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 : The purpose of this study was to compare surgical conditions , including the amount of intraoperative bleeding as well as intraoperative blood pressure , during functional endoscopic sinus surgery ( FESS ) using flexible reinforced laryngeal mask airway ( FRLMA ) versus endotracheal tube ( ETT ) in maintaining controlled hypotension anesthesia induced by propofol - remifentanil total i . v . anesthesia ( TIVA ) .
### Output Text:
BACKGROUND : The purpose of this study was to compare surgical conditions , including the amount of intraoperative bleeding as well as intraoperative blood pressure , during functional endoscopic sinus surgery ( FESS ) using flexible reinforced laryngeal mask airway ( FRLMA ) versus endotracheal tube ( ETT ) in maintaining controlled hypotension anesthesia induced by <span class="chemical">propofol</span> - <span class="chemical">remifentanil</span> total i . v . anesthesia ( TIVA ) . 