The preferred site for preductal pulse oximetry is which location?

• A. Right Upper Limb
• B. Left Upper Limb
• C. Lower Limb
• D. Ear Lobe

Answer: (A)

Preductal pulse oximetry is meant to measure oxygen saturation in blood before it passes through the ductus arteriosus. The right upper limb is the preferred site because its arterial supply comes from the brachiocephalic trunk, which branches off the aortic arch proximal to the ductus arteriosus. This means the right hand reflects preductal systemic arterial oxygenation, making it the best site to screen for ductus-dependent or left-to-right shunt lesions. Measuring in the left upper limb or lower limbs would reflect postductal blood after potential mixing through the ductus, which can hide or confound true preductal oxygenation. The ear lobe is not routinely used due to reliability issues like perfusion and measurement variability.