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: During hypotension , the serum creatinine concentration rose significantly in all groups from the values before hypotension and returned postoperatively to the initial level in the other groups , except the isoflurane group .
### Output Text:
During hypotension , the serum <span class="chemical">creatinine</span> concentration rose significantly in all groups from the values before hypotension and returned postoperatively to the initial level in the other groups , except the <span class="chemical">isoflurane</span> group . 