Quote from Seagate
Ok I thought I understood metabolic/respiratory acidosis/alkalosis but the more examples I look at the more confused I get.
1) pH 7.35, PaCO2 66, bicarbonate 38, PaO2 70 = respiratory acidosis w/ complete compensation. And why is it respiratory instead of metabolic? Is it because of the low O2 value?
Now, it's complete compensation because both values, 66 & 70, are out of range correct?
2) pH 7.52 PaCO2 45, bicarbonate 36, PaO2 95 = Metabolic alkalosis w/o compensation.
I understand this example, the bicarbonate is too high, therefore its metabolic, but again, why is it without compensation? I thought full compensation was when the lungs or kidneys are able to correct for changes in pH when the other system is unable to and partial compensation was when the lungs or kidneys are unable to correct completely for pH change and the pH is not in normal range?
3) pH 7.55 PaCO2 24, bicarbonate 20, PaO2 95 = resp. alkalosis w/ partial compensation.
Ok, so in this example both the CO2 and the bicarbonate values are out of range,so why is it respiratory and not metabolic? And why is it partial compensation?
4) pH 7.28 PaCO2 24, bicarbonate 15, PaO2 95 = metabolic acidosis w/ partial compensation.
Again, I don't understand this one at all.
5) pH 7.35 PaCO2 24, bicarbonate 15, PaO2 95 = Metabolic acidosis w/ complete compensation.
This example is just like the one above, so basically the complete/partial compensation depends on the pH value?
By the way, I am getting these questions from my med/surge workbook by IGNAtavicius, chapter 19, p. 130.
Steps to interpreting ABGs:
1. Determine if the pH is acidotic or alkalotic based on the midpoint value of the range 7.35-7.45
. Therefore, anything below 7.4 would be considered acidotic and anything above 7.4 would be considered alkalotic.
2. Determine whether the determined acidotic/alkalotic state is caused by respiratory or metabolic issues. Which value matches the pH imbalance? CO2 changes reflect respiratory and HCO3 changes reflect metabolic.
The normal range for CO2 is 35-45
. CO2 is the acid
. So if the value is below 35, the person is losing CO2 from the body (through the respiratory tract), leaving a respiratory alkalotic state. If the CO2 is above 45, the person is retaining the acid CO2, causing a respiratory acidotic state.
The normal range for HCO3 is 22-26
. HCO3 is the base
. If the ABG value is below 22, the body is losing the HCO3 from the body (through the kidneys), leaving a metabolic acidotic state. If the HCO3 value is above 26, the body is retaining HCO3, causing a metabolic alkalotic state.
3. To determine if the body is trying to compensate, look at the other value that was not involved in your determination of respiratory or metabolic status. So if in step 2, you determined that the ABG represented respiratory acidosis, look at the HCO3 value. Is it out of its normal range? If it is the body is trying to compensate. Same goes for the CO2 if you determined that the cause of the state is metabolic.
4. To determine if the compensation is partial or complete, look back to the pH. If the pH is back in its normal range of 7.35-7.45, then the compensation is complete. If it is not, the compensation is partial.
Let's look at question #1:
pH 7.35, PaCO2 66, bicarbonate 38, PaO2 70
Step 1: Using the value of 7.4 as our desired pH, we find our given value on the acidotic side.
Step 2: PaCO2 is high. Retaining CO2 leads to acidosis. You can double check this by looking at the HCO3. Its value is 38, high. If the bicarbonate was the cause of the imbalance, the pH would be high indicating alkalosis, so we know the cause of the imbalance is respiratory acidosis.
Step 3: The bicarbonate is high. The body is trying to compensate.
Step 4: The pH is back within the normal range. Compensation is complete.
Hope this helps. Try it out on the other problems. Good luck.