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: Resuscitation was considered successful when a systolic arterial pressure > or = 100 mm Hg was achieved within 5 min .
### Output Text:
Resuscitation was considered successful when a systolic arterial pressure > or = 100 mm Hg was achieved within 5 min . 