The woes of acid base balance (please help!)

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Specializes in Trauma ICU.

So after getting my first MedSurg patient, I've been assigned to interpret her abnormal lab values. There are several different results I feel that may or may not be connected and I feel like the answer is right there in front of me. But I haven't figured it out quite yet.

The patient is a 27 y/o female who was in a motorcycle crash that gave her an open book pelvic fracture and fractured her right pubic symphysis. She had a Grade 4 spleen that was coiled twice and two pneumothoraxes upon admission. She is currently not on a chest tube and has a GCS of 15. She's awake alert and oriented but the most obvious of her problems is that she's maintained a consistent heart rate of 138 and she's got a fever running between 100 and 101 degrees Farenheit. She's also breathing between 25 and 35 respirations per minute so she's hyperventilating. Now here are my lab value issues...

Her blood CO2 is 32 mmol/L. If it was respiratory acidosis she should have low CO2 correct? She should be blowing off all the CO2 she has with her breathing as fast as it is but she's not. I'm thinking she has alkalosis of some kind which is consistent with her huge blood loss.

I was only able to get the abnormal lab values for that day but here's what I think has happened. She lost a large amount of blood with the initial crash (her RBCs and H&H show this, they're both low). As a result, her heart has been working faster since her admission (which was on 9/1/09). As a result of the initial blood loss I think her kidneys responded and the renin angiontensin aldosterone system was put into overdrive. By producing aldosterone she would have retained her sodium and thus as much of her total body volume as she could.

In keeping all the volume she would have retained hydrogen and bicarbonate. But as I'm reading my lab values book I see that chloride serves as a buffer with acid base balance. If there's enough hydrogen and bicarbonate in the extracellular space (which turns to CO2...hence the high value) chloride goes back into the cell. So would that show up as hypochloremia? She doesn't have very low chloride but it is outside the normal range of values.

I feel like I'm making this bigger than it needs to be. And I still haven't gotten to the low calcium (which was critical upon her admission). If anyone can give me guidance that would be great. Thanks!

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Are you getting these numbers of an ABG? if so what were the other values (pH, Bicarbonate, PaO2, potassium, calcium, etc)

Because what may actually be happening is a fluid balance problem.

In respiratory acidosis you would have a low pH, elevated PaCO2, low PaO2, elevated potassium, and variable bicarbonate levels.

In respiratory alkalosis you would have High pH, Low bicarbonate levels, Low PaCO2, low serum potassium, and low serum calcium.

If she did in fact loose circulating volume and there is no infection that can be causing the fever she has three of the signs of dehydration: Increased HR, Increased Respiratory Rate, Fever.

It may be a fluid volume deficit. Look at the whole picture not just one lab value.

I may be wrong so see what others have to say.

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Her blood CO2 is 32 mmol/L. If it was respiratory acidosis she should have low CO2 correct? She should be blowing off all the CO2 she has with her breathing as fast as it is but she's not. I'm thinking she has alkalosis of some kind which is consistent with her huge blood loss.

CO2 is acidic so a high PaCO2 could indicate acidosis. We really need more information then this to figure it out. She could be alkalytic and her PaCO2 is up because she is compensating. If you provide the rest of her ABG numbers I'm sure we could help more.

Having a massive trauma does crazy things to your body and all of this, plus the surgery could easily increase your body's metabolic rate, increasing your temp, resp rate and heart rate...although I agree that it does sound like a bit much. I would keep a keen eye open for signs and symptoms of infection, she is a prime candidate for sure.

Edited to add...

Alright, I feel I may lead someone astray and I don't want to...

I don't think CO2 is actually an acid but when it is dissolved in blood it reacts thusly:

H20 + CO2 --> H2CO3 --> H + HCO3

releasing the Hydrogen ion and therefore increasing the acidity. Increasing your rate and depth of breathing will "blow off" CO2 and cause the reaction to shift to the left, therefore decreasing the acidity.

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Specializes in Trauma ICU.

Her WBC count is definitely elevated- its 27. She also has an abdominal wall hematoma so I'm thinking that's playing a part. Her staples around her surgical wound are clean though so if there's infection (and I think there may be with the fever) its not outwardly presenting.

But I didn't have her ABG levels, these are the only abnormal ones I could find. I wish I did, really because I feel like this tiny bit of information is part of the problem. But her CO2 level if you notice isn't in mmHg so I don't think its an ABG, this CO2 level is part of a BMP.

Does this help? I agree I don't have everything to go on. I'm just looking to see if I'm on the right track. Other than what I've mentioned though nothing else on her chart is indicated as abnormal.

EDIT: Her calcium is 7.5 (I believe the units are mg/dl) and I know enough that her RBCs and H and H are deeefinitely low. Everything else is in normal range (that I have access to).

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Specializes in OB, MS, Education, Hospice.

I would need more info & some assessment findings to be sure, but did you consider a fatty emboli? If the CO2 level was from a BMP, the level is actually high--which supports your idea regarding respiratory acidosis. Check out this link--

http://emedicine.medscape.com/article/460524-overview

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