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: Any pain during the reduction was rated by the orthopaedic surgeon treating the patient according to the Children ' s Hospital of Eastern Ontario Pain Scale ( CHEOPS ) .
### Output Text:
Any pain during the reduction was rated by the orthopaedic surgeon treating the patient according to the Children ' s Hospital of Eastern Ontario Pain Scale ( CHEOPS ) . 