**5.2.1 Left to right shunt**


L –R shunt reduces greatly with drop in SVR or an increase in PVR. It leads to excess pulmonary blood flow. Patients are usually acynotic but deterioration in gas exchange may result from pulmonary congestion. Avoid 100% oxygen and hyperventilation in patients with L R shunt.

Patients with PDA are vulnerable to coronary ischaemia11 due to ongoing pulmonary runoff during the diastolic phase. Therefore diastolic blood pressure (DBP) should be monitored during surgery. Diameter of Modified Blalock Taussig shunt is fixed so its output is proportional to SVR and in case of systemic hypotension, the pulmonary blood flow will be reduced. Blood pressure in the arm will be low due to BT shunt, so use contralateral limb.
