Letters to the Editor
To the Editor:
Concerning the perspective article on capnography monitoring in procedural sedation for bronchoscopy. Several issues need to be considered.
With all due respect to the American Society of Anesthesiology guidelines and their goal to enhance safety during procedural sedation, flexible bronchoscopy differs greatly from gastrointestinal endoscopy and other procedural sedation. I would like to add a practical perspective that is specific to CO2 monitoring through a nasal cannula during flexible bronchoscopy. The CO2 monitoring nasal cannulas are designed to sample the CO2 from the right side prong and to deliver oxygen from the left side prong. If the bronchoscope is introduced through the right nostril, the nasal cannula will inevitably get displaced and the air flow through the right nostril will be completely or partially blocked by the bronchoscope causing the CO2 waveform to disappear or have a misleading abnormal shape. In contrast, if the bronchoscope is introduced through the left nostril, the flow of oxygen to the patient will be blocked causing an increase in the desaturation rate during bronchoscopy. In addition, suctioning of airway secretions during the procedure will further disrupt CO2 sampling making the interpretation of the waveform display difficult. During GI endoscopy such events are not generally noted because the endoscope is introduced through the mouth. Accordingly, the added cost of CO2 monitoring, the very low rates of sedation-related complications during flexible bronchoscopy, and impracticality of the CO2 sampling during flexible bronchoscopy should be considered before a change in practice is warranted.
Mona Sarkiss, MD, PhD
Departments of *Anesthesia and Periooperative Medicine
†Pulmonary Medicine, The University of Texas MD Anderson Cancer, Houston, TX