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: Cerebral blood flow and metabolism during isoflurane - induced hypotension in patients subjected to surgery for cerebral aneurysms .
### Output Text:
Cerebral blood flow and metabolism during <span class="chemical">isoflurane</span> - induced hypotension in patients subjected to surgery for cerebral aneurysms . 