The effects of inverse ratio pressure- controlled ventilation on the gas exchange in patients undergoing robot assisted prostatectomy

INTERVENTION: Patients will be ventilated with tidal volume 7 ml/kg, inspiratory to expiratory ratio (I:E) of 1:2 in a pressure‐controlled mode (PCM)(initial ventilation). After abdominal insufflations of CO2, mechanical ventilation by pressure‐controlled mode (PCM) with 5 cmH2O PEEP and I:E of 2:1 will be applied to them during abdominal insufflation of carbon dioxide gas in Trendelenberg position (intervention). The inspiratory pressure will be set to deliver a tidal volume of 7 ml/kg during PCM. After desufflation of abdominal gas, the ventilation will returne to an initial ventilation method of PCM. CONDITION: prostate cancer robot‐assisted prostatectomy PRIMARY OUTCOME: airway pressures (peak and mean airway pressure and total PEEP) will be measured by continuous expiratory air sampling, using a mainstream sensor (CO2 SMO PLUS 8100, Novametrix Medical System Inc., Wallingford, CT) placed in‐line between endotracheal tube and the Y‐piece using S/5 monitor (Datex‐Engstrom, Helsinki, Finland). Arterial blood gas analysis. lung compliance will be monitored by continuous expiratory air sampling, using a mainstream sensor (CO2 SMO PLUS 8100, Novametrix Medical System Inc., Wallingford, CT) placed in‐line between endotracheal tube and the Y‐piece using S/5 monitor (Datex‐Engstrom, Helsinki, Finland). SECONDARY OUTCOME: heart rate through electrocardiogram radial arterial pressure (pulse wave analysis) INCLUSION CRITERIA: American Society of Anesthesiologists physical status 1,2 patients undergoing elective robot‐assisted prostatectomy