The investigators hypothesize that large doses of fluids used during intraoperative could affect lung parenchyma structure and, consequently, gas exchange and respiratory mechanics. The purpose of this study is to evaluate fluids effects on oxygenation, respiratory mechanics, by using two different solutions: crystalloid or colloid.

Inclusion Criteria:

• patients undergoing elective abdominal, thoracic, vascular surgery
• minimum age 18 years
• informed consent

Exclusion Criteria:

• patients with severe cardiomyopathy or severe heart failure
• history of coagulation disorders
• patients with severe cardiovascular or respiratory disorders
• renal insufficiency

Respiratory mechanic parameters (i.e., inspiratory peak pressure, plateau pressure, total airway resistance, and static compliance) are obtained .Blood samples are drawn simultaneously from the arterial catheters for gas analysis. Data were collected after induction of anesthesia (T0) after 1 h (T1), 2 h (T2), 3 h (T3) and at the end of surgery.

Primary outcome: evaluate the fluids effects on oxygenation, respiratory mechanics

Secondary outcome: Incidence of surgery related complications

Inclusion Criteria:

• patients undergoing elective abdominal, thoracic, vascular surgery
• minimum age 18 years
• informed consent

Exclusion Criteria:

• patients with severe cardiomyopathy or severe heart failure
• history of coagulation disorders
• patients with severe cardiovascular or respiratory disorders
• renal insufficiency
• severe liver diseases