After Institutional Review Board approval from Ege University (Ethical Committee No. 16-10/13, 09.12.2016) and written informed consent, 200 patients aged 18-75 years, ASA physical status I-II, who were planned for elective urological surgery in one of the supine, prone, lateral flank or lithotomy position were studied. The exclusion criteria were as follows: emergency operation, a history of chronic lung disease, upper and/or lower respiratory tract infection within 2 weeks before surgery, morbid obesity, pregnancy, laparoscopic surgery, single lung ventilation, difficut airway, hemodynamic instability and/or respiratory complications in the intraoperative period, history of mental illness or communication problems.

The patients were divided into four groups according to the operation position as supine, lateral flank, prone and lithotomy. After the patient was taken to the operating room, routine vital sign monitoring of non-invasive arterial blood pressure (NIBP), electrocardiogram (ECG) and pulse oximetry (SpO2) was performed. Oxygen mask was connected and 3 minutes %100 preoxygenation was applied. Intravenous (IV) vascular access was provided and fluid therapy was started. For induction of general anesthesia, 10 mcg/kg atropine, 1mg/kg lidocaine, 2-3 mg/kg propofol, 1-3 µg/kg fentanyl and 0,6 mg/kg rocuronium bromide were administered intravenously.

After adequate mask ventilation, female patients were intubated orotracheally with a tube of internal diameter (ID) 7-7.5mm, while male patients were intubated with a tube of ID 8-8.5mm. The equal ventilation of both lungs was confirmed by oscultation, and the position of the endotracheal tube was determined after observing the waveform of ETCO2 on the capnograph. High volume, low pressure endotracheal tubes were used for intubation. Patients who were to undergo surgery in the prone position were also intubated with a spiral tube of the same number. After intubation, the cuff of the ETT was inflated with air through an injector of 5-10 mL as a standard method, and the pressure value of the cuff after intubation (T0) was measured and recorded in a neutral head position using an analog cuff manometer (VBM Medizintechnik®, GmbH, Germany). Immediately after that, the cuff pressure was adjusted to 25 cmH2O. The manometer continuously monitored the cuff pressure without separating it from the pilot balloon of the ETT. The patient was taken volume-controlled mechanical ventilation support with a tidal volume of 6-8 mL/kg, respiratory rate of 12-16/min, and ETCO2 of 35-40 mmHg. For anesthesia maintenance, a mixture of 50% O2 and air was used, along with Sevoflurane (Sevorane Liquid 250 ml®, Abbott, UK) at 2% MAC and remifentanil infusion.

Before and after giving the patient the necessary position for the operation, the cuff pressure was measured and recorded at T1 and T2, respectively. After giving the position, attention was paid to keeping the head in a neutral position relative to the body. To prevent the effect of airway pressure on the manometer during cuff pressure measurement, the value seen at the end of expiration was recorded. Subsequently, values at 5 minutes (T3), 10 minutes (T4), 15 minutes (T5), 30 minutes, 45 minutes, 60 minutes, 90 minutes, 120 minutes, 150 minutes, and 180 minutes were recorded during the operation. In addition, during the operation, parameters such as blood pressure, heart rate, SpO2, end-tidal CO2 (ETCO2), tidal volume, respiratory rate, mean airway pressure (MAP), and peak airway pressure (PAP) were monitored and recorded. There was no intervention in cuff pressure values during the monitoring period. Finally, after the surgical procedure was completed (T6) and before extubation after patients were put in a neutral (supine) position for waking up, cuff pressure and other parameter values were recorded. Patients were interviewed to determine if they had any complaints of sore throat, hoarseness, or cough at postoperative 2nd and 12th hours.

According to a previous study (10) the mean (SD) ETT cuff pressure was increased by 6.5 (3.9) cm H2O after the positional change from the supine to the lateral decubitus position. Assuming that the difference in the mean cuff pressure is reduced by 50% (3.25 cm H2O), we calculated that 23 patients would be needed in each group with a = 0.05 and b = 0.20. In our study, 50 patients per group were included.

The data were analyzed using the SPSS for Windows 21.0 software. Demographic data were calculated as mean standart deviation (min-max). Differences between data were analyzed using the t-test. For comparing repeated measurements, One-Way Analysis of Variance (One-Way ANOVA) was used. Post Hoc tests were used for between group comparisons. A p-value less than 0.05 was considered statistically significant.