A 58-year-old woman with a history of epiglottitis (currently treated with antibiotics and dexamethasone) is scheduled for urgent airway assessment. She has stridor, dysphagia, and drooling but maintains her airway. Oxygen saturation is 94% on room air. The otolaryngologist and anesthesiologist decide that awake fiberoptic intubation is the safest approach. During the procedure, after successful topical anesthesia and light sedation with remifentanil, the fiberoptic scope is advanced through the nose. As the scope reaches the epiglottis, the patient suddenly coughs vigorously and desaturates to 88%. What is the MOST appropriate immediate action?