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 HEM - induced hypotension the cardiac output was significantly lower and systemic vascular resistance higher compared with that in the SNP group .
### Output Text:
During HEM - induced hypotension the cardiac output was significantly lower and systemic vascular resistance higher compared with that in the <span class="chemical">SNP</span> group . 