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: Furthermore , patients had no recall of words repeated prior to procedural sedation in BIS ranges associated with recall after procedural sedation , suggestive of retrograde amnesia .
### Output Text:
Furthermore , patients had no recall of words repeated prior to procedural sedation in BIS ranges associated with recall after procedural sedation , suggestive of retrograde amnesia . 