Where should you monitor the newborn's oxygen saturation?

• A. Right hand
• B. Left foot
• C. Right foot
• D. Ear

Answer: (A)

Measuring oxygen saturation in a newborn uses pulse oximetry to gauge how well oxygen is circulating. In newborns, blood can differ in oxygen saturation before and after passing through the ductus arteriosus, a fetal shunt. The right hand is the standard site for obtaining preductal saturation—that is, oxygen saturation before the blood mixes through the ductus into the systemic circulation. The right upper extremity is supplied by arteries that reflect this preductal blood, so it provides the most reliable measure of systemic oxygenation early in life.

If you used a sensor on the feet, you’d be measuring postductal saturation, which can lag or differ because the blood there has already mixed more with ductus-driven pathways. The ear is less reliable in newborns due to perfusion variability and potential measurement error.

So, the right hand is the best place to monitor newborn oxygen saturation to get preductal values.