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: In our patient , transient cardiac arrhythmia or respiratory dysfunction related to cocaine and / or ethanol use were the most likely causes of cerebral hypoperfusion .
### Output Text:
In our patient , transient cardiac arrhythmia or respiratory dysfunction related to <span class="chemical">cocaine</span> and / or <span class="chemical">ethanol</span> use were the most likely causes of cerebral hypoperfusion . 