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Thread: A-a gradient

  1. #1
    manleyjb's Avatar
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    A-a gradient

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    An 18 year old male is brought to the University of Utah Emergency Room after being found unconscious in his dorm room in a pool of his own vomit. He has a history of depression and recently expressed feelings of despondency to some of his friends. An empty pill bottle is found on the floor beside him. A blood gas obtained on room air at the start of his resuscitation is as follows: PaO2 44, PaCO2 60, pH 7.36, HCO3 24. Which one of the following diagnoses is most consistent with these values?

    A. Aspiration of gastric contents from obvious vomiting
    B. Pulmonary embolism from prolonged immobility
    C. Hypoventilation from drug induced ventilatory suppression
    D. Pneumonitis in response to drug overdose


    The explanation says that the A-a gradient is normal. Assuming 760 torr and FiO2 of .21, I cannot get the A-a gradient to come out to a normal number, which is supposed to < 10 torr.

    Anyone have an idea? I didn't have a hard time with the answer, but I do with the explanation. Thanks for the help.




  2. #2
    MD999 is offline Senior Member 510 points
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    Quote Originally Posted by manleyjb
    An 18 year old male is brought to the University of Utah Emergency Room after being found unconscious in his dorm room in a pool of his own vomit. He has a history of depression and recently expressed feelings of despondency to some of his friends. An empty pill bottle is found on the floor beside him. A blood gas obtained on room air at the start of his resuscitation is as follows: PaO2 44, PaCO2 60, pH 7.36, HCO3 24. Which one of the following diagnoses is most consistent with these values?

    A. Aspiration of gastric contents from obvious vomiting
    B. Pulmonary embolism from prolonged immobility
    C. Hypoventilation from drug induced ventilatory suppression
    D. Pneumonitis in response to drug overdose


    The explanation says that the A-a gradient is normal. Assuming 760 torr and FiO2 of .21, I cannot get the A-a gradient to come out to a normal number, which is supposed to < 10 torr.

    Anyone have an idea? I didn't have a hard time with the answer, but I do with the explanation. Thanks for the help.



    Answer is C.
    It'd be a Respiratory Acidosis due to the hypoventilation from the drug (prob an opiate). I dont think that your explanation makes a lot of sense. Which question set did you get that from?

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    manleyjb's Avatar
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    Question

    Quote Originally Posted by MD999
    Answer is C.
    It'd be a Respiratory Acidosis due to the hypoventilation from the drug (prob an opiate). I dont think that your explanation makes a lot of sense. Which question set did you get that from?
    I agree C is the answer. It was actually a fairly easy question to answer. The issue I have was the explanation given does not make any sense. I guess it could be incorrect. The explanation says the A-a gradient is normal which eliminates the other 3 answer choices. I answered it based only on the interpretation of the gases. Thanks for your help.

  4. #4
    Unregistered Guest
    i guess they want to you to know that aspiration of gastric content functions as an airway obstruction where ventilation is 0 and V/Q=0 (SHUNT), and pulmonary embolism, where there is ventilation but not perfusion, is a dead space V/Q= infinite. so the only one with a normal A-a would be hypoventilation, but again they dont say it. you have to dig into the question. that's what i think

  5. #5
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    wouldn't pH be alot lower with that kind of CO2 ?

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    stevecwood is offline School Official 510 points
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    A-a question

    you know it's hypoventilation because the definition of hypoventilation is elevated PCO2. If R is assumed to be 0.8, the alveolar PO2 = PIO2 - PaCO2/.8 = 150 - 60/.8 = 150 - 75 = 75 mmHg. so the A-a is within the normal range.
    The pH should be much lower with a PCO2 of 60 and normal bicarb, so that part of the question is poorly written and the pH is impossible.

  7. #7
    Unregistered969 Guest
    What if the pt is a retainer thus baseline with an eleveated Co2?

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