Persistent Hypoxemia in an Asymptomatic 4-year-old Boy

A 4-year-old boy with a history of anaphylaxis to peanuts and tree nuts presents to a local emergency department (ED) with an acute allergic reaction and a peripheral oxygen saturation by pulse oximetry (Spo₂) of 85% on room air. Before coming to the ED, he was in his usual state of health and playful. After eating a peanut, he developed acute facial swelling and pruritus, with no coughing or trouble breathing. In the ED he is afebrile with no signs of dyspnea, cyanosis, or respiratory distress. His pruritus and facial swelling improve after receiving intramuscular epinephrine and oral corticosteroids, which were given for potential anaphylaxis. Because he remains hypoxemic without respiratory complaints, he is transferred to our facility for further evaluation, where his heart rate and blood pressure are within normal limits for his age and his lungs are clear to auscultation bilaterally without wheezing. He has...