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: Twenty - four patients were anaesthetized for middle - ear surgery with deliberate hypotension induced by labetalol with isoflurane ( hypotensive group ) .
### Output Text:
Twenty - four patients were anaesthetized for middle - ear surgery with deliberate hypotension induced by <span class="chemical">labetalol</span> with <span class="chemical">isoflurane</span> ( hypotensive group ) . 