Acid-Base

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Hey there

So, I could really use some help. I can look at ABG values and in about 30 seconds tell you what the problem is with or without compensation or even partial...however I can't grasp this concept. Its not making sense. I dont even know whats not making sense. Its really frustrating. I read the material over and over and look at different books and more books and still nothing is settling in this head of mine...

Does anyone have any ideas on how to explain it all to me or a place I can read it or any suggestions at all.

Thank you.

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Where exactly are you in this? I know some things that might help but I need to know where you are. Do you know the basics? Sometimes it just takes one little piece of information to put the whole picture together.

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Specializes in Critical Care, Cardiothoracics, VADs.

i agree, if you can be a bit more specific i'd love to help. if you understand and can interpret abg's, you are doing pretty well so far!

here is a link i found searching this site:

http://www.ucsfhealth.org/childrens/health_professionals/manuals/19_acidbasebalance.pdf

(relates to babies but good info on causes and treatment of acid-base imbalances)

the best clinical teaching site i have ever found, great aussie website - all you need to know about fluid & electrolytes.. and more (maybe too much at this stage for you): http://www.anaesthesiamcq.com/acidbasebook/abindex.php

basically i would suggest we look at an example (nb this is how i remembered these things):

ph: 7.10

pco2: 70mmhg

po2: 75

hco3: 27

you need to know 3 basic things about this patient's acid-base status.

a) are they acidotic or alkalotic?

b) is it respiratory or metabolic in etiology?

c) is the patient coping/compensating or are they going to crash?

i'm going to ignore the po2 for this exercise.

step 1: look at the ph. is it high (alkalotic) or low (acidotic). i used a lot of red arrows when learning abgs! draw an up or down arrow next to the ph. in this case, it’s low, so they are acidotic.

step 2: look at the co2 - is it high (>45mmhg, acidotic) or low (

step 3: look at the bicarb - is it high (alkalotic) or low (acidotic)? again, if it is low they are going downhill and getting acidotic. it’s normal to minimally high in this case, so the patient is heading towards alkalosis.

à i would assume they have acidosis of respiratory etiology (copd, hypoventilation etc) and they are trying to compensate by increasing bicarb (but not there yet, since the ph is so abnormal). this patient has a severely bad ph drop, and they are not coping on their own, since they have not been able to increase their bicarb sufficiently to fix the ph. you need to treat the cause, and get the co2 down by increasing the rate and/or depth of ventilation. at this high of a co2, i'd assume the patient is almost unconscious, so they should be ventilated to drop the co2, which will also improve their mental status and ph.

tips:

1. i always remembered the ph effect by thinking that if they were acidotic, they got severely sick, very quickly ie. went downhill (just like their ph).

2. usually acid-base imbalances are caused by respiratory system in the short term, and renal (metabolic) system in the intermediate term. so you would expect an increase in co2 to lead to acidosis very quickly (minutes), after which the kidneys would try to adjust and increase the bicarb more slowly (hours).

3. ph under 7? going to heaven. bad sign to be so acidotic.

4. in general, acidosis is worse for you than alkalosis.

5. acidosis/alkalosis will screw up your oxygenation and electrolytes by moving ions in and out of cells abnormally to try and compensate. this is where you’ll hear about the hb-dissociation curve and whether it shifts left or right. all that means is that as you get more acidotic (lower ph, higher co2, lower temp), your hemoglobin will drop (disassociate from) its oxygen more readily. another reason you have trouble perfusing your tissues in acute acidosis. as you decrease the co2, warm the patient and raise the ph, the available oxygen is taken up better by the hemoglobin molecules (better o2 sat).

i hope this hasn’t been too “dumbed down” for you, just trying to keep it basic since i don’t know what level you’re at.

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Specializes in med/surg, telemetry, IV therapy, mgmt.

here are some links that you might find helpful:

http://www.acid-base.com/ - the home page of an interactive acid-base tutorial for medical students by professor alan grogono at tulane university, but there are things in it that are useful for nursing students. click on buttons throughout the presentation for more specific information. you might want to click on the "alphabetical index" at the left side to get a listing of the subjects covered on this site to save time. also, check out the "links" for more acid-base tutorial sites.

http://www.ekgusa.com/ceol/abgmap/abgindex.html - a ce offering on acid-base analysis of blood gas values. there is a pre-quiz and post quiz with explanations of metabolic or respiratory acidosis or alkalosis, combined and compensated. it is from ekg skillbuilders.

https://allnurses.com/forums/f199/easy-approach-acid-base-abnormalities-132845.html - good one page tutorial on acid-base balance

http://maagnursing.com/abg/ - this is an abg and acid/base balance tutorial. you do not have to register to go through the tutorial.

http://realnurseed.com/abg.htm - "abg's: it's all in the family"

http://www2.norwich.edu/mwalker/nr312/abg.htm - "interpretation of abgs: the battle of bicarb vs. carbon dioxide

http://www.the-abg-site.com/ - "the abg site". six easy steps to accurately interpret arterial blood gasses from ed4nurses.

http://web.indstate.edu/mary/abgdemo.html - an abg and abg analysis tutorial by a nursing instructor at indiana state university. http://www-isu.indstate.edu/mary/abgpract.htm - this is a quiz to test what you learned (includes answers).

http://www.rnceus.com/course_frame.asp?exam_id=18&directory=abgs - "interpretation of abgs: a four step method". from rnceus.com. discusses the authors four step method for interpreting abg values along with patient case studies and examples.

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Well today was a huge lecture on acid base. We went through:

The type of imbalance

Pathophysiology

Method of Compensation (if any)

Common causes and why

Major Signs and Symptoms

Nursing Interventions

For both Acute and Chronic resp/meta acidosis/alkalosis....WOW!

We went through in depth the exchanging of the + and - ions and so on....

And I thought I was confused yesterday? I am not sure if its confusion or just being really overwhelmed. I am having a hard time visualizing this stuff. Or I am not finding a way of putting it all together. I went to some of those websites already and have found some of it useful...I am DEFINITELY checking out the rest this evening while at least a little of this is fresh in my head. Any other tips you have now that you know where I am is great.

Thank you for your responses

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Okay...here for example:

A client, 5 days post-abdominal surgery, has a nasogastric tube. The nurse notes that the nasogastric tube (NGT) is draining a large amount (900 cc in 2hours) of coffee ground secretions. The client is not oriented to person, place, or time. The nurse contacts the attending physician and STAT ABGs are ordered.

The results from the ABGs come back from the laboratory and show:

pH = 7.52

Pa C02 = 35 mmHg

HC03 = 29 mEq/L

Once you have interpreted the ABG results, click on one of the following links

Compensated Respiratory Alkalosis

Uncompensated Metabolic Acidosis

Compensated Metabolic Acidosis

Uncompensated Metabolic Alkalosis

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Specializes in ICU/PCU/Infusion.

it's metabolic because it doesn't involve the respiratory system.

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Specializes in Critical Care, Cardiothoracics, VADs.

Kelli, given what you are learning, the info posted previously should help. Perhaps if you are overwhelmed you should study something else until you feel more relaxed.

You are exactly right with the last example: lots of acidic gastic drainage, the pH is rising to alkalosis, so the body has tried to compensate and excrete more acid/retain more base (HCO3) - hence the high bicarb level.

Don't worry about all the possible answers at the start, and coming up with an answer you then have to rationalize. Start by reading the case history and thinking about the patient and what makes sense. Do they have signs of anything in particular (you can memorize the signs and symptoms). Then just analyse pH, CO2, bicarb in that order.

You just have to know that the body tries to maintain a neutral pH. If something happens to mess it up, it tries to compensate with a different mechanism. It can increase/decrease respirations to remove/retain CO2, or it can increase/decrease H+/HCO3 ion secretion/retention.

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Metabolic because you are sucking gastric acid out through the NG tube.

It is a respiratory problem if it involves the respiratory system, everything else is considered metabolic.

We were taught that when the problem is metabolic that the respiratory system will try to fix it, and if the problem is respiratory that the kidneys will attempt to fix it. The lungs kind of stink at fixing things so the kidneys will help out too when it is metabolic. It makes sense, if something is wrong with your respiratory system it is comprimised and not going to be able to fix itself.

How did you know the difference between the two alkalosis choices?

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