N2O increases CBF, CMR, and ICP. Mostly due to cerebral vasodilation, although partly due to sympathoadrenal stimulation. This effect is lessened by co-administration of IV anesthetics, but may be worsened by addition of volatile. CBF response to CO2 is preserved w/ N2O administration. According to Miller, “There is no uniform agreement about the effect of N2O on CMR… In a recent investigation in humans, administration of 70% N2O on a background of either sevoflurane or propofol anesthesia resulted in modest increases in CMRO2, thus indicating that N2O does indeed increase cerebral metabolism.
Kaike K Kaisti, Jaakko W Långsjö, Sargo Aalto, Vesa Oikonen, Hannu Sipilä, Mika Teräs, Susanna Hinkka, Liisa Metsähonkala, Harry Scheinin Effects of sevoflurane, propofol, and adjunct nitrous oxide on regional cerebral blood flow, oxygen consumption, and blood volume in humans. Anesthesiology: 2003, 99(3);603-13