Et-C02 is used to predict PaCO2 during surgery. There are controversies regarding the value of ETCO2 to predict PaCO2. The aim of this study was to investigate the relation between Et-CO₂ and PaCO₂ measurements in patients undergoing laparoscopic colorectal surgery. Patient and surgical characteristics, mechanical ventilation adjustments, and intraabdominal pressure values and the corelation between these parameters and EtCO₂ - PaCO₂ difference were also investigated.