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NBME 22 Answers

nbme22/Block 2/Question#21

A newborn has cyanosis, tachypnea, and retractions ...

Respiratory acidosis and metabolic acidosis

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submitted by privwill(3),

Step by step:

  1. pH = low = acidosis
  2. HCO3 = low = acidosis
  3. CO2 = high = acidosis

So, what I've learned is that, in essence, metabolic acidosis always takes priority in these scenarios. It's evident that the person is not compensating, but you want to calculate anyway by using Winter = 1.5 (HCO3) + 8 .
If you calculate you will see that the expected is 30.5.

  1. If CO2 is higher than expected = concomitant respiratory acidosis
  2. If CO2 is lower than expected = concomitant respiratory alkalosis

Here it is higher than expected (65) so concomitant respiratory acidosis.

I guess if you wanted to start with the respiratory acidosis you would've taken into consideration that bicarbonate should've gone up to compensate. It didn't so it's uncompensated. Not sure if there's a formula to calculate the other stuff

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submitted by armymed88(13),

A little math here.. pH is low --> acidosis pCO2 is high --> respiratory Normal compensation should be roughly a 1 (acute) to 4(chronic) increase in bicarb per every 10 increase in pCO2.. Its lower here, so clearly not compensated and indicated additional drop in bicard --> add on metab acidosis

hello  Hm, what do you mean by "normal compensation?" Are you talking about the bicarb should be increased? Are you saying that a normal compensation would be metabolic alkalosis? Would metabolic alkalosis be an increase in bicarb? +1  
kateinwonderland  How do you know which one has bigger contribution in this situation where there's increased CO2 and decreased HCO-, both indicating acidosis?? +  
yb_26  normal kidney compensation would be an increase in bicarb reabsorption => increased serum bicarb. This pt has low serum bicarb => concurrent metabolic acidosis +