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: RESULTS : Controlled hypotension was achieved within a shorter period using laryngeal mask using lower rates of remifentanil infusion and lower total dose of remifentanil .
### Output Text:
RESULTS : Controlled hypotension was achieved within a shorter period using laryngeal mask using lower rates of <span class="chemical">remifentanil</span> infusion and lower total dose of <span class="chemical">remifentanil</span> . 