Procedure sedation of flexible bronchoscopy (FB) comforts patients undergoing FB. Hypoventilation during FB is a concern. The investigators investigate the feasibility of monitoring capnography in FB sedation.

Patients undergoing flexible bronchoscopy (FB) experience procedure-related symptoms. Current guidelines of FB recommend sedation to all patients undergoing FB, except when there are contraindications. Propofol or benzodiazepines plus an opioid are the common combination used to improve patient tolerance and satisfaction during FB. However, controversy about combining propofol and opioids persists because of the risk of over-sedation and cardiopulmonary depression.

While transition from alert into sedation during induction, like sleep, the respiratory drive and muscle tone of respiratory muscle and upper airway attenuate, which contribute hypoventilation and upper airway collapse, and further hypoxemia. Detection of cardiopulmonary depression traditionally has relied on continuous monitoring of heart rate, respiratory rate, and oxygen saturation. However, it has been shown that these monitors could not recognize hypoventilation early. Similar with other published data, around 40% of hypoxemia event occurred during FB sedation in our hospital. Further analysis of our data revealed around 15% event occurred during sedative induction.

Capnography is the noninvasive measurement of the partial pressure of carbon dioxide (CO2) from the airway during ventilation. The maximum partial pressure of CO2 obtained at the end of an exhaled breath is referred to as end-tidal CO2 (EtCO2). Studies have revealed the waveform analysis of capnography can provide early warning for prehypoxic respiratory depression in patients undergoing procedure sedation in emergency department and gastrointestinal endoscopy. Therefore, capnography can serve as a real-time measure of ventilatory status of sedative patients and the physicians could intervene before the occurrence of hypoxemia. Based on the advantage of non-invasive and real-time property of EtCO2 monitored by capnography, the investigators plan to conduct a clinical trial to evaluate if hypoxemia could be reduced by capnography of EtCO2 monitor during induction of FB sedation.

Inclusion Criteria:

• Patients undergoing elective bronchoscopy and sedation

Exclusion Criteria:

• Age less than 18 years
• American Society of Anaesthesiologists (ASA) physical status classification IV or V
• Mallampati score of 4
• Severe sleep apnoea syndrome (apnoea-hypopnea index more than 40)
• Body mass index more than 42 in males or 35 in females
• Neurologic disorders or other conditions contributing to difficulty in assessing response
• Forced expiratory vital capacity (FVC) less than 15 ml/kg body weight, forced expiratory volume in one second (FEV1) less than 1000 ml, or FEV1/FVC less than 35%
• Chronic use of opioid drugs
• Pregnancy
• Patients with a known history of allergy to the study drugs, or to eggs, soybeans or sulfite products