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: Several risk factors for NMS should be noted in elderly depressive patients whose symptoms often include dehydration , agitation , malnutrition , and exhaustion .
### Output Text:
Several risk factors for NMS should be noted in elderly depressive patients whose symptoms often include dehydration , agitation , malnutrition , and exhaustion . 