Surgeries requiring opening of chest cavity, might require, ventilation of only one lung, and other lung to be collapsed so that the surgery can be carried out easily. This is called one lung isolation/ventilation. This is also required in surgeries of one side lung. To achieve one lung ventilation, a specialised tube called Double lumen tube (DLT) is used. This tube is bigger in size as compared to a normal endotracheal tube used for ventilation during anaesthesia. Also, knowledge about exact size of the DLT is important as an undersized or oversized DLT can cause multiple problems. Oversized DLT can cause, trauma to the structures of windpipe, rupture of windpipe, not ventilating one lobe of the lung that needs to be ventilated and injury to teeth, tongue etc. An undersized DLT can cause dislodgement of tube after intubation, inadequate isolation of one lung, soiling of healthy lung etc.

                                   There are no standard formulas for calculating the size of DLT. Conventionally size of DLT is calculated based on patient demographics like height, weight and gender. However, studies have shown that this is not the right size for more than 50 percentage of cases. Preoperative CT scan provides measurements of trachea and bronchus which can be used to estimate size of appropriate DLT. This study aim to compare the two methods of selection of DLT.