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 technique of continuous intravenous anaesthesia with ketamine was used successfully during the Somalia civil war in 1994 and in north Uganda in 1999 for 64 operations in 62 patients , aged from 6 weeks to 70 years , undergoing limb and abdominal surgery including caesarian sections and interventions in neonates .
### Output Text:
A technique of continuous intravenous anaesthesia with <span class="chemical">ketamine</span> was used successfully during the Somalia civil war in 1994 and in north Uganda in 1999 for 64 operations in 62 patients , aged from 6 weeks to 70 years , undergoing limb and abdominal surgery including caesarian sections and interventions in neonates . 