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ABG Interpretation...Not The Norm

Posted

Hi All,

Lowly student here with the results of an "expanded" ABG lab study and I have no clue what I am looking at beyond pH, PCO2, HCO3 and am hoping someone can clarify.

Specimen type: Arterial

pH: 7.41

pCO2: 36.8

pO2: 224.6 (High)

ABG HCO3: 22.7

ABG O2 Sat Cal/Meas: 99.5

ABG Base Excess: -1.5

ABG Hemoglobin: 12.2

ABG Oxyhemoglobin: 69.40 (Low)

ABG Carboyhemoglobin: 0.3

ABG Methemoglobin: 0.6

Allen Test: N/A

Sodium: 124.3 (Low)

Potassium: 4.3

Vent Mode: AC

Vent Rate: 14.00

FiO2: 100

Tidal Volume: 450

PEEP or CPAP: 10

Unless indicated labs are normal, the patient is on a TP vent. I am aware the last five items are related to the vent and vent settings, I included them for reference and a bit of background.

By all tense and purposes the ABGs are "normal". Patient may be hyperoxygenated based on the pO2? Not sure though and any insight would be appreciated.

Cheers.

Edited by CodeBrownQueen
Forgot type of draw.

You are correct about the *blood gas* values (pH, PaCo2, PaO2, SaO2, HCO3, base excess) being normal other than the PaO2 showing hyperoxygenation. The other components are not part of a standard ABG but are either additional lab values or information entered to reflect the respiratory status of the patient.

Different facilities have different lab equipment at their disposal (either at the point of care or in the lab) that can allow them to run the same ABG and obtain additional lab values. One such device is the iSTAT; it allows bedside testing of ABGs and also provides values for other labs. Where I work, our iSTATs provide electrolyte and blood sugar results in addition to the ABG results. They can be configured differently to include other labs and there are more than likely other devices on the market that work similarly (I'm only familiar with the iSTAT).

I forgot to include: the sample is arterial.

You didn't need to include that - that's what the "A" in ABG stands for (ARTERIAL blood gas). Results from a venous blood gas are VBGs. ;)

Hi VB,

Forgive the severe truncation :wacky:. Based on your knowledge, and the values presented, are you familiar with what the abnormalities indicate? Or is there some kind of standardized algorithm like the *blood gasses* (pH, PaCo2, HCO3) for determining the respiratory status?

The high PaO2 is a direct result of the 100% O2 being delivered to the patient via the vent (the PEEP is also a *strong* factor in oxygenation; mode, rate, and tidal volume will also affect oxygenation). In terms of the oxyhemoglobin, I found a good article that you can take a look at here. The values of oxy/carboxy/met-hemoglobin are not normally included in standard blood gas studies. The low sodium is unrelated to the patient's respiratory status.

Kuriin, BSN, RN

Specializes in Emergency. Has 4 years experience.

Where I work, our iSTATs provide electrolyte and blood sugar results in addition to the ABG results.

I believe you mean VBG. You would not get an ABG from venous, nor will it be read in an iStat.

I believe you mean VBG. You would not get an ABG from venous, nor will it be read in an iStat.

What? iStat cartridges work with venous or arterial blood for electrolytes, glucose, and BGs.

Kuriin, BSN, RN

Specializes in Emergency. Has 4 years experience.

Weird. We never did ABG with our iStats in the ED.

AJJKRN

Specializes in Medical-Surgical/Float Pool/Stepdown. Has 6+ years experience.

Weird. We never did ABG with our iStats in the ED.

Pts in our ICUs usually have arterial lines in place to draw off of.

Kuriin, BSN, RN

Specializes in Emergency. Has 4 years experience.

I actually just remembered there is an option for Arterial and Venous before inserting the cartridge. My mistake!

Esme12, ASN, BSN, RN

Specializes in Critical Care, ED, Cath lab, CTPAC,Trauma. Has 40 years experience.

Normal values:

PH = 7.35 - 7.45

C02 = 35 - 45

HC03 = 21-26

Respiratory acidosis = low ph and high C02

hypoventilation (eg: COPD, narcs or sedatives, atelectasis)

*Compensated by metabolic alkalosis (increased HC03)

For example:

ph 7.20 C02 60 HC03 24 (uncompensated respiratory acidosis)

ph 7.33 C02 55 HC03 29 (partially compensated respiratory acidosis)

ph 7.37 C02 60 HC03 37 (compensated respiratory acidosis)

Respiratory alkalosis : high ph and low C02

hyperventilation (eg: anxiety, PE, pain, sepsis, brain injury)

*Compensated by metabolic acidosis (decreased HC03)

examples:

ph 7.51 C02 26 HC03 25 (uncompensated respiratory alkalosis)

ph 7.47 C02 32 HC03 20 (partially compensated respiratory alkalosis)

ph 7.43 C02 30 HC03 19 (compensated respiratory alkalosis)

Metabolic acidosis : low ph and low HC03

diabetic ketoacidosis, starvation, severe diarrhea

*Compensated by respiratory alkalosis (decreased C02)

examples:

ph 7.23 C02 36 HC03 14 (uncompensated metabolic acidosis)

ph 7.31 C02 30 HC03 17 (partially compensated metabolic acidosis)

ph 7.38 C02 26 HC03 20 (compensated metabolic acidosis)

Metabloic alkalosis = high ph and high HC03

severe vomiting, potassium deficit, diuretics

*Compensated by respiratory acidosis (increased C02)

example:

ph 7.54 C02 44 HC03 29 (uncompensated metabolic alkalosis)

ph 7.50 C02 49 HC03 32 (partially compensated metabolic alkalosis)

ph 7.44 C02 52 HC02 35 (compensated metabolic alkalosis)

*Remember that compensation corrects the ph.

Now a simple way to remember this......

CO2 = acid, makes things acidic

HCO3 = base, makes things alkalotic

Remember ROME

R-Respiratory

O-Opposite

M-Metabolic

E-Equal

Ok always look at the pH first...

pH

pH>7.45 = alkalosis

Then, if the CO2 is high or low, then it is respiratory...If the HCO3 is high or low then it is metabolic. How you remember that is that the respiratory system is involved with CO2 (blowing air off or slowing RR), and the kidneys (metabolic) are involved with HCO3 (excreting or not excreting).

Here is how you think thru it: pH = 7.25 CO2 = 40 HCO3 = 17

Ok, first, the pH is low so think acidosis. CO2 is WNL. HCO3 is low. Draw arrows if it helps. The abnormal values are both low (think Equal). Metabolic imbalances are equal. So, this must be metabolic acidosis!

Now, for compensation...If you have a metabolic imbalance, the respiratory system is going to try to compensate. Respiratory = CO2. If the CO2 is normal in the ABG, then there is no compensation going on. Compensation in acidosis will decrease the CO2 because you want to get rid of the acid (CO2). In alkalosis, it will increase because you want to add more acid (CO2)

If you have a respiratory imbalance, the kidneys will try to compensate. Kidneys = HCO3. If the HCO3 is normal in the ABG, then there is no compensation going on. Compensation in acidosis will increase HCO3 because you want to hold on to the base to make it more alkalotic. In alkalosis, it will decrease because you want to excrete the base to make it more acidic.

Here.I.Stand, BSN, RN

Specializes in SICU, trauma, neuro. Has 16 years experience.

Can definitely come down on the FiO2, and possibly the PEEP as well, depending on why it was set that high. (Standard PEEP is 5, more if the pt needs more to oxygenate or keep those alveoli recruited.) The RRT is an excellent resource, and I usually ask if they have a recommendation which to turn down 1st. But definitely with the FiO2 as high as it can go, with that pO2 it can be reduced

Thank you, this was for a case study and careplans. I'm just in LPN school but if it's abnormal we have to discuss/cover it. I wasn't going to be on the floor again before it was due. These results were given on the last day of clinicals/school for the week.

meanmaryjean, DNP, RN

Specializes in NICU, ICU, PICU, Academia. Has 40 years experience.

OP: It's 'for all intents and purposes'.

Good discussion!