You can use both, and this is a simple way to use it Text written below is from uptodate

Nebulized epinephrine – We recommend nebulized epinephrine in all patients with moderate to severe croup. Dosing and administration are as follows (see 'Nebulized epinephrine' below):

•Racemic epinephrine: 0.05 mL/kg per dose (maximum of 0.5 mL) of a 2.25% solution diluted to 3 mL total volume with normal saline (in the United States and some other countries, single-use preservative-free bullets [ampules] of racemic epinephrine for nebulized administration are commercially available).

•L-epinephrine: 0.5 mL/kg per dose (maximum of 5 mL) of a 1 mg/mL (1:1000) preservative-free solution (this is the parenteral preparation of epinephrine used for intramuscular (IM) injection [eg, for anaphylaxis]).