Inhalational agents in today’s clinical practice alter the cerebral hemodynamics in a dose dependent fashion. Upwards of 1.0 MAC concentration cerebral vasodilatation is seen as intrinsic vasodilatory action of the volatile agents as well as decreased cerebral  resistance. The magnitude of cerebral vasodilatation is not uniform amongst the three widely used inhalational agents as shown by both human and animal studies. Cerebral vasodilatation is known to alter cerebral hemodynamics. Adequate brain relaxation is essential for neurosurgery to provide sufficient surgical exposure thereby minimising the risk of damage to the normal brain tissue. Presence of supratentorial tumors may impair cerebral autoregulation more so if the midline shift is more than 5 mm. As estimated by the neurosurgeons, subdural pressure monitoring after removal of bone flap correlates well with the dural tension. There are lack of methods by which cerebral blood flow (CBF) can be measured directly. There are lack of methods by which cerebral blood flow  can be measured directly. However, CBF can be indirectly measured by trans-cranial doppler (TCD) . When angle of insonation and vessel diameter remains constant, the middle cerebral artery (MCA) flow velocity provides an indirect measure of cerebral blood flow. Cerebral blood flow  changes due to volatile agents can be assessed by the MCA flow velocity as change in the MCA flow velocity is directly proportional to the change in CBF and TCD is a surrogate of CBF.

Pulsatility index (PI) is a non-invasive method of assessing vascular resistance in major blood vessels with the use of Doppler ultrasonography. PI more than 1.5 in Middle Cerebral artery using Transcranial Doppler has been shown to be an indicator of increased Intracranial Pressure.