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: Regarding the effects of drug - induced hypotension on coronary blood flow , aortic and coronary sinus metabolic data ( pH , pO2 , pCO2 ) we could confirm that nitroprusside hypotension could be safely used to 30 % mean blood pressure decrease from control , trimetaphan hypotension to 20 % mean blood pressure decrease .
### Output Text:
Regarding the effects of drug - induced hypotension on coronary blood flow , aortic and coronary sinus metabolic data ( pH , pO2 , pCO2 ) we could confirm that <span class="chemical">nitroprusside</span> hypotension could be safely used to 30 % mean blood pressure decrease from control , <span class="chemical">trimetaphan</span> hypotension to 20 % mean blood pressure decrease . 