Comparison of cerebral vasodilatory effects of sevoflurane, isoflurane & desflurane in patients undergoing surgery for supratentorial lesions under general anesthesia

Volatile anesthetics have a dual effect on cerebral vasculature. In low concentrations, they constrict cerebral vessels secondary to suppression of metabolism. With increasing concentration, the direct vasodilatory effect of volatile anesthetics turns dominant, leading to increased cerebral blood flow and brain volume. An increase in Cerebral blood volume will result in an increase in brain bulk in absence of autoregulation and eventually makes surgical access difficult.

Transcranial Doppler (TCD) provides an indirect measure of CBF by measuring blood flow velocity in Middle Cerebral artery, if the angle of insonation and vessel diameter remain constant. Although Middle Cerebral artery (MCA) flow velocity does not reflect absolute Cerebral Blood flow (CBF), change in MCA flow velocity is directly proportional to change in CBF.

Pulsatility index (PI) is defined as the difference between the peak systolic flow and minimum diastolic flow velocity, divided by the mean velocity recorded throughout the cardiac cycle. It is a non-invasive method of assessing vascular resistance in major blood vessels with the use of Doppler ultrasonography. PI >1.5 in Middle Cerebral artery using Transcranial Doppler has been shown to be an indicator of increased Intracranial Pressure.

NIRS is a non-invasive monitor, well suited for repeated measurement of cerebral oxygen saturation changes. It has been used to monitor cerebral autoregulation, based on the assumption that the brain’s oxygen content is positively related to cerebral blood flow.

Isoflurane is a widely used volatile anesthetic in neurosurgical procedures and has been shown to cause cerebral vasodilatation, especially at concentrations required to induce deep plane of anesthesia.

Sevoflurane, a newer volatile anesthetic agent, is very similar to isoflurane in its cardiovascular effects. Although sevoflurane has been shown to have similar cerebral vascular effects to isoflurane in animals, this has not been a consistent finding in humans.

Desflurane, a more recently introduced volatile anesthetic agent, has been shown to induce more cerebral vasodilatation than sevoflurane and isoflurane in animals. In humans, cerebral vascular properties of desflurane are similar to that of isoflurane.

Cerebral autoregulation has been observed to be impaired in patients with large supratentorial lesion and midline shift more than 5 mm.

There has been paucity of literature on comparison of cerebral vasodilatory properties of isoflurane, sevoflurane and desflurane. There is also sparse literature on the cerebrovascular effects of volatile anesthetic agents in supratentorial lesions. To fill this knowledge gap, we propose a comparative study of cerebral vasodilatory effects of isoflurane, sevoflurane, and desflurane.

We hypothesize that Cerebral Vasodilatory Effects of Sevoflurane, Isoflurane and Desflurane are comparable in patients undergoing surgery for supratentorial lesions under surgical depth of anesthesia.