pH Acid Base question

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I hope that I can make this simple. Here are the numbers. pH = 7.38, HCO3 = 30, PCO2 = 53.

I have a teacher that says that this is Metabolic Acidosis w/ Full compensation, but I have read in books that it is Respiratory Acidosis w/ Full compensation. Both of these have high HCO3 and PCO2 in the books--the only thing different is where the pH lies. They state that it has to be an acid problem because the pH is lying a little on the acidic side. They say that the body will not overcompensate on pH and that this 7.38 shows you which side that the pH started from, an acidic situation. Thank You, Doug

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Specializes in Nurse Scientist-Research.

This is a very typical blood gas, you will see this very often in chronic lung patients. COPD's, infants with BPD. Compensated respiratory acidosis. Compensated acidosis evidenced by pH low side of normal, respiratory evidenced by PCO2 above 45, the HCO3 highish at 30. It's not uncommon with really bad compensated resp patients to see HCO3's 35+

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This is a concept many people struggle with. Remember the following:

A normal PH RANGE is 7.35-7.45

A normal PH is 7.40

So, when considering compensation and underlying problems, always consider what side of 7.40 you PH is indicating.

Unfortunately, your teacher is incorrect. With a metabolic acidosis, the bicarbonate would be low. In this gas it is elevated. An elevated bicarbonate with a PH of less than 7.40 suggests an underlying respiratory acidosis with compensation. The elevated CO2 confirms the said suggestion. Your book is also correct in that the body rarely overcompensates.

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I am so sorry, but I misquoted what the teacher said. She said that it was Metabolic ALKALOSIS w full compensation. When I look in my book, it shows that Met Alk and Resp Acid have the same high HCO3 and PCO2, but the difference is where the pH lies. She says that it could be either one and that even if the pH is at 7.38, it could be Metabolic Alkalosis. Thanks again, Doug

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I just worked it out and I got compensated respiratory acidosis... I was told that the greater the difference is the problem system, so the pco2 is more abnormal, so you have a respiratory disorder.

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Specializes in Cardiac Care.

I've never heard of that. I'm not saying your instructor is wrong, but I do disagree. The respiratory mechanism (PCO2) is seriously elevated, and the pH is on the acidic side of normal. I guess I'm not clear on why your instructor is certain that the acidic pH is really a metabolic alkalosis compensation...

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Now that is the question, some say that you might go with which one is greater, but my book says that the body will never over-compensate for pH, therefore whichever side of 7.4 that the pH is on will tell you wherther it is Resp Acidosis or Metabolic Alkalosis. Of course this is for full compensation situations. Is anyone sure?

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It is true that you can have respiratory compensation for a metabolic alkalosis. However, as stated the body rarely overcompensates. Therefore, if the underlying deficit was a true metabolic alkalosis, the PH would be between 7.41-7.45. In this case, it is 7.38. To have a metabolic alkalosis with respiratory compensation with this blood gas, you would need overcompensation. As stated, overcompensation is very uncommon. Therefore, your teacher would generally be incorrect, say for a few strange situations.

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Thanks guys, she got very defensive when asked. Fly

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Sometimes the best thing to do is to let things go. I am having similar situations occur as a RN who is currently back in school and going through an allied health program. My big mouth and tendency to argue...er...discuss the finer points of some concepts has not won any favor with my instructors.

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Specializes in Nurse Scientist-Research.

Clinical correlation is always helpful, but not usually available in test questions like this. But of the body's compensatory mechanisms, I can't recall ever seeing a patient hyPOventilate to raise their CO2. They can hyPERventilate to blow off CO2, and their kidneys can let go of extra HCO3 or retain more of it. But I've never known or heard of a patient whose body hyPOventilates to correct metabolic alkalosis.

I have seen infants that have compensated pH's, their CO2's running 55-70, their HCO3's running 35+. Their CO2's are attributed to chronic lung disease and their high HCO3's are attributed to both body's compensatory mechanisms and d/t side effects of certain diuretics given for their chronic lung disease.

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Specializes in None.

Yeah, its hard. From the beginning, she has picked her favorites, and treated many of us as nothing, just shy of being out of line. I am not sure why she picked teaching. Thanks again

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