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 : To review evidence - based treatment options in patients with cerebral edema complicating fulminant hepatic failure ( FHF ) and discuss the potential applications of hypothermia .
### Output Text:
BACKGROUND : To review evidence - based treatment options in patients with cerebral edema complicating fulminant hepatic failure ( FHF ) and discuss the potential applications of hypothermia . 