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: The effects of continuous positive airway pressure ( CPAP ) on cardiovascular dynamics and pulmonary shunt ( QS / QT ) were investigated in 12 dogs before and during sodium nitroprusside infusion that decreased mean arterial blood pressure 40 - 50 per cent .
### Output Text:
The effects of continuous positive airway pressure ( CPAP ) on cardiovascular dynamics and pulmonary shunt ( QS / QT ) were investigated in 12 dogs before and during <span class="chemical">sodium nitroprusside</span> infusion that decreased mean arterial blood pressure 40 - 50 per cent . 