The normal cerebral blood flow is guided by factors such as cerebral autoregulation (CA) and carbon dioxide reactivity (CO2R). Authors have demonstrated that CA and CO2R may be impaired in presence of intracranial tumors.Most studies pertaining to assessment of CA and CO2R in patients with brain tumors is limited to supratentorial tumors. Due to their anatomic location, posterior fossa tumors result in obstruction of ventricular outflow, produce hydrocephalus and features of raise intracranial pressure (ICP). It is possible that lesions in the posterior fossa may affect CA and CO2R. It should also be noted that posterior fossa surgeries are carried out in positions such as prone, lateral and sitting. Altered surgical positions themselves affect systemic hemodynamics which may influence cerebral blood flow; with presence of anesthetics further compromising the blood flow to the brain. Understanding the homeostatic mechanisms of CA and CO2R may help in deciding proper positioning of patients and maintenance of intraoperative hemodynamic.

The aim of this observational study was to evaluate CA and CO2R in patients with posterior fossa tumor prior to surgical decompression of the lesion.

Inclusion Criteria:

• All patients with posterior fossa tumor
• Scheduled for elective surgery
• History of recent ventriculoperitoneal shunt (within 24 hours)

Exclusion Criteria:

• previous craniotomy
• patients on ventilatory support
• history of cerebrovascular accident
• syncope or carotid artery disease
• anemia
• polycythemia
• patients on vasoactive medications
• those suffering from medical conditions such as diabetes mellitus and hypertension.

Due to their anatomic location, posterior fossa tumors result in obstruction of ventricular outflow, produce hydrocephalus and features of raise intracranial pressure (ICP). It is possible that lesions in the posterior fossa may affect Cerebral Autoregulation and Carbon dioxide reactivity. It should also be noted that posterior fossa surgeries are carried out in positions such as prone, lateral and sitting. Altered surgical positions themselves affect systemic hemodynamics which may influence cerebral blood flow; with presence of anesthetics further compromising the blood flow to the brain. Understanding the homeostatic mechanisms of CA and CO2R may help in deciding proper positioning of patients and maintenance of intraoperative hemodynamic.