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: Increasing doses of catecholamines , sedatives , and muscle relaxants administered through a central venous catheter were ineffective .
### Output Text:
Increasing doses of <span class="chemical">catecholamines</span> , sedatives , and muscle relaxants administered through a central venous catheter were ineffective . 