Inclusion Criteria:  Age group: Adult patients from age of 21 years to 60 years Sex: Both sexes ASA Classification: patients with ASA classification II, III. Elective lung surgeries using video assisted thoracoscopic surgeries.  Exclusion Criteria:  Patients refuse to give informed consent. ASA Classification: ASA IV. Failure of thoracoscopic surgeries and continue as open thoracotomy Patients with ischemic heart diseases, where hypoxemia might be preexisting, or patient be more vulnerable to hypoxemia whatever the technique or time of hypoxia. Emergency lung surgeries. Patients underwent previous lung surgeries of any cause. Patients with pathology to the non-operated side.