Subjects were enrolled at the University of Oklahoma Health Sciences Center from June 2009 to December 2009. Study inclusion criteria included subjects 18 to 99 years of age with the presence of an endobronchial mass seen on chest imaging and the need for flexible bronchoscopy with endobronchial biopsies. An arterial blood gas was obtained preprocedurally on all patients. Exclusion criteria included a Paco2 > 47 mm Hg, long-term oxygen therapy, unwillingness to undergo flexible bronchoscopy, coagulopathy (defined as a platelet count < 100,000/μL, an international normalized ratio > 1.4, or a known clinical bleeding disorder), or current therapy with an anticoagulant (including warfarin and clopidogrel). Additional exclusion criteria included renal dysfunction (defined as a creatinine > 2 mg/dL), life-threatening arrhythmias, history of myocardial infarction or cerebrovascular accident within the preceding 6 months, facial abnormalities preventing safe introduction of the bronchoscope, uncontrolled hypertension, active liver disease, pregnancy, breastfeeding, or inability to give informed consent. The study was approved by the institutional review board at the University of Oklahoma Health Sciences Center, and informed consent was obtained for all subjects.