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NBME 21 Answers

nbme21/Block 4/Question#33 (54.7 difficulty score)
A female newborn delivered at 26 weeks' ...

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submitted by hyoscyamine(57),
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FA gp 271. oTo cumh eoangxonyit acn uaesc eefr ldicraa gmedaa lgadeni to irtytoehnap fo rypmetirtau

mmm21  Okay i might be retarded, but why i can’t understand that they r asking about the thing that is damaged ? 😂😂 +5  
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? +2  
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? +2  
burak  they didn't give the patient fio2 100%, question asks the reason for it. but in a very stupid way +30  
naught  Supplemental O2 may also cause bronchopulmonary dysplasia or intraventricular hemorrhage (germinal matrix, located in subventricular zone NOT choroid plexus) +1  
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. +  
soccerfan23  In other words....the question is basically asking why they gave the patient a fio2 of 92-95% instead of 100%. The reason is because 100% oxygen would lead to retinopathy of prematurity. The lower 92-95% oxygen levels protect the retina from damage. The wording of the question sucks tho imo. +2  
randi  FA 2019 p210 under Free radical injury examples +  

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")

+5/- beanie368(21),

submitted by mcl(618),
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coic"hrn hihg yonxeg otusnsiatra acn aeslyrdev acffet nugl and eey eoutosmc fo rrpeetm s.if"t naniknl

submitted by divya(63),
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gaeer ihtw ka ryet.rub'eh gtirny ot asy ttah ipmyrar aolg fo mnrteteta wthi napmlpleuets 2o is to kema uesr rtehe is no nertlia agadme.

submitted by ergogenic22(348),
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wyh si tocpetrino fo eth ioodrch xpel,su mfro tvianerrulintacr euutrpr ecnoysdra ot glirmean mitaxr mroeehgarh nto a posbesli w?nears

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. +  
burak  choroid plexus is different than germinal amtrix +  
meryen13  retinal hemorrhage is more common that IVH even if you think that it could damage choroid places secondary to germinal matrix hemorrhage. +  

submitted by lilmonkey(20),
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nAenoy iaergnd stih ouieqnst