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 myriad clinical presentation of myxedema coma and its serious morbidity and mortality stresses the need to suspect this clinical syndrome among CHF patients presenting with hypotension , weakness or other unexplained symptoms .
### Output Text:
The myriad clinical presentation of myxedema coma and its serious morbidity and mortality stresses the need to suspect this clinical syndrome among CHF patients presenting with hypotension , weakness or other unexplained symptoms . 