Patients undergoing thyroidectomy will be divided into three groups (30 cm H2O Group I, 40 cm H2O Group II, 50 cmH2O Group III). At the end of the operation patients will be applied peak airway pressure manually according to involved groups.The time until the first hemorrhage is seen in each group or if not seen pressure will be applied for 30 seconds and then will be ended.We will record the blood pressure, spO2, HR, the first ETCO2 after the procedure, postoperative haemorrhage that required surgery, and postoperative hematomas during peak airway pressure increase during the operation in all patients. The 1st hour blood pressure, nausea-vomiting score and pain score (NRS) will be recorded in the postoperative recovery unit.

The primary end point of the study is intraoperative bleeding detected, and the secondary end point is postoperative bleeding.

Patients will be divided into three groups (https://www.randomizer.org/) by computer assisted randomization method (30 cm H2O in Group I, 40 cm H2O in Group II, 50 cmH2O in Group III peak pressure will be applied). The time until the first hemorrhage is seen in each group or if not seen pressure will be applied for 30 seconds and then will be ended.

Patients will be taken to the operation table and standard monitorization will be performed consisting of ECG, non-invasive blood pressure and peripheral O2 saturation from the back region. Anesthesia was induced with 2 mg / kg propofol (propofol 1% Fresenius, Fresenius Kabi, Germany), 2 mg / kg fentanyl (Talinat 0,5mg / 10ml, AND, Turkey), 0.6 mg / kg rocuronium (Muscuro 50mg / 5ml, Kocak Farma , Turkey) will be provided after the patients were intubated orally. General anesthesia treatment will be provided with 2% Sevoflurane in 40% oxygen-air mixture. All patients will be ventilated in pressure controlled mode; respiratory frequency: 12 / min, FiO2: 40% (oxygen-air mixture), I/E:1/2, PEEP: 7 cmH2O supplying end tidal CO2 value of 32-36 mmHg.

Calculating the ideal weight of the patient, isolated-S (Polifarma, Turkey)2ml/kg/h will be infused. If the systolic arterial pressure (SAB) or heart rate (HR) increases by 20% compared to baseline, IV 50 μg fentanyl will be administered. At the end of the operation, the patient's airway peak pressure will be increased before hemostasis is provided by the same surgeon (S.T.). Positive pressure on the Maquet Flow I device (Maquet Flow I-AGC, Rastatt, USA) will be applied manually(30 cm H2O in Group I, 40 cm H2O in Group II patients and 50 cm H2O in group III patients). The airway peak pressure increase will be maintained and recorded until the surgeon sees the first bleeding point or if not seen for 30 seconds. For all three groups this process will be repeated one more time.

After peak airway pressure is increased, the number of bleeding centers detected, how long time did it take to detect and the size of the bleeding vessel (<2 mm or> 2 mm)will be recorded. We will record the blood pressure, spO2, HR, the first ETCO2 after the procedure, postoperative haemorrhage that required surgery, and postoperative hematomas during peak airway pressure increase during the operation in all patients. The 1st hour blood pressure, nausea-vomiting score and pain score (NRS) will be recorded in the postoperative recovery unit.

The primary end point of the study is intraoperative bleeding detected, and w the secondary end point is postoperative bleeding.

Inclusion Criteria:

• ASA classification I-II patients
• Patients undergoing total thyroidectomy
• Aged between 18-60 years

Exclusion Criteria:

• Active pulmonary disease
• Cardiac aritmia
• Intracranial mass
• Coagulation defects