In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: BACKGROUND : Dexmedetomidine has been used at our institution since 2005 to provide sedation for pediatric radiological imaging studies .
### Output Text:
BACKGROUND : <span class="chemical">Dexmedetomidine</span> has been used at our institution since 2005 to provide sedation for pediatric radiological imaging studies . 