Accuracy of CO₂ monitoring via nasal cannulas and oral bite blocks during sedation for esophagogastroduodenoscopy

Esophagogastroduodenoscopy procedures are typically performed under conscious sedation. Drug-induced respiratory depression is a major cause of serious adverse effects during sedation. Capnographic monitoring of respiratory activity improves patient safety during procedural sedation. This bench study compares the performance of the nasal cannulas and oral bite blocks used to monitor exhaled CO₂ during sedation. We used a spontaneously breathing mechanical lung to evaluated four CO₂ sampling nasal cannulas and three CO₂ sampling bite blocks. We placed pneumatic resistors in the mouth of the manikin to simulate different levels of mouth opening. We compared CO₂ measurements taken from the sampling device to CO₂ measurements taken directly from the trachea. The end tidal CO₂ concentration (PetCO₂) measured through the bite blocks and nasal cannulas was always lower than the corresponding PetCO₂ measured at the trachea. The difference became larger as the amount of oxygen delivered through the devices increased. The difference was larger during normal ventilation than during hypoventilation. The difference became larger as the amount of oral breathing increased. The two nasal cannulas without oral cups failed to provide sufficient CO₂ for breath detection when the mouth was fully open and oxygen was delivered at 10 L/min. Our simulation found that respiratory rate can be accurately monitored during the procedure using a CO₂ sampling bite block or a nasal cannula with oral cup. The accuracy of PetCO₂ measurements depends on the device used, the amount of supplement oxygen, the amount of oral breathing and the patient’s minute ventilation.