HELP with ABGs and Correction by Ventilatory Settings - page 2

by nursingitup9 3,577 Views | 12 Comments

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... Read More


  1. 2
    Quote from core0
    Umm if you can't get the PaO2 above 100 on an NRB then yes the P:F ratio would apply to them.
    PF ratio is normally calculated while on a ventilator. But, to show my point, some COPD patients and others with long term pulmonary disease do not oxygenate well. It would probably take a ventilator and a high FiO2 to get some to 100 mmHg on a good "normal" day. That does not mean they have ARDS or need ECMO. You also have to take into consideration other factors which can lower the PaO2.

    This is also why hyperoxic and shunt studies are done in PFT labs on high risk patients prior to major surgeries. The patient is placed on 100% O2 via closed system for 20 - 30 minutes. Baseline and end time ABGs are drawn. BTW: They did not go apneic during this time.


    Quote from core0
    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.
    SIMV consider of a mandatory VT breath and a PS breath setting. If the patient is breathing spontaneously the PS breath is utilized. Some really don't understand this breath setting and may set it as low as 5 cmH2O or what some used to call "compensating for the tube" which leaves no or little support for the rest of the breath. This is great for a SBT to have 5/5 in a pure PSV mode for 20 minutes for extubation criteria but not for acute lung injury. Others will pull out some number like 10 without knowing why other than just because that is what we always use. You see this on CCT/Flight teams a lot. Often this gives a VT of about 100 or less and only increases the work of breathing. However, if you are doing a Plateau Pressure and catch the PS breaths, you will get a Plateau of 10 or 15 or somewhere inbetween depending on flow termination. This is why when you look at the vent documentation on computer charting you will see Plateau Pressures all over the map, especially if nurses are also doing them, because they weren't paying attention to the graphics and the breath delivered. This mode also causes asynchrony due to variations of flow patterns and how much PS is given which makes the reading erratic. I don't know of many still using this mode except in NICU (neonatal) but then that is a whole different set of reasons as to why it is used there.


    Quote from core0
    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.
    You should NOT have to assume about the blebs. That is what CXRs are for. Chances are this pt may also have had a CT Scan in their records.

    What you are referring to for PEEP and FiO2 is finding optimal PEEP which can be done utilizing the graphics before just pulling a lot of unnecessary ABGs.

    Mild, Moderate and Severe are degrees determined by PFT studies with the percentages noted such as FEV1 and FVC. It does not always determine oxygenation. There are many COPD patients who are determined by testing to be Severe by ATS or GOLD but are not requiring home oxygen. People with severe COPD are not always CO2 retainers either.

    Those with severe obstructive disease is why there are different ventilator modes, mucolytics/airway clearance devices and even heliox. For oxygenation there is nitric oxide and other vasodilating drugs. It is not always just the lungs creating these issues.

    Before jumping fully into a full ARDSnet assumption, deal with some of the factors associated with Sepsis such as raising the MAP of the BP. Improve the circulation and cardiac output along with oxygen utilization (ScO2, SvO2). Get the lactate trending lower. Perfuse the kidneys. Once these things turn around, the pulmonary status will also. You can still use basic lung sparing principles but there may not be a need to do a full ARDSnet press.

    ARDS is also one of the more misunderstood diagnoses. It is either way over diagnosed unnecessarily before pertinent clinical data is in or under diagnosed and under treated by some conservatives. I think there was another thread recently which was a good illustration of that.

    However, the bottom line is still don't over treat the ventilator until you have treated the patient.
    Last edit by TraumaSurfer on Oct 29, '13
    Susie2310 and Esme12 like this.
  2. 1
    Quote from core0
    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.
    Actually the US has been utilizing CPAP and BIPAP for several decades for longer periods of time.

    Either CPAP or BIPAP would have been better than just a 28% VM in this situation.

    Some will start with CPAP if the patient is breathing rapidly to allow the pt to synch with the flow while the airways are being supported with some positive pressure. The may then ease the patient into BIPAP or some other mode depending on the technology being used. "BIPAP" is no longer your grandma's machine. The new machines are quite sophisticated and can do may things for patient comfort and avoid intubation.
    Susie2310 likes this.
  3. 0
    Quote from ktliz
    Whoops, meant BiPap.
    Either CPAP or BIPAP might be utilized. See my above post for an explanation.


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