**5.2 Shunt**

Shunting through these defects depends upon diameter of defect and balance between systemic and vascular resistance. Balance between systemic vascular resistance (SVR) and pulmonary vascular resistance (PVR) is essential in the anaesthetic management of patient with shunts.

Normal pulmonary: Systemic ratio (Qp:Qs ratio) is 1:1 which indicate either no shunting or bidirectional shunt of equal magnitude. Qp:Qs ratio of 2:1 indicate left to right shunt while less than 1:1 ratio (0.8:1) means right to left shunt. The ratio is estimated from oxygen saturation measurements at pulmonary veins, pulmonary artery, systemic arterial and mixed venous blood.
