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 haemodynamic effects of propofol in combination with ephedrine in elderly patients ( ASA groups 3 and 4 ) .
### Output Text:
The haemodynamic effects of <span class="chemical">propofol</span> in combination with <span class="chemical">ephedrine</span> in elderly patients ( ASA groups 3 and 4 ) . 