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: Systolic pressure variation is greater during hemorrhage than during sodium nitroprusside - induced hypotension in ventilated dogs .
### Output Text:
Systolic pressure variation is greater during hemorrhage than during <span class="chemical">sodium nitroprusside</span> - induced hypotension in ventilated dogs . 