Pulmonary complications are relatively frequent after surgery, and can be associated with an increase in morbidity and mortality. Although there are several causative mechanisms that can lead to postoperative pulmonary complications, alterations in the shape and motion of the chest wall are of primary importance.

In the investigator´s institution the incidence of postoperatory hypoxemia defined as pO2/FiO2 <300 is over 20% for patients after major abdominal surgery.

Observational and randomized clinical trials have demonstrated that incomplete neuromuscular recovery during the early postoperative period may result in acute respiratory events (hypoxemia and airway obstruction) and an increased risk of postoperative pulmonary complications.

A recent study in laparoscopic bariatric surgery showed that patients in which neuromuscular block reversal was done with sugammadex had less chest X-ray pathological changes than those from an historical cohort reversed with neostigmine.

The hypothesis is that differences in pulmonary complications, as atelectasis and hypoxemia, between patients reverted with sugammadex or neostigmine may be more apparent with more sensitive techniques like spirometry or lung ultrasound when they exist.

Lung ultrasound (LUS) has demonstrated a sensitivity of 90% and a specificity of 98%, to detect alveolar consolidation in critical ill patients while chest radiography data are known to be imprecise.The investigator would like to explore the utility of LUS in postsurgical patients and the relationship between degree of hypoxemia and consolidation area.

Objectives:

1. Primary: Forced vital capacity decreases after surgery. This reduction may be relieved in the absence of residual neuromuscular block. Objective is to assess differences after reversal with neostigmine versus sugammadex in:

   • Forced vital capacity (FVC)

2. Secondary objectives: To assess differences after reversal with neostigmine versus sugammadex in:

   • Atelectasis size determined by lung ultrasound (Plannimetry)
   • pO2/FiO2 <300 1 hour after surgery
   • Explore the accuracy of lung ultrasound (LUS) to diagnosis postoperative atelectasis and its correlation with chest Xray, FVC and pO2/FiO2.

Hypotheses:

1. Sugammadex NMB reversal results in a lower reduction of forced vital capacity (FVC) as compared to NMB reversal with neostigmine.
2. Atelectasis is common after major surgery. Size of atelectasis determined by lung ultrasound planimetry is lower one hour after sugammadex reversal as compared to the neostigmine group.
3. The incidence of post-surgical hypoxemia is lower in the sugammadex group as compared to the neostigmine group (Hypoxemia defined as pO2/FiO2 less than 300 is expected in 20% of patients after major abdominal surgery).
4. Lung ultrasound has a better capacity to detect alveolar consolidation than Chest Xray after major surgery.
5. Atelectasis size determine by planimetry has a good correlation with pO2/FiO2 and decrease of FVC after surgery

Inclusion Criteria:

• Every patient scheduled for major abdominal surgery (liver resection, pancreatectomy, gastrectomy or any type of colectomy) will be nominated to participate in the study.
• Informed consent will be asked for after their admission to the hospital the day before the surgery.
• Patients with postoperative epidural analgesia.

Exclusion Criteria:

• Refusal to participate.
• Entry to postoperative recovery unit under mechanical ventilation.
• Hypersensitivity reactions to any of the drugs.
• Severe asthma and mild asthma under treatment.
• Myocardial infarction or coronary occlusion three months prior to surgery.
• Myasthenia gravis.
• Emergency surgery.
• Pulmonary fibrosis or very severe chronic obstructive lung disease (GOLD IV)