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Why do we check both pre- and post-ductal saturations in cardiac babies?
To detect shunting across the ductus arteriosus and see if there's a difference in oxygen delivery to the upper vs lower body
Why is it concerning when pre-and post-ductal saturations differ by more than 10% in ductal dependent systemic circulatiom?
It means the difference in DO2 to the upper & lower body is ↑ : PH/high PVR, restrictive/closing pda (systemic), flow to lungs < systemic
Where are pre- and post- ductal probes placed?
Pre= right hand and post= either foot. Right hand = flow to brain, feet= lower body
When do babies need the PDA to stay open? (think blood flow not specific defect)
When it provides critical pulmonary circulation or systemic circulation - depends on defect
What is a ductal-dependent pulmonary lesion?
A defect where blood cannot reach the lungs without a PDA. The PDA must stay open to let blood flow from the aorta into the PA's
What drug keeps the ductus open?
Prostaglandin E1 (PGE)
What is a ductal-dependent systemic lesion?
A defect where blood can't reach the body without the PDA. Blood flows from PA--> PDA--> Aorta--> systemic circulation
What does the right-hand probe tell you?
pre-ductal oxygenation -- blood going to the brain.
What does the foot probe tell you?
Post-ductal oxygenation -- blood after ductal mixing to the body.
Pre: 97% and post: 87% -- what type of shunt?
Right-to-left through the ductus. Blood bypasses the lungs --> lowers post ductal sats.
Pre 85%, Post: 92% -- what's happening here?
Reverse differential cyanosis. Oxygenated blood is reaching the lower body but not the upper body/brain
For a pt w/ pulmonary atresia, what clinical signs appear first if the duct starts to close?
Rapid desaturation and worsening cyanosis
In a ductal-dependent pulmonary lesion, is pre- or post- ductal sat usually lower?
Often both are low -- equal cyanosis
What happens if the PDA closes in a systemic lesion?
Shock, acidosis, weak pulses, cool extremities.... bad things
Your patient becomes agitated. Their pre: 96% and post sat drops into the 80s. Why?
Right-to-left shunting through the PDA. PVR rises= pressure in the PA > the pressure in Aorta
