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 purpose of this review was to perform a retrospective analysis to examine whether there was a relation between TXA usage and seizures after cardiac surgery .
### Output Text:
The purpose of this review was to perform a retrospective analysis to examine whether there was a relation between <span class="chemical">TXA</span> usage and seizures after cardiac surgery . 