ALL001 A 4-year-old girl weighing 16 kg is brought to the emergency department by her preschool teacher 20 minutes after eating a snack containing tree nuts, presenting with acute-onset diffuse urticaria, marked lip and facial angioedema, audible inspiratory stridor, intercostal retractions, and sudden lethargy; on examination, her vital signs reveal a heart rate of 152 bpm, respiratory rate of 42 breaths/min, blood pressure of 78/46 mmHg, and an $SpO_2$ of 90% on room air.

a. What is the diagnosis? b. What is the diagnostic criteria? c. What is the first step of management? d. What is the drug used and dose? e. Even after administering the drug, the symptoms does not resolve, what is the next step? f. What is the differential diagnosis?