the diaphragm in the obese, thus increasing the respiratory disability.

Pulmonary atelectasis appears within minutes after anesthesia induction, complicate 85-90% of the cases -involving up to 15% of the lungs and inducing a 5 to 10% of cardiac output intra pulmonary shunting- and determine an increased incidence of postoperative morbidity (with higher incidence of pneumonia). Furthermore, in the perioperative period, obese patients are more likely to develop atelectasis that resolves more slowly than in non-obese patients. Surgical handling of sub diaphragmatic region, as during sleeve gastrectomy, can impair diaphragmatic excursions thus contributing to postoperative pulmonary dysfunction. The same upper abdominal surgery represents a risk factor for the development of pulmonary complications in the perioperative period and alteration of the respiratory function indices.

Ultrasounds (US) imaging is a real-time, bedside, non-invasive technique that allows the quantitative evaluation of amplitude, force and velocity of diaphragmatic movement, including: diaphragmatic inspiratory amplitude (DIA) and diaphragmatic thickening. The US-DIA is a qualified quantitative approach to assess diaphragmatic function and has been reported to linearly correlate with vital capacity. Recent studies have also correlated diaphragmatic dysfunction, which reduces the ability to generate total current volume, with the onset of atelectasis, but in a very specialized and dedicated area such as thoracic surgery. The originality of the study lies in the fact that the investigators have translated this method of evaluation of diaphragmatic function, as a predictive index of pulmonary complications in postoperative surgery, into a highly selected and clinically demanding type of patient, such as the patient suffering from pathological obesity.

Several guidelines have been created at European level for the perioperative management of the obese patient. One of the most recent is the one created by the Italian Society of Anaesthesia Analgesia Rianimazione e Terapia Intensiva (SIAARTI), which commissioned an "Obesity Task Force" of the Airway Management Study Group to coordinate a multidisciplinary multi-professional consensus project to identify bundles of Good Clinical Practices (GCPs), useful to define the risks in adult obese patients in hospital.

In obese patients undergoing sleeve gastrectomy there are no conclusive criteria for discharge and indications to postoperative ICU admission, as recently defined for patients with OSAS, the investigators hypothesize that perioperative change in US-DIA predicts postoperative atelectasis, thus providing a clinically useful tool to stratify the need for higher intensity monitoring including ICU admission.

Inclusion Criteria:

• morbid obesity undergoing bariatric surgery (BMI >30 Kg/m2)

Exclusion Criteria:

• Heart Failure
• Neuromuscular Diseases
• Previous Thoracic Surgery,
• American Society of Anesthesiology physical (ASA) status >III.