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: AIM : To determine the hemodynamic responses , efficacy and adverse events associated with the use of high dose dexmedetomidine as the sole sedative for magnetic resonance imaging ( MRI ) studies .
### Output Text:
AIM : To determine the hemodynamic responses , efficacy and adverse events associated with the use of high dose <span class="chemical">dexmedetomidine</span> as the sole sedative for magnetic resonance imaging ( MRI ) studies . 