ABGs come out to be an undifferentiated alkolosis....

  1. I have a question regarding ABGs on a patient I recently cared for.

    Admitted with bilateral PNA. Discovered to have minor CHF, minor ARF, and finally blood Cx's came back positive for strep.

    ABG results were as follows immediately after being placed on the Bipap machine due to respiratory fatigue- high likelihood of future intubation.

    pH 7.5H
    PCO2 34L
    HCO3- 27H
    PO2 75L

    How would one interpret this? Metabolic or respiratory alkalosis? I just don't know what to think. I'd have thought it'd have been more like metabolic acidosis given given the diagnoses.

    Thank you in advance if anyone can offer a clear explanation to me about this.
  2. Visit libran1984 profile page

    About libran1984

    Joined: Aug '11; Posts: 590; Likes: 685
    Registered Nurse; from US
    Specialty: 4 year(s) of experience in Emergency Nursing


  3. by   nurseprnRN

    If you remember that it takes 24 hours+ to retain extra bicarb in response to hypercarbia from COPD, but moments for some well-meaning person with a mechanical ventilation device to blow off CO2 retention, you have your answer. Betcha this guy had COPD before he got his pneumonia.

    This person has lowish oxygen ( you don't say whether he's on supplementation or not) but his alkalosis is due to his preexisting but now diminished chronic hypercarbia...which has been blown down to lower than usual levels (normal CO2 is 35-45) mechanically.

    If he were in a primary metabolic alkalosis, he'd be trying not to breathe much, to compensate that alkalosis by retaining CO2, but they aren't letting him (probably just as well, too).

    So, he has a mixed derangement with iatrogenic hypocarbia on top of a preexisting respiratory acidosis with metabolic compensation.

    Let me know if this doesn't make sense. It's a beautiful example of how we can overcompensate and how people get into trouble in the first place.
  4. by   libran1984
    I'm emailing you via all nurses.. should be getting something shortly for further clarification to make sure I got it.
  5. by   libran1984
    Oh! In addition to the email I sent you, wouldn't her PO2 have gone up after being put on the Bipap? Or do you think that it did and thus we are seing PO2 of 75?
  6. by   nurseprnRN
    If she has COPD she may have lost some oxygen-transport ability. Also, pna will do that to ya. Remember, your lung's first job is getting CO2 out because of its huge role in regulating pH; getting oxygen in is secondary.
  7. by   Esme12
    It's possible to have more than one disorder influencing blood gas values. For example ABG's with an alkalemic pH may exhibit respiratory acidosis and metabolic alkalosis. These disorders are termed complex acid-base or mixed disorders

    Common Laboratory (LAB) Values - ABGs - Arterial blood gases

    Respiratory Acidosis
    Acute < 7.35 > 45 Normal
    Partly Compensated < 7.35 > 45 > 26
    Compensated Normal > 45 > 26

    Respiratory Alkalosis
    Acute > 7.45 < 35 Normal
    Partly Compensated > 7.45 < 35 < 22
    Compensated Normal < 35 < 22

    Metabolic Acidosis
    Acute < 7.35 Normal < 22
    Partly Compensated < 7.35 < 35 < 22
    Compensated Normal < 35 < 22

    Metabolic Alkalosis
    Acute > 7.45 Normal > 26
    Partly Compensated > 7.45 > 45 > 26
    Compensated Normal > 45 > 26