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: The severity of pain due to etomidate injection , mean arterial pressure , heart rate , and adverse effects were also evaluated .
### Output Text:
The severity of pain due to <span class="chemical">etomidate</span> injection , mean arterial pressure , heart rate , and adverse effects were also evaluated . 