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NBME 22 Answers

nbme22/Block 2/Question#6

A 52-year-old man is brought to the emergency ...

4 Months

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It was just asking the lifespan of RBCs (120 days)

haliburton  If I'm reading this right, this is just a tricky dicky question. I think CO binds 200x stronger than O2. But if an O2 cycles through binding / unbinding 200 times before a CO gets kicked off, this should still clear the CO from that cell sooner or later. strange to think it is 1. essentially permanently trapped in a cell, and 2. doesn't kill you and can be treated with O2 to resolution within a few hours or a day. They must just be thinking, until that last RBC dies, you've got original CO in a circulating cell. but just a fraction (because you didn't die). not sure how that CO isn't just passed on during recycling, based on this line of thinking. +3  
link981  The question while stupidly written, asks how long the RBC's that carry the CO take to be removed from the circulation, not how long the CO takes to be removed from the RBC. Just asking the lifespan of RBCs in an stupidly complicated way. As we know, RBC's life span is about 120 days and then they are removed from our circulation. 120 days is about 4 months. Next time they will probably ask weeks or in hours, who knows? smh +2  




 +2  upvote downvote
submitted by iviax94(6),

I figured they were trying to get at the life expectancy of an RBC, but wouldn’t supplemental O2 technically replace the CO bound to RBCs? FA even mentions that CO binds competitively to RBCs, and isn’t that the whole point of giving hyperbaric/100% O2?

nc1992  First aid has a lot of errors +  
yotsubato  Thats not an error though. Thats the actual reason behind giving hyperbartic O2 for CO poisoning... +  




 +2  upvote downvote
submitted by link981(35),

The question while stupidly written, asks how long the RBC's that carry the CO take to be removed from the circulation, not how long the CO takes to be removed from the RBC. Just asking the lifespan of RBCs in an stupidly complicated way. As we know, RBC's life span is about 120 days and then they are removed from our circulation. 120 days is about 4 months. Next time they will probably ask the RBC lifespan in weeks or in hours, who knows? smh