Abstract We hypothesize that capnography could detect hypoventilation during induction of bronchoscopic sedation and starting bronchoscopy following hypoventilation, may decrease hypoxemia. Patients were randomized to: starting bronchoscopy when hypoventilation (hypopnea, two successive breaths of at least 50% reduction of the peak wave compared to baseline or apnea, no wave for 10 seconds) (Study group, n = 55), or when the Observer Assessment of Alertness and Sedation scale (OAAS) was less than 4 (Control group, n = 59). Propofol infusion was titrated to maintain stable vital signs and sedative levels. The hypoventilation during induction in the control group and the sedative outcome were recorded. The patient characteristics and procedures performed were similar. Hypoventilation was observed in 74.6% of the patients before achieving OAAS