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: Cauda equina syndrome after spinal anaesthesia with hyperbaric 5 % lignocaine : a review of six cases of cauda equina syndrome reported to the Swedish Pharmaceutical Insurance 1993 - 1997 .
### Output Text:
Cauda equina syndrome after spinal anaesthesia with hyperbaric 5 % <span class="chemical">lignocaine</span> : a review of six cases of cauda equina syndrome reported to the Swedish Pharmaceutical Insurance 1993 - 1997 . 