The risk of bleeding is important during transsphenoidal surgery. This study aims to find if the ventilation mode, controlled pressure and controlled volume, modifies the risk of bleeding.

The risk of bleeding is important during transsphenoidal surgery. This study aims to find if the ventilation mode, controlled pressure and controlled volume, modifies the risk of bleeding.

• group Volume controlled ventilation: tidal volume of 7 mL/kg ideal body weight, frequency of 12 cycles/minute, I/E ratio of 1:2, no positive end expiratory pressure. Ventilatory frequency is changed if necessary to maintain end-expiratory pressure of CO2 between 35 and 40 mmHg.
• group Pressure-controlled ventilation: initial pressure of 15 cm H2O, frequency of 12 cycles/minute, I/E ratio of 1:2, no positive end expiratory pressure. Pressure is modified to maintain a tidal volume of 7 mL/kg of ideal body weight and frequency ventilation is modified to maintain end-expiratory pressure of CO2 between 35 and 40 mmHg.
• In both groups, the fraction of inspired oxygen is 50%. A recruitment maneuver is performed if the blood oxygen saturation became less than 92%.

Inclusion Criteria:

• Aged > 18 years
• Patients scheduled for transsphenoidal surgery for pituitary adenomas

Exclusion Criteria:

• Pregnancy
• Obesity (BMI> 35)
• Known respiratory disease
• Redo surgery
• Preoperative problem with hemostasis (antiplatelet or anticoagulant treatment; constitutional disorder).