A 3-month-old previously healthy boy is brought to the emergency department in January with 2 days of cough, rhinorrhoea and increasing work of breathing. He has subcostal indrawing, diffuse crackles and wheezes, and oxygen saturation 92% on room air. He is feeding reasonably and has good urine output. According to the Canadian Paediatric Society bronchiolitis guideline, what is the most appropriate initial management?