Board Review
You have a patient that comes into the ED with a chief complaint of AMS. The patient is found to be confused upon initial evaluation. The paramedics tell you that the patient's blood sugar was read as "hi" and they have a known history of insulin dependent diabetes. Vitals are: HR 130, BP 86/50, RR 18, T 98.6, Pulse Ox 95% on room air. You obtain labs including a VBG w/ lytes with the following findings:
K - 5.8
CO2 - 8
pH - 7.16
pCO2 - 28
How would you interpret this acid/base disturbance?
A. Metabolic acidosis with appropriate respiratory compensation
B. Metabolic acidosis with respiratory acidosis
C. Metabolic acidosis with respiratory alkalosis
D. Respiratory acidosis with appropriate metabolic compensation
Correct answer is B - metabolic acidosis with respiratory acidosis. What is important to recognize for this patient is that their overall pH < 7.35 making them acidotic. Upon looking at the pCO2, it is lower than normal (35-45), which likely indicates hyperventilation and that the respiratory component likely is not causing the acidosis. From there, you see that the bicarbonate is 6 which is low (normal 22-28) which likely indicates a form of metabolic acidosis. In order to see if the patient is appropriately compensated, you will then need to use the Winter's Formula which is: Expected pCO2 = (1.5 * bicarbonate) + 8 +/- 2. In this patient, that gets: expected CO2 = (1.5 * 8) + 8 +/- 2 = 18 - 22. Given that our patient's measured pCO2 is 28, there is an associated respiratory acidosis in addition to patient's metabolic acidosis.
Burger MK, Schaller DJ. Metabolic Acidosis. [Updated 2021 Jul 26]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK482146/