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: Circumstances leading to this event and the mechanisms enabling a neuromuscular blockade to occur , following the administration of a small dose of relaxant , are discussed .
### Output Text:
Circumstances leading to this event and the mechanisms enabling a neuromuscular blockade to occur , following the administration of a small dose of relaxant , are discussed . 