**4. Investigation**

Polycythaemia is very common which increases blood viscosity and leads to thrombosis and infarction in cerebral, renal and pulmonary region. Although polycythaemia leads to intravascular volume expansion but at the same time reduces plasma volume. Coagulation abnormalities also occur due to hypofibrinogenaemia and factor deficiencies. Platelet count, PT and PTT should be ordered in all patients coming for surgery. Preoperative phlebotomy can be performed in patients with symptomatic hyperviscosity and haematicrit > 65%.

Electrolyte abnormalities are commonly seen in patients who receive diuretics and parental nutrition. Hypocalcaemia commonly found in patients with Di George syndrome.

ECG may show ventricular strain or hypertrophy pattern. Echocardiography is used for doppler and color flow mapping while catheterization is used for information about pressures in different chambers, magnitude of shunt and coronary anatomy. Examine chest X-Ray for heart position (Dextrocardia) and size, atelectasis, acute respiratory infection, vascular markings and elevated hemidiaphragm. High pulmonary flow will leads to increased pulmonary marking while reduced flow causes oligaemic lung fields.

Neurological assessment and MRI12 may also be needed in these patients. Delayed brain development is associated with certain CHD. Fetal MRI can help in early assessment of immature brain.
