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: Systemic aortic blood pressure and renal blood flow were measured continuously with a carotid arterial catheter and an electromagnetic flow probe respectively , in order to compare the cardiovascular and renal vascular effects of fenoldopam and sodium nitroprusside in ten dogs under halothane general anaesthesia .
### Output Text:
Systemic aortic blood pressure and renal blood flow were measured continuously with a carotid arterial catheter and an electromagnetic flow probe respectively , in order to compare the cardiovascular and renal vascular effects of <span class="chemical">fenoldopam</span> and <span class="chemical">sodium</span> <span class="chemical">nitroprusside</span> in ten dogs under <span class="chemical">halothane</span> general anaesthesia . 