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: Serious adverse events occurred in seven women : six cases with blood loss > or = 1000 ml , four cases of manual placenta removal , five cases of additional oxytocics administration and five cases of blood transfusion .
### Output Text:
Serious adverse events occurred in seven women : six cases with blood loss > or = 1000 ml , four cases of manual placenta removal , five cases of additional oxytocics administration and five cases of blood transfusion . 