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 results suggest that PGE1 may be preferable to TMP for hypotensive anaesthesia in spinal surgery because TMP decreased EBF .
### Output Text:
These results suggest that <span class="chemical">PGE1</span> may be preferable to <span class="chemical">TMP</span> for hypotensive anaesthesia in spinal surgery because <span class="chemical">TMP</span> decreased EBF . 