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: Mean ( IQR [ range ] ) length of stay in the intensive care unit was 115 ( 49 - 228 [ 32 - 481 ] ) h in patients with convulsive seizures compared with 26 ( 22 - 69 [ 14 - 1080 ] ) h in patients without seizures ( p < 0 . 001 ) .
### Output Text:
Mean ( IQR [ range ] ) length of stay in the intensive care unit was 115 ( 49 - 228 [ 32 - 481 ] ) h in patients with convulsive seizures compared with 26 ( 22 - 69 [ 14 - 1080 ] ) h in patients without seizures ( p < 0 . 001 ) . 