How can persistant pulmonary htn can cause differential cynosis

Reading File

Finding Sources

Searching PubMed

pulmonary hypertension AND Eisenmenger

Searching the Web

differential cyanosis persistent pulmonary hypertension mechanism ductus arteriosus

In persistent pulmonary hypertension of the newborn (PPHN), pulmonary vascular resistance remains abnormally high after birth. Therefore, blood from the right ventricle cannot easily enter the lungs for oxygenation.

If the ductus arteriosus remains patent, pulmonary artery pressure may exceed aortic pressure, causing a right-to-left ductal shunt:

Pulmonary artery → patent ductus arteriosus → descending aorta

This sends relatively deoxygenated blood into the descending aorta, which supplies the lower body.

The right arm and head receive blood from the ascending aorta, before the ductus enters the aorta, so they are relatively better oxygenated. This is called preductal blood.
The legs and lower body receive the deoxygenated ductal blood after it enters the descending aorta, so they are more cyanosed. This is called postductal blood.

Thus, there is differential cyanosis: the right hand is pinker / has a higher SpO₂ than the feet. A preductal-postductal saturation difference of about 5% or more supports this finding. The right hand is used because the left subclavian artery can arise near the ductal insertion and may not reliably be preductal.

If right-to-left shunting occurs mainly across the foramen ovale, both upper and lower body receive mixed blood, so cyanosis is usually generalized rather than differential. MSD Manual's PPHN explanation describes this preductal versus postductal pattern.

This is a shared conversation. Sign in to Orris to start your own chat.