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: In this report we describe the case of a 37 - year - old white woman with Ebstein ' s anomaly , who developed a rare syndrome called platypnea - orthodeoxia , characterized by massive right - to - left interatrial shunting with transient profound hypoxia and cyanosis .
### Output Text:
In this report we describe the case of a 37 - year - old white woman with Ebstein ' s anomaly , who developed a rare syndrome called platypnea - orthodeoxia , characterized by massive right - to - left interatrial shunting with transient profound hypoxia and cyanosis . 