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: Monitoring consisted of airflow detection by a carbon dioxide analyser , chest wall movement detected by pneumatic capsules , and continuous electrocardiograph recorded with a Holter ambulatory monitor .
### Output Text:
Monitoring consisted of airflow detection by a <span class="chemical">carbon dioxide</span> analyser , chest wall movement detected by pneumatic capsules , and continuous electrocardiograph recorded with a Holter ambulatory monitor . 