Assessment of pre-ductal O2 saturation in PDA of a 3 minute born infant is done at?

- Preductal & postductal oxygen saturation parameters are used to detect R - L shunt at the level of foramen ovale & ductus aeriosus. - Pre - ductal O2 saturation in PDA: Always seen in RIGHT UPPER LIMB supplied by Right Subclan aery- itself a branch of BRACHIOCEPHALIC TRUNK (branch of arch of aoa). It is not near to ductus aeriosus. So, no mixing of Pre or Post ductal blood. - Left hand is supplied by LEFT SUBCLAN AERY Just distal to left subclan aery is the ductus aeriosus. So, mixing of Pre and Post ductal blood can take place - Therefore, right upper limb is always considered for Pre-ductal O2 saturation. - Lower limbs are considered for post-ductal O2 saturation - Preductal O2 saturation of at least 3% above the postductal is evidence of right-to-left ductal shunting