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: We analyzed the following events : complications related with the topical anesthesia , with MZ use and with the procedure .
### Output Text:
We analyzed the following events : complications related with the topical anesthesia , with <span class="chemical">MZ</span> use and with the procedure . 