What Causes Rise In Pulse Level And Fever After Undergoing Brain Surgery?

A dear friend of mine has a 4 yr old grand daughter that just got out of a 12 hour brain surgery at St. Jude. they think they got the tumor.... this is her 3rd surgery in a year and a half, her pulse post op is spiking at 200 and she now has a fever of 102. do you think this is a side effect of the brain trauma ( high pulse) or aneurism?