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: These data indicate that nitroprusside infusion rates that decrease mean arterial blood pressure by 40 - 50 per cent do not change cardiac output or QS / QT .
### Output Text:
These data indicate that <span class="chemical">nitroprusside</span> infusion rates that decrease mean arterial blood pressure by 40 - 50 per cent do not change cardiac output or QS / QT . 