During Endoscopic Third Ventriculostomy Cushings reflex can be triggered by sudden increase in Intra Cranial Pressure (ICP) due to continuous ventricular irrigation. The solutions is to stop the irrigating fluid and check for egress of fluid to reduce the ICP.
Reference
van Aken J, Struys M, Verplancke T, de Baerdemaeker L, Caemaert J, Mortier E. Cardiovascular changes during endoscopic third ventriculostomy. Minim Invasive Neurosurg. 2003 Aug;46(4):198-201. doi: 10.1055/s-2003-42354. PMID: 14506561