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: We included prospective , randomised peri - operative studies of dexmedetomidine that reported mortality , cardiac morbidity or adverse drug events .
### Output Text:
We included prospective , randomised peri - operative studies of <span class="chemical">dexmedetomidine</span> that reported mortality , cardiac morbidity or adverse drug events . 