A 4-month-old boy presents to a community emergency department in January with 3 days of coryza, cough, and increasing work of breathing. He has subcostal indrawing, respiratory rate 60/min, oxygen saturation 93% on room air, and diffuse crackles and wheeze. He is feeding slightly less but has adequate urine output. According to the Canadian Paediatric Society bronchiolitis guideline, what is the most appropriate initial management?