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: A transient neurological deficit following intrathecal injection of 1 % hyperbaric bupivacaine for unilateral spinal anaesthesia .
### Output Text:
A transient neurological deficit following intrathecal injection of 1 % hyperbaric <span class="chemical">bupivacaine</span> for unilateral spinal anaesthesia . 