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: These patients had a second event of cardiac arrest , resulting in death , within 10 to 60 minutes .
### Output Text:
These patients had a second event of cardiac arrest , resulting in death , within 10 to 60 minutes . 