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NBME 21 Answers

nbme21/Block 4/Question#33

A female newborn delivered at 26 weeks' gestation ...


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FA pg 217. Too much oxygenation can cause free radical damage leading to retinopathy of prematurity

mmm21  Okay i might be retarded, but why i can’t understand that they r asking about the thing that is damaged ? πŸ˜‚πŸ˜‚ +2  
sahusema  Seriously! The question says "the goal of treatment is the protection of which of the following structures?" If too much O2 damages the retina, how is this treatment supposed to be protective to the retina? +  
ratadecalle  I think too much oxygen would be with the ventilator having a high FiO2 setting, which they don't mention here but I'm guessing thats the thing they're controlling to avoid oxygen toxicity? +1  
burak  they didn't give the patient fio2 100%, question asks the reason for it. but in a very stupid way +9  
naught  Supplemental O2 may also cause bronchopulmonary dysplasia or intraventricular hemorrhage (germinal matrix, located in subventricular zone NOT choroid plexus) +  
fkstpashls  92-95% isn't high, but it's enough to get everything else oxygenated. Because it's not 100% high flow the retinas don't over-vascularize and lead to damage/hemorrhage, and shit like that. +  

Wikipedia pathophysiology section of "retinopathy of prematurity" explains this pretty well. Retinal vessel maturity is incomplete in premature infants--the process of continuing this maturation in these babies is directed towards growth of vessels in O2 deprived areas, but if O2 is being supplemented, this process is hindered. Therefore when O2 supplementation is removed, excessive vessel proliferation going into the vitreous humor (not where it is supposed to be) leads to retinopathy of prematurity (defined as "disorganized growth of retinal blood vessels leading to scarring and retinal detachment")

+/- beanie368(6),

 +1  upvote downvote
submitted by mcl(375),

"chronic high oxygen saturations can adversely affect lung and eye outcomes of preterm infants." link

 +0  upvote downvote
submitted by divya(28),

agree with burak. they're trying to say that primary goal of treatment with supplemental o2 is to make sure there is no retinal damage.

 +0  upvote downvote
submitted by ergogenic22(121),

why is protection of the choroid plexus, from intraventricular rupture secondary to germinal matrix hemorrhage not a possible answer?

whoissaad  yes same question, both retinopathy and intraventricular hemmorage can occur due to high oxygen levels.. +  
cienfuegos  I mistakenly chose choroid plexus too, based on wiki seems this is most common cause of IVH in term infants: IVH in the preterm brain usually arises from the germinal matrix whereas IVH in the term infants originates from the choroid plexus. However, it is particularly common in premature infants or those of very low birth weight... Most intraventricular hemorrhages occur in the first 72 hours after birth. The risk is increased with use of extracorporeal membrane oxygenation in preterm infants. https://en.wikipedia.org/wiki/Intraventricular_hemorrhage#Babies +  
burak  choroid plexus is different than germinal amtrix +