An 18-month-old boy has tetralogy of Fallot. His symptoms include irritability, cyanosis and tachypnoea. He has suffered one episode of syncope. Which of the following manoeuvres is the best treatment for these episodes?

d. Tetralogy of Fallot is the most common congenital cyanotic heart abnormality. This abnormality is characterised by variable obstruction to the right ventricular outflow due to pulmonary stenosis, dextroposition of the aorta overriding the ventricular septum, ventricular septal defect (VSD) and right ventricular hypertrophy. Due to the VSD there is a shunt of blood from the left to the right side of the heart. Children have learned that squatting decreases the cyanosis and the hypoxaemia. This increases the left ventricular afterload and decreases the left to right shunt. Other mechanisms listed in the question do not have any effect on the left to right shunting of the blood flow in the heart.