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 decreased from 86 + / - 5 ( s . e . mean ) mmHg to 52 + / - 1 mmHg ( 11 . 5 + / - 0 . 7 to 6 . 9 + / - 0 . 1 kPa ) for 98 + / - 10 min in the halothane ( H ) group , from 79 + / - 5 to 53 + / - 1 mmHg ( 10 . 5 + / - 0 . 7 to 7 . 1 + / - 0 . 1 kPa ) for 129 + / - 11 min in the enflurane ( E ) group , and from 80 + / - 4 to 49 + / - 1 mmHg ( 10 . 7 + / - 0 . 5 to 6 . 5 + / - 0 . 1 kPa ) for 135 + / - 15 min in the isoflurane ( I ) group .
### Output Text:
The mean arterial pressure was decreased from 86 + / - 5 ( s . e . mean ) mmHg to 52 + / - 1 mmHg ( 11 . 5 + / - 0 . 7 to 6 . 9 + / - 0 . 1 kPa ) for 98 + / - 10 min in the <span class="chemical">halothane</span> ( <span class="chemical">H</span> ) group , from 79 + / - 5 to 53 + / - 1 mmHg ( 10 . 5 + / - 0 . 7 to 7 . 1 + / - 0 . 1 kPa ) for 129 + / - 11 min in the <span class="chemical">enflurane</span> ( <span class="chemical">E</span> ) group , and from 80 + / - 4 to 49 + / - 1 mmHg ( 10 . 7 + / - 0 . 5 to 6 . 5 + / - 0 . 1 kPa ) for 135 + / - 15 min in the <span class="chemical">isoflurane</span> ( <span class="chemical">I</span> ) group . 