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: A board - certified emergency physician skilled in airway management supervised administration of the anesthetic , and the patients were monitored by a registered nurse .
### Output Text:
A board - certified emergency physician skilled in airway management supervised administration of the anesthetic , and the patients were monitored by a registered nurse . 