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: Subsequent addition of phenylephrine infusion , sufficient to re - elevate mean arterial pressure to 106 + / - 4 mm Hg ( P less than 0 . 001 ) for 30 minutes , increased left ventricular filling pressure to 17 + / - 2 mm Hg ( P less than 0 . 05 ) and also significantly increased sigmaST ( P less than 0 . 05 ) .
### Output Text:
Subsequent addition of <span class="chemical">phenylephrine</span> infusion , sufficient to re - elevate mean arterial pressure to 106 + / - 4 mm Hg ( P less than 0 . 001 ) for 30 minutes , increased left ventricular filling pressure to 17 + / - 2 mm Hg ( P less than 0 . 05 ) and also significantly increased sigmaST ( P less than 0 . 05 ) . 