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: RESULTS : Induction of anesthesia was followed by a decrease in MAP , HR , SV , and CO concomitant with an elevation in S ( c ) O ( 2 ) .
### Output Text:
RESULTS : Induction of anesthesia was followed by a decrease in MAP , HR , SV , and CO concomitant with an elevation in S ( c ) O ( 2 ) . 