A 2-yeаr-оld bоy is brоught to а primаry care clinic with 2 days of congestion and a barking cough, but over the last several hours he has developed worsening noisy breathing and difficulty breathing. On examination, the child appears anxious and ill, is sitting upright in his mother’s lap, and has inspiratory stridor at rest, marked suprasternal and intercostal retractions, nasal flaring, and decreased oral intake. Oxygen saturation is 87% on room air. Which of the following is the most appropriate management?