Perioperative fluid management is a key component of anesthetic management during thoracic surgery. On one hand, fluid restriction could compromise perfusion of vital organs and surgical anastomosis. On the other hand, fluid overload could lead to cardiopulmonary complications, notably pulmonary edema, which carries a high mortality rate. Perioperative fluid management to avoid postpneumonectomy pulmonary edema has been previously reviewed. Therefore, to achieve the balance between preventing fluid overload and optimising organ perfusion, the practical index to guide fluid management, which can predict whether fluid loading will improve haemodynamic conditions in an individual patient, would be very valuable during lung surgery. Perioperative goal-directed fluid therapy (GDFT) is a cornerstone of tissue perfusion and oxygenation, and it can improve surgical outcomes. Respiratory variations of arterial pressure [i.e. pulse pressure variation (PPV) and systolic pressure variation] can predict fluid responsiveness in mechanically ventilated patients under various conditions. Therefore, pressure variations are increasingly being advocated for fluid management.This study will discuss the effects of pulse pressure variation(PPV) in different level during anesthesia on patients with oxygenation index and short-term prognosis undergoing video-assisted thoracoscopic surgery for pneumoresection.

Inclusion Criteria:

• American Society of Anesthesiologists physical status I-III; aged 18-60 years old; BMI 18.5 ~ 28 kg/m2

Exclusion Criteria:

• Refused to participate in the experiment, hepatic/renal/cardiac dysfunction, severe valvular disease, frequent arrhythmia, moderate anemia and severe electrolyte disturbance before operation.