A 3-day-old male neonate born to non-consanguineous parents presents with severe cyanosis and respiratory distress. On examination, he is deeply cyanotic with a single loud S2. Chest X-ray shows an 'egg-on-string' appearance with decreased pulmonary vascular markings. Echocardiography confirms complete transposition of the great arteries (TGA) with an intact ventricular septum. What is the immediate management priority in this neonate?