NBME 22 Increased blood HCO3− (NBME Answers)

NBME 22 Answers

nbme22/Block 2/Question#27 (reveal difficulty score)
A 50-year-old man who has smoked 2 packs of ...
Increased blood HCO3− 🔍 / 📺 / 🌳 / 📖
tags:

+11 upvote downvote
submitted by ∗armymed88(49)

get full access to all content ⋅ pick a username

emphysema leads to CO2 trapping leading to increase paCO2 in the blood, which gives you a respiratory acidosis Proper renal compensation will increase bicard reabs and decrease excretion- giving you increased bicarb in the blood

get full access to all content ⋅ pick a username

meningitis Increased blood HCO3 could have easily been interpreted as increased blood pH aswell. FOllowing your explanation, since the pt had acidosis, the increased HCO3 will just make it a normal pH. Another way to think of the question is: if there is decreased exhalation due to COPD --> increased CO2 --> increased CO2 transported in blood by entering the RBC's with Carbonic Anhydrase and HCO3 is released into blood stream. So increased CO2 -> increased HCO3 seeing as this type of CO2 transport is 70% of total CO2 content in blood. +27

drmohandes I thought you could never fully compensate, so your pH will never normalize. Primary problem = respiratory acidosis → pH low. Compensatory metabolic alkalosis will increase blood HCO3-, but not enough to normalize pH, it will just be 'less' low, but still an acidosis. +7

mtkilimanjaro I also think decreased blood PCO2 and increased blood pH are very similar (less CO2 in the blood means less acidic, pH could go up) therefore I ruled both of them out just from that +1

brise Aka this is the Bohr effect! +2

+2 upvote downvote
submitted by ∗waterloo(126)

get full access to all content ⋅ pick a username

if you also think, when someone has increased CO2 (as in this patient) they have respiratory ACIDOSIS right...so increased blood pH cannot be the right answer.

Also, compensatory mechanism for respiratory acidosis happens in three ways.

ECF: where due to mass action increase of CO2 leads to increase in H+ and HCO3- (but this is minimal - like 3%)
ICF: most of the buffering happens here with CO2 going into the cell.
Kidney: then over sometime, there will be some renal compensation (not correction) where the kidney will start to let go of H+ and reabsorb new HCO3 to help adjust pH towards normal.

get full access to all content ⋅ pick a username

+0 upvote downvote
submitted by usmlehulk(7)

get full access to all content ⋅ pick a username

can anyone please explain why option E which is increased in Urinary pH is not the correct answer. becasue hydrogen wasting is also a form of correcting respiratory acidosis.

get full access to all content ⋅ pick a username

wfma888 right- you will increase excretion of protons which will LOWER the pH! +2

an1 ↑ urine excretion of HCO3 (represents the alkaline pH/ higher pH) and ↑ urine pH are the same thing. Yes, you may wonder now why the ↑ blood HCO3 didn't cause an alkalosis but that's because the PRIMARY effect was the retention of CO2 leading to decreased blood pH +

an1 HCO3 is alkaline compared to H is what I meant to say ^ +

+0 upvote downvote
submitted by medjay7(5)

get full access to all content ⋅ pick a username

The easiest way I think of to see this is: 1) You are retaining a lot of CO2 2) The principal way in which we find CO2 in blood is as HCO3 3) You have a lot of HCO3

get full access to all content ⋅ pick a username

Must-See Comments from nbme22

sacredazn on Unrearranged immunoglobulin gene
seagull on Decreased binding of RNA polymerase
seagull on Anticholinergic
liverdietrying on Release of stored thyroid hormone from a ...
keycompany on Negative nitrogen balance
kernicterusthefrog on Displacement
mcl on Area labeled ‘D’
joha961 on Displacement
imgdoc on Area labeled ‘C’ (Abducens nucleus, right)
alwaysanonymous on 25 mL/cm H2O
drdoom on 1 in 600
seagull on Glutamine
bubbles on Acute retroviral infection
yotsubato on Phase variation