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acid-base status question:

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by GingerSue GingerSue (Member) Member

GingerSue has 20 years experience .

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I thought that I understood, but now a question appears:

my manual says that the body is compensating for an imbalance if PCO2 and HCO3 are changing in the same direction.

my textbook says that if the parameter that does not match the pH is moving in the opposite direction, then the body is attempting to compensate.

I am trying to figure out an example in which the pH is 7.35, the PCO2 is 48 and HCO3 is 27

my manual says that 7.35 is acidosis (textbook says that below 7.35 is acidosis and 7.35 to 7.45 is normal)

I've been searching for some better explanations on google, but haven't yet found one that clearly explains

thanks if anyone can help

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That is compensated resp acidosis. If you can find an article call Making ABGs as easy as ABC or Making ABGs childs play. I can not remember the exact name, but it gives a really good break down. It teaches you the tic-tac-toe method. Once you get it. it will all be so much clearer.

The PH is on the acid side with the PcO2 and Hco3 is alk because it is compensating. I hope that helps. Jess

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GingerSue has 20 years experience.

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thanks for the link

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I got these analogies from an old nurse article that deals with ABG:

Ok, so you are given the pH, C02, HC03 in a problem.

You know that the normal range of ABG is as follows:

pH: 7.35-7.45

C02: 35-45 (just remember the values is just like pH without the 7.)

HC03: 22-26

Think of respiratory acidosis/alkalosis as a seesaw between pH and C02:

If pH goes down and C02 goes up it's respiratory acidosis

If pH goes up and C02 goes down it's respiratory alkalosis

Think of metabolic acidosis/alkalosis as an elevator between pH and HC03.

If pH goes up and HC03 goes up it's metabolic alkalosis

If pH goes down and HC03 goes down it's metabolic acidosis

*Both pH and HC03 have to go the same direction

I hope this helps!

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GingerSue has 20 years experience.

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thanks

I don't have a problem understanding the way

to think through respiratory acidosis or alkalosis,

or metabolic acidosis or alkalosis.

the compensation is what I'm trying to understand,

as explained by two different sources, that seem

to confuse me:

so, just to repeat:

my manual says that the body is compensating for an imbalance if PCO2 and HCO3 are changing in the same direction.

my textbook says that if the parameter that does not match the pH is moving in the opposite direction, then the body is attempting to compensate.

and, what is the accepted definition of acidosis (or rather 7.35):

I am trying to figure out an example in which the pH is 7.35, the PCO2 is 48 and HCO3 is 27

my manual says that 7.35 is acidosis (textbook says that below 7.35 is acidosis and 7.35 to 7.45 is normal, but my textbook say 7.35 - 7.45 is = slightly alkaline)

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Megsd is a BSN, RN and specializes in Neuro.

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Here's how I learned compensation (man I hope I don't get this twisted around). If the pH is normal and the CO2 and HCO3 are abnormal, the body has compensated (because the pH is normal).

7.35 is within the normal limits, but it is at the acidic end of normal, so it's compensated acidosis. (If the pH were any lower, it'd be full-blown acidosis).

The pH is low and the CO2 is high, so it's respiratory in origin. The HCO3 is becoming raised (creating more base) in an attempt to compensate for the acidosis.

Hence you have compensated respiratory acidosis.

As far as: "if the parameter that does not match the pH is moving in the opposite direction, then the body is attempting to compensate". That definition is confusing to me. The other makes more sense. I guess it means in this situation that the HCO3 (base) doesn't match the pH (7.35 - acidosis) and is going up (becoming more basic). Which kind of goes along with what I said earlier.

Hope that helps any.

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GingerSue has 20 years experience.

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we are trying, thanks

it's that my manual says that 7.35 is acidosis, but the textbook says that 7.35 - 7.35 is slightly alkaline.

in the eg. that I've included, with pH at 7.35 (considered acidosis by the manual), the HCO3 is rising, so this would be in the same direction as the PCO2 which is elevated (with the range in the manual of 21 - 26), and the direction of the HCO3 - is it opposite to the direction of the pH? (according to the manual, the pH of 7.35 is acidosis so that is decreasing and the HCO3 at 27 is just above the normal range so it is increasing). So the HCO3 is rising like the PCO2 is already elevated. This is the same direction. But the HCO3 is moving in the opposite direction of the pH. Am I off track?

Just trying to understand the explanations that are provided.

The manual explanation says "if the PCO2 and HCO3 are moving in the same direction" (same as what: each other?)

But the textbook says " if the parameter that does not match the pH is moving in the opposite direction then the body is attempting to compensate"

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6,372 Posts; 34,635 Profile Views

Here's how I learned compensation (man I hope I don't get this twisted around). If the pH is normal and the CO2 and HCO3 are abnormal, the body has compensated (because the pH is normal).

7.35 is within the normal limits, but it is at the acidic end of normal, so it's compensated acidosis. (If the pH were any lower, it'd be full-blown acidosis).

The pH is low and the CO2 is high, so it's respiratory in origin. The HCO3 is becoming raised (creating more base) in an attempt to compensate for the acidosis.

Hence you have compensated respiratory acidosis.

As far as: "if the parameter that does not match the pH is moving in the opposite direction, then the body is attempting to compensate". That definition is confusing to me. The other makes more sense. I guess it means in this situation that the HCO3 (base) doesn't match the pH (7.35 - acidosis) and is going up (becoming more basic). Which kind of goes along with what I said earlier.

Hope that helps any.

Meg is right on the money.

Just one more hint to make interpretation easier: While 7.35-7.45 is considered a normal range for pH, it is easier to interpret lab results if you use 7.40 as the norm. No range for purposes of interpretation. If the pH is less than 7.40, you have acidosis. If the pH is greater than 7.40, you have alkalosis. Then look at your CO2 and HCO3 values to determine whether the pH shift is caused by respiratory or metabolic changes, and to determine whether there is any compensation.

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GingerSue has 20 years experience.

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seems that there will be some sources that say 7.35 is acidosis and some sources that say it is slightly alkaline.

It's interesting that the textbook explains that if the pH drops below 7.35 then the person has acidosis, even though the blood may never become truly acidic.

next it'll be review of compensation,

to understand which is same direction or which is opposite direction

(because the manual says same and the textbook says opposite)

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Megsd is a BSN, RN and specializes in Neuro.

723 Posts; 5,905 Profile Views

seems that there will be some sources that say 7.35 is acidosis and some sources that say it is slightly alkaline.

It's interesting that the textbook explains that if the pH drops below 7.35 then the person has acidosis, even though the blood may never become truly acidic.

next it'll be review of compensation,

to understand which is same direction or which is opposite direction

(because the manual says same and the textbook says opposite)

I don't know why they say the blood would be slightly alkaline, because that value is on the acidic end of normal. The suggestion Jolie had for using 7.40 as normal is a good one for this.

As far as the conflicting compensation definitions, I don't think you're reading them right. They're not actually conflicting -- they're talking about different values. You said...

my manual says that the body is compensating for an imbalance if PCO2 and HCO3 are changing in the same direction.

The two values they are comparing are the PCO2 and the HCO3. In the example you provided, the CO2 is high, and the HCO3 is also high, so the body is compensating. Both values are moving in the same direction (as each other, yes).

my textbook says that if the parameter that does not match the pH is moving in the opposite direction, then the body is attempting to compensate.

The two values they are comparing are the pH and whatever value doesn't match the pH (in your example, this is the HCO3). This is also true because the pH is low and acidic, and the HCO3 is high and basic. These two values are moving in opposite directions, so the body is trying to compensate by making more base to counteract the extra acid from the extra CO2, thereby raising the pH to within normal limits.

Both definitions are true, they are just describing two different aspects of the compensation.

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