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: The mean arterial pressure was 77 + / - 2 mmHg ( 10 . 3 + / - 0 . 3 kPa ) before hypotension and 50 + / - 0 mmHg ( 6 . 7 + / - 0 . 0 kPa ) during hypotension in the hypotensive group , and 86 + / - 2 mmHg ( 11 . 5 + / - 0 . 3 kPa ) during anaesthesia in the control group .
### Output Text:
The mean arterial pressure was 77 + / - 2 mmHg ( 10 . 3 + / - 0 . 3 kPa ) before hypotension and 50 + / - 0 mmHg ( 6 . 7 + / - 0 . 0 kPa ) during hypotension in the hypotensive group , and 86 + / - 2 mmHg ( 11 . 5 + / - 0 . 3 kPa ) during anaesthesia in the control group . 