Post by Brian G on Nov 19, 2014 1:29:02 GMT
If you didn't read part one, do so now...
Arterial blood gases (ABG's)
We don't measure H+ ions directly though. We measure the pH, PaCO2, and HCO3-.
The normal values are:
pH 7.35-6.45
PaCO2 35-45 mmHg
HCO3- 22-26 mEq/L
Think of CO2 as an acid-more of it = more acidic.
Think of HCO3- as basic-more of it = more basic.
So, low levels of PaCO2 = more basic. High levels = more acidic.
Low levels of HCO3- = more acidic. High levels = more basic.
It kinda works in your head if you think when the HCO3- number goes down, so does the pH number. The PaCO2 goes in opposite directions. A lower PaCO2 number means a higher pH number.
Lab results
Say you get lab results that say the pH is 7.28, the PaCO2 is 65 mmHg, and the HCO3- is 24 mEq/L
The pH is below the normal range, so this is acidosis. It could be caused by a respiratory problem or a renal problem. And, if it is a respiratory problem, the kidneys will try to compensate. If it is a metabolic problem, the lungs will compensate. Treatment will depend on which system is having difficulties, so it is important to figure out which is the source. This is where the other two numbers come in.
Many ways to interpret the lab results. I think this way is easiest.
Step 1. Label all values as acidic, basic or normal.
If pH is <7.4, call it acidic. If >7.4 basic. Our results are 7.28, so call it acidic.
PaCO2 is 65 mmHg, so it is acidic
HCO3- is 24 mEq/L. This is within the normal range, so call it normal.
Step 2. Which matches the pH?
The PaCO2 does (they're both acidic). This is respiratory acidosis.
Step 3. Is the body compensating yet?
If the compensating value (HCO3- in this case) is still in the normal range, it hasn't done anything yet. This is uncompensated.
If the compensating value is outside the normal range, but the pH is still outside the normal range, it is trying to help out now but hasn't quite got there. This is partially compensated.
If the compensating value is outside the normal range AND the pH is now in the normal range, it has done it's job. This is compensated.
In our results, the HCO3- is normal, so we have uncompensated respiratory acidosis.
Another example...
pH 7.52, PaCO2 52, HCO3- 31
ph is high, so basic
PaCO2 is high, so acid
HCO3- is high, so basic
The HCO3- matches the pH, so this is metabolic alkalosis.
The PaCO2 is trying to help, but the pH is still out of range, so this is partially compensated metabolic acidosis.
That's it. Kinda longer than I meant, but I wanted to bring a lot of little points together.
For more examples, see next post.
Arterial blood gases (ABG's)
We don't measure H+ ions directly though. We measure the pH, PaCO2, and HCO3-.
The normal values are:
pH 7.35-6.45
PaCO2 35-45 mmHg
HCO3- 22-26 mEq/L
Think of CO2 as an acid-more of it = more acidic.
Think of HCO3- as basic-more of it = more basic.
So, low levels of PaCO2 = more basic. High levels = more acidic.
Low levels of HCO3- = more acidic. High levels = more basic.
It kinda works in your head if you think when the HCO3- number goes down, so does the pH number. The PaCO2 goes in opposite directions. A lower PaCO2 number means a higher pH number.
Lab results
Say you get lab results that say the pH is 7.28, the PaCO2 is 65 mmHg, and the HCO3- is 24 mEq/L
The pH is below the normal range, so this is acidosis. It could be caused by a respiratory problem or a renal problem. And, if it is a respiratory problem, the kidneys will try to compensate. If it is a metabolic problem, the lungs will compensate. Treatment will depend on which system is having difficulties, so it is important to figure out which is the source. This is where the other two numbers come in.
Many ways to interpret the lab results. I think this way is easiest.
Step 1. Label all values as acidic, basic or normal.
If pH is <7.4, call it acidic. If >7.4 basic. Our results are 7.28, so call it acidic.
PaCO2 is 65 mmHg, so it is acidic
HCO3- is 24 mEq/L. This is within the normal range, so call it normal.
Step 2. Which matches the pH?
The PaCO2 does (they're both acidic). This is respiratory acidosis.
Step 3. Is the body compensating yet?
If the compensating value (HCO3- in this case) is still in the normal range, it hasn't done anything yet. This is uncompensated.
If the compensating value is outside the normal range, but the pH is still outside the normal range, it is trying to help out now but hasn't quite got there. This is partially compensated.
If the compensating value is outside the normal range AND the pH is now in the normal range, it has done it's job. This is compensated.
In our results, the HCO3- is normal, so we have uncompensated respiratory acidosis.
Another example...
pH 7.52, PaCO2 52, HCO3- 31
ph is high, so basic
PaCO2 is high, so acid
HCO3- is high, so basic
The HCO3- matches the pH, so this is metabolic alkalosis.
The PaCO2 is trying to help, but the pH is still out of range, so this is partially compensated metabolic acidosis.
That's it. Kinda longer than I meant, but I wanted to bring a lot of little points together.
For more examples, see next post.