HELP with ABGs and Correction by Ventilatory Settings

  1. 0
    In a patient with a history of COPD who comes into the hospital and is diagnosed with Acute Respiratory Failure and pneumonia...

    ABG 1: CO2 54, HCO3 30, O2 52, pH 7.25. Pt is given 28% with a venturi mask.
    ABG 2 30 minutes later: CO2 48, HCO3 30, O2 58, pH 7.42

    Based on these results, the patient is intubated.

    2 hours after intubation, mode SIMV at 14, 50% FIO2, TV 750, and 5 PEEP:
    pH 7.30
    PO2 60
    PCO2 64
    HCO3 30

    I realize these results are not what is expected after 2 hours on the vent. The pH is still acidic, the O2 is low, the PCO2 is high and acidic, and the HCO3 is increased and trying to compensate.

    My question is....What ACTIONS would you take to correct this ABG? Would you increase the RR? Increase the FIO2? Increase the PEEP? I would imagine you wouldn't increase the tidal volume? What else? THANKS!
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  4. 12 Comments so far...

  5. 0
    Quote from nursingitup9
    In a patient with a history of COPD who comes into the hospital and is diagnosed with Acute Respiratory Failure and pneumonia...

    ABG 1: CO2 54, HCO3 30, O2 52, pH 7.25. Pt is given 28% with a venturi mask.
    ABG 2 30 minutes later: CO2 48, HCO3 30, O2 58, pH 7.42

    Based on these results, the patient is intubated.

    2 hours after intubation, mode SIMV at 14, 50% FIO2, TV 750, and 5 PEEP:
    pH 7.30
    PO2 60
    PCO2 64
    HCO3 30

    I realize these results are not what is expected after 2 hours on the vent. The pH is still acidic, the O2 is low, the PCO2 is high and acidic, and the HCO3 is increased and trying to compensate.

    My question is....What ACTIONS would you take to correct this ABG? Would you increase the RR? Increase the FIO2? Increase the PEEP? I would imagine you wouldn't increase the tidal volume? What else? THANKS!
    Think about ventilation and oxygenation separately. While this is an over simplification, ventilation (CO2 exchange) is a function of minute ventilation which is made up of tidal volume and rate (rate x tv = minute ventilation). Oxygenation is controlled by PEEP and FiO2 (%oxygen). So if you want to increase oxygenation you increase FiO2 or PEEP. If you want to increase ventilation you increase rate or tidal volume.

    http://www.nursingcenter.com/lnc/static?pageid=1030183

    U
    nfortunately its more complicated. What is your plateau pressures, does the patient have ARDS?

    Presuming the patient has ARDS (PF ratio < 300 and bilateral pulmonary infiltrates) I would increase the rate and decrease the TV to 8cc/kg ideal body weight. I would bump up the PEEP to 8 or 10 and wean FiO2.

    http://www.ardsnet.org/system/files/Ventilator%20Protocol%20Card.pdf

  6. 0
    hmmm i wonder what his O2 were before...
    i don't know, FiO2 50% for a patient with pneumonia seems low to me.
  7. 1
    Let's look at the whole picture here rather than just the knobology.

    Quote from nursingitup9
    In a patient with a history of COPD who comes into the hospital and is diagnosed with Acute Respiratory Failure and pneumonia...


    This tells you there is probably a V/Q mismatch.



    Quote from nursingitup9
    ABG 1: CO2 54, HCO3 30, O2 52, pH 7.25. Pt is given 28% with a venturi mask.
    Based on the clinical information of ARF and PNA, why is this person only on a 28% VM? Is the old "only give 2 LPM regardless of distress" in play here? If a person is in distress, give oxygen to relieve their discomfort. The next ABG sums up my statement.

    Quote from nursingitup9
    ABG 2 30 minutes later: CO2 48, HCO3 30, O2 58, pH 7.42
    You have a PaO2 appropriate for oxygen of 1 - 2 L in a COPD patient but he is obviously struggling since there is a pH of 7.42. True COPD patients who are retainers rarely if ever raise their pH above 7.42 unless they are "hyperventilating" from a PE or having the needle poking the radial artery or bone during the arterial stick, some metabolic disorder or THEY ARE IN PROFOUND distress. In this situation it would be the withholding of oxygen on a hypoxic patient with a known PNA and Acute Respiratory failure.

    Quote from nursingitup9
    Based on these results, the patient is intubated.
    The second set of ABGs were great especially if he want only on 28% O2. What probably bought him the tube was his clinical presentation of "I am about to die because I can not get enough oxygen". Hence the V/Q mismatch and 28% VM.

    Not getting enough oxygen leads to pulmonary vasoconstriction and pulmonary hypertension. COPD patients may also have Cor Pulmonale. This brings us to the ventilator.

    Quote from nursingitup9
    2 hours after intubation, mode SIMV at 14, 50% FIO2, TV 750, and 5 PEEP:
    pH 7.30
    PO2 60
    PCO2 64
    HCO3 30
    First, SIMV in Acute Respiratory Failure? What was the Pressure Support? Was it really adequate for someone in Acute Respiratory Failure? You would probably have to nearly match his VT given by the ventilator which with a new PNA, that would have to have been a PS of about 30 cmH2O. What was his plateaus which might have been difficult at best to get.

    Quote from nursingitup9
    I realize these results are not what is expected after 2 hours on the vent. The pH is still acidic, the O2 is low, the PCO2 is high and acidic, and the HCO3 is increased and trying to compensate.
    Why do you think the HCO3 is trying to compensate? What was the anion gap and the CO2 on the CMP or Chem Panel? If the lungs are in a severe chronic state, this person might very well be a CO2 retainer which means he lives with an HCO2 of 30.

    Another reason for the increase in PaCO2, other than a poor ventilator mode choice, is the deadspace from the pulmonary vasoconstriction from a prolonged hypoxic state. This is what is not used to explain a sudden increase in PaCO2 rather than the old "knocked out his hypoxic drive".

    What are some of the other reasons he could be acidotic? Lactate? Anion Gap? Infection? Dehydration?


    Quote from nursingitup9
    My question is....What ACTIONS would you take to correct this ABG? Would you increase the RR? Increase the FIO2? Increase the PEEP? I would imagine you wouldn't increase the tidal volume? What else? THANKS!
    Again you will need to look at the whole picture including the CXR.
    How tall is this person? You will need that to determine the appropriate weight to calculate the tidal volume.

    What else has been done? What are his vital signs? Is he hyper or hypotensive? What is his lactate? Urinary output? These all should play a huge part in determining your ventilator course. Does the CXR show unilateral or bilateral disease process? Air follows the path of least resistance. Any blebs or signs of hyperinflation? How do his labs look? Is he dehydrated? How old is he? Any other disease processes? What about sedation? Ventilator synchrony? Has a central line been place and is there CVP monitoring?

    Ventilator management is much more than turning a couple of knobs. You have to management the patient.
    Last edit by TraumaSurfer on Oct 28, '13
    Spoiled1 likes this.
  8. 0
    Quote from core0
    http://www.nursingcenter.com/lnc/static?pageid=1030183

    U
    nfortunately its more complicated. What is your plateau pressures, does the patient have ARDS?

    Presuming the patient has ARDS (PF ratio < 300 and bilateral pulmonary infiltrates) I would increase the rate and decrease the TV to 8cc/kg ideal body weight. I would bump up the PEEP to 8 or 10 and wean FiO2.

    http://www.ardsnet.org/system/files/Ventilator Protocol Card.pdf

    The patient has a history of COPD. We do not know his age or his CXR. If the person can not get their PaO2 above 100 mmHg on a good day and a NRB mask, what makes you think this ratio would apply to them?

    Plateau pressures on a COPD patient in SIMV may also be misleading.

    As far as PEEP, again, gotta know the CXR and many other factors which I mentioned in my other post. Bilateral infiltrates do not always mean ARDS and may be more of a sepsis pathway. Don't go cranking on the knobs until you considered the data, options and corrected or in a place to start correcting. Crank the PEEP and you tank the BP along with blowing a bleb or two will get you nowhere fast.

    Consider the whole patient and all the disease processes you will be treating.
  9. 1
    Yeah, I don't get the venturi mask. Wouldn't this patient immediately buy themselves CPAP? And hopefully not need to be intubated?

    (I'm a fairly new critical care nurse who relies heavily on my respiratory therapists!)
    TraumaSurfer likes this.
  10. 0
    Why not bipap first, instead of the venturi or the vent. Were the gases really that bad for a history of COPD?
  11. 0
    Quote from ktliz
    Wouldn't this patient immediately buy themselves CPAP?
    Whoops, meant BiPap.
  12. 0
    Quote from TraumaSurfer
    The patient has a history of COPD. We do not know his age or his CXR. If the person can not get their PaO2 above 100 mmHg on a good day and a NRB mask, what makes you think this ratio would apply to them?
    Umm if you can't get the PaO2 above 100 on an NRB then yes the P:F ratio would apply to them.

    Quote from TraumaSurfer
    Plateau pressures on a COPD patient in SIMV may also be misleading.
    Can you explain this. We don't use much SIMV but the principle is similar to (S)CMV. You do an inspiratory hold at the designated TV and PEEP and you get a plateau pressure. Not sure how this would be misleading.

    Quote from TraumaSurfer
    As far as PEEP, again, gotta know the CXR and many other factors which I mentioned in my other post. Bilateral infiltrates do not always mean ARDS and may be more of a sepsis pathway. Don't go cranking on the knobs until you considered the data, options and corrected or in a place to start correcting. Crank the PEEP and you tank the BP along with blowing a bleb or two will get you nowhere fast.
    Actually one of my points was that you don't have enough information to make a judgement about how to manipulate the vent. As an exercise to demonstrate the relationship between PEEP and FiO2 and PaO2 it might work but its much more complex than given in the example. To use your example you are assuming all people with COPD have blebs. COPD is a continuum. Some patients have relatively mild COPD and relatively normal physiology. Some have horrible obstructive physiology and are a nightmare to ventilate. As for ARDS, ARDS and sepsis go hand in hand, or more appropriately ARDS and SIRS go hand in hand.

    Quote from TraumaSurfer
    Consider the whole patient and all the disease processes you will be treating.
    Good point. But again its unclear for the original statement what is going on. A lot of missing information.
  13. 0
    Quote from Do-over
    Why not bipap first, instead of the venturi or the vent. Were the gases really that bad for a history of COPD?
    It depends on the disease process. The OP stated the patient has PNA and acute respiratory failure with a history of COPD. I would agree that the gas wasn't that bad but if the patient was struggling and you weren't making headway the early intubation is probably the way to go. Generally BIPAP is a bridge therapy. For COPD the evidence is fairly compelling that you can bridge someone on BIPAP while aggressively treating their COPD. For other etiologies such as CHF the picture is more mixed. There are studies that show you can avoid intubation while you aggressively diurese. However, at least one study showed an increased incidence of MI in the BIPAP group vs intubation.

    In the OPs case since the stated diagnosis is PNA presumably its going to take more than 24 hours to turn around. While I agree that I wouldn't have necessarily intubated just based on the gas that was shown, if I thought the patient was going to decompensate further I would intubate early. A common mistake with BIPAP is that you continue as the patient worsens and you end up intubating on 100% with a sat of 90% which means you have no reserve if things don't go smoothly.

    On the other hand the Europeans are much more likely to use Bipap for longer periods of time as a rescue opposed to a bridge therapy.


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