Hi everyone,

I am quite new to this forum but I really lik ehow the forum and site works. Although it seems quite silly but I need to understand the basics of pre and post ductal saturation what do they actually measure! Blood from the heart or to the heart? Thanks guys!

Cardiovascular plumbing , that's one of my favourite topics!

The pre- and the post-ductal saturations are both arterial saturations (blood from the heart), and refers to arterial oxygen saturation in vessels originating from the aorta before and after the ductal orifice in the aorta.

Classically, the pre-ductal values are recorded in the right hand, but one can argue that left-handed saturations are roughly the same (http://www.biomedcentral.com/content/pdf/1471-2431-10-35.pdf).

Arterial post-ductal sat's are measured in the foot.

Post-ductal saturations become lower than pre-ductal when there is mixing of pulmonary blood through the duct, i.e. in congenital heart defects that are duct dependent. For example, severe coarcations or transpositions of the great arteries typically have lower postductal sat´s.

This is the theoretical background to POX screening (http://www.bmj.com/content/338/bmj.a3037.full)

Pre-ductal and post-ductal pulse O2 saturation (SpO2) monitors (to detect R → L

shunting at ductus arteriosus). A difference of ≥10% suggests marked pulmonary

hypertension or PDA dependent leison.

Pre-ductal and post-ductal pulse O2 saturation (SpO2) can be used as screening for cyanotic heart disease for NB befor discharge hom fro postnatal ward.

In the strange scenario of post ductal SpO2 being more than the Pre-ductal SpO2, think of TGA with PPHN.

Thank you very much ...That was very helpful! Things will make sense now.

I wonder if there are any more common states where you would find reversed pre- and postductal saturations? We see it sometimes and those children do not have serious congenital heart defects such as TGA. Right now I´m looking at one baby with 95% foot 86% right hand.

Any experience on this?

We do see sometimes such reversed pre/post ductal saturations in our NICU in children without any heart defect. It is usually below 5%.

Unfortunately I haven't find any explanation yet.

Thank you for your feedback! I am not alone 😊 

On 2/23/2019 at 5:11 AM, Urban Rosenqvist said:

I wonder if there are any more common states where you would find reversed pre- and postductal saturations? We see it sometimes and those children do not have serious congenital heart defects such as TGA. Right now I´m looking at one baby with 95% foot 86% right hand.

Any experience on this?

I know this is not what you mean, but the single most common cause of this phenomenon in my experience is actually reversal of the probes (ie the pre- and post- are mislabeled/swapped).

 

But, yes, I have seen several cases of the actual physical phenomenon you describe, often self resolved in a short period of time and sometimes causing an annoyed call from a cardiologist asking why I got an ECHO

Can we diagnose PPHN fairly confidently by this procedure to start Sidenafil

bimc

On ‎3‎/‎13‎/‎2019 at 6:37 AM, bimalc said:

I know this is not what you mean, but the single most common cause of this phenomenon in my experience is actually reversal of the probes (ie the pre- and post- are mislabeled/swapped).

 

But, yes, I have seen several cases of the actual physical phenomenon you describe, often self resolved in a short period of time and sometimes causing an annoyed call from a cardiologist asking why I got an ECHO

Good point though. I will check for mislabeled/swapped probes in the future... 

i would like to answer Dr Bachy about the reversed pre-post ductal pulse oximetry 

The most important is to focus on the PPHN; those cases not only seen in TGA but also in aortic arch interruption or CoA and they only represent less than 1% of the PPHN 

so very very very rare

I see it frequently in otherwise healthy babies..the reassuring sign: the postductal saturation is 95-100% in those babies with very well felt femorals.

It happened that most of those babies where somehow polycythaemic ( Hb around 200mg%)

Also if you do echo..likely the duct will be still open ( transitional).

If you check the Saturations pre and post few times a day (baby is healthy and feeding) you will  see the difference decrease and likely to normalize around day3.

I still have no physiological explanation.