In cases of severe croup, racemic epinephrine acts primarily to:

In cases of severe croup, racemic epinephrine primarily acts to reduce airway edema. It is a nebulized medication that contains both enantiomers of epinephrine, which have potent vasoconstrictive properties. When administered, it constricts blood vessels in the airway mucosa, leading to a decrease in swelling and edema, which can significantly alleviate the stridor and respiratory distress associated with croup.

The action of racemic epinephrine helps to temporarily relieve symptoms by reducing inflammation and allowing for easier airflow through the upper airway. While it may have some effects on lung function by improving airway patency, its primary and immediate benefit in the context of croup is the reduction of edema. Sedation is not a primary action of this medication, and it does not have the role of increasing pulmonary blood flow. Thus, the primary focus of using racemic epinephrine in severe croup scenarios is its effectiveness in reducing airway swelling.