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: However , there was no significant difference in the lidocaine concentrations measured when the systolic blood pressure became 70 mmHg .
### Output Text:
However , there was no significant difference in the <span class="chemical">lidocaine</span> concentrations measured when the systolic blood pressure became 70 mmHg . 