Anesthetic Management of Patients with Supratentorial Tumours

a) Pneumocephalus:The sitting position increases the likelihood of significant pneumocephalus. In this position, air readily enters the subarachnoid space as CSF is lost during surgery.Postoperative pneumocephalus can cause delayed awakening and continued impairment of neurological function.b) Venous air embolism:Venous air embolism can occur when the pressure within an open vein is subatmospheric. The incidence of venous air embolism is highest during sitting craniotomies (20-40%).The physiological consequences of venous air embolism depend on the volume, the rate of air entry.When the amount entrained exceeds the rate of pulmonary clearance, pulmonary artery pressure progressively rises.Clinically, signs of venous air embolism are often not apparent until large amounts of air have been entrained. Rapid entrainment of large amounts of air can produce sudden circulatory arrest by obstructing right ventricular outflow when intracardiac air impairs tricuspid and pulmonary valve function or blocks pulmonary arterioles..