In past studies comparing L-DLT to BB, time to get CLC was measured from the beginning of OLV. Nevertheless, the interval between this time point and the pleural opening (PO) is sometime difficult to control. Technical incidents can prolong this period and induce a bias. Furthermore, in the last investigator's protocol, the second period of apnea is done at pleural opening. For these reasons, the authors consider that the time to get CLC should be measured from the pleural opening since it is the crucial moment for the surgical team. Investigators are proposing to evaluate the PO-CLC interval as a primary objective.(6)