Ductal shunt ABG guidance: for ductal shunt, ABG should be drawn on which side to measure PaO2 reaching the head?

• A. Right side
• B. Left side
• C. Umbilical artery
• D. Carotid artery

Answer: (A)

In ductal shunt situations, you want to know the oxygen level reaching the brain, so you sample arterial blood from a site that best represents the blood feeding the head. The right upper body is supplied by the brachiocephalic trunk, which gives rise to the right common carotid and right subclavian arteries. Blood traveling to the head largely comes through these right-side vessels, making a right-sided ABG (for example, from the right radial artery) the best reflection of cerebral PaO2 in this scenario. Left-sided samples can be influenced by different arch-flow patterns, and umbilical artery blood reflects systemic fetal blood rather than cerebral oxygenation. While carotid sampling would directly reflect brain oxygenation, the practical and most representative choice in ductal shunt situations is a right-side arterial sample.