In transposition of the great arteries, which intervention helps maintain systemic mixing before corrective surgery?

• A. Keep the patent ductus arteriosus (PDA) and patent foramen ovale (PFO) open
• B. Close the PDA immediately
• C. Rely only on pulmonary circulation with no mixing
• D. Proceed to arterial switch without prostaglandins

Answer: (A)

In transposition of the great arteries, the aorta comes off the right ventricle and the pulmonary artery off the left ventricle, so the two circulations run in parallel. For the baby to stay adequately oxygenated before corrective surgery, there must be mixing between the two circuits. This mixing happens at natural openings like the patent foramen ovale (in the atrial level) and the patent ductus arteriosus (between the great arteries). Keeping these openings open allows some blood from the two circuits to mix, delivering more oxygen to the systemic circulation. Prostaglandin E1 is often used to keep the ductus arteriosus patent until surgery. Closing the PDA would reduce mixing and worsen cyanosis, and relying only on pulmonary circulation would not sustain systemic oxygenation. An arterial switch is the definitive operation, but maintaining mixing before surgery is essential, which is achieved by keeping the PDA and PFO open.