Board Questions

1. A patient comes in with an acute asthma exacerbation and is tachypneic and wheezing. Their VBG results are: pH 7.45 PCO2 33 HCO3 22. How would you classify their acid base status?

a) Acute respiratory acidosis
b) Chronic respiratory acidosis
c) Acute respiratory alkalosis
d) Metabolic alkalosis with respiratory compensation

2. Your patient comes in with a three day history of polyuria and recent abdominal pain and vomiting. Their VBG results are: pH 7.13 PCO2 14 HCO3 5. How would you classify their acid base status?

a) Respiratory acidosis with concurrent metabolic acidosis
b) Metabolic acidosis with respiratory compensation
c) Metabolic acidosis without respiratory compensation
d) Respiratory acidosis with metabolic compensation

3. Your patient has an albumin of 2.0. How would you expect this to affect your calculation of her anion gap? 

a) Albumin does not affect anion gap
b) Falsely elevates the anion gap
c) Falsely decreases the anion gap
d) You would have to calculate the delta/delta ratio to know


ANSWERS & EXPLANATIONS

1. C. Your patient is in respiratory distress and is tachypneic. They have increased their alveolar minute ventilation and are in an acute respiratory alkalosis, as the pH is high and the PCO2 is low with a bicarbonate level that is essentially normal.

2. B. The patient has a metabolic acidosis with respiratory compensation, likely secondary to DKA. Your next steps are to determine the adequacy of compensation. Comparing the PCO2 and the last two digits of the pH, 14 and .13 respectively, it does appear compensation is appropriate. Similarly, Winter's formula calculates an expected PCO2 of 1.5(5) +8 +/-2= 13.5-17.5. Hence, this also suggests the respiratory compensation is appropriate and there is not another process occurring.

3. C Hypoalbuminemia leads to a false decrease in the anion gap. This is because albumin is negatively charged and when it is decreased, other negative anions such as Cl and HCO3 have to increase to maintain electroneutrality. As both Cl and HCO3 are included in the AG calculation, this would lead to a decrease in your anion gap, even if a significant anion gap acidosis (ie lactic acidosis or DKA) is occurring. Hence, the AG should be corrected in the setting of significant hypoalbuminemia. AGcorr= AG + 2.5(4-pt's albumin g/dl)


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