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: Because DTIs do not have reversal agents , surgical teams and transfusion services should remain aware of the possibility of massive transfusion events during anticoagulation with these agents .
### Output Text:
Because DTIs do not have reversal agents , surgical teams and transfusion services should remain aware of the possibility of massive transfusion events during anticoagulation with these agents . 