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: Data were analyzed from all 747 consecutive patients who received dexmedetomidine for MRI sedation from April 2005 to April 2007 .
### Output Text:
Data were analyzed from all 747 consecutive patients who received <span class="chemical">dexmedetomidine</span> for MRI sedation from April 2005 to April 2007 . 