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 primary outcome of this study was a composite of severe hypotension ( mean arterial pressure < 60 mm Hg ) and bradycardia ( heart rate < 50 beats / min ) during sedative infusion .
### Output Text:
The primary outcome of this study was a composite of severe hypotension ( mean arterial pressure < 60 mm Hg ) and bradycardia ( heart rate < 50 beats / min ) during sedative infusion . 