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: Ketamine should only be used in an environment such as the emergency department , where proper one - on - one monitoring is used and board - certified physicians skilled in airway management are directly involved in the care of the patient .
### Output Text:
<span class="chemical">Ketamine</span> should only be used in an environment such as the emergency department , where proper one - on - one monitoring is used and board - certified physicians skilled in airway management are directly involved in the care of the patient . 