A 2-year-old child with croup has been intubated for 4 days…

A 2-year-old child with croup has been intubated for 4 days with a 4 mm ID uncuffed endotracheal tube. Heated aerosol at an FIO2 of 0.30 has been delivered to the patient. The physician asks the respiratory therapist to evaluate the patient for possible extubation. Which of the following would most likely indicate that the patient is ready for extubation?