Analyze the question stem and focus on the numbers
Rephrase the question in your own words, noting the cues and assessments given
- We are dealing with an older client with a history of emphysema.
- The client reports fatigue, confusion, and headache.
- Respiratory rate of the client is 26 breaths per minute.
- The client is suspected of having respiratory acidosis.
What do you know about the cues, numbers, and findings in the stem?
- History of emphysema tells us this older client has COPD.
- Emphysema leads to inefficient gas exchange in the lungs, and can lead to respiratory acidosis, which the client is suspected to have.
- The reports from the client are abnormal (fatigue, confusion, headache) and can be symptoms of respiratory acidosis, which the client is suspected to have.
- Respiratory rate of 26 breaths per minute is higher than normal and fits the suspicion of respiratory acidosis.
Tip: All the cues that are given in the question stem are confirmations of the suspected diagnosis of respiratory acidosis. Therefore, when you move on to the answer choices, only focus on the diagnosis of respiratory acidosis. This is what the question asks you to do: Match the correct answer choices to this condition.
What are arterial blood gas values?
An ABG looks at three values:
- pH: normal pH is between 7.35 and 7.45
- CO2: normal CO2 is 35 to 45 mm Hg
- Bicarbonate: normal HCO3 values are about 22–26 mEq/L (some references are a bit higher).
Imbalances in these values can lead to four forms of acid–base imbalance that can be diagnosed based on characteristic patterns of too-high and too-low ABG values:
- Respiratory acidosis
- Respiratory alkalosis
- Metabolic acidosis
- Metabolic alkalosis
Systematically approach the answer choices
Before you look at each answer individually, sum up again what kind of answers you are presented with here:
- You have a PO2 value, a PCO2 value, a HCO3 value, and two different pH values.
- Between one and all of them can apply to the patient described in the stem.
- Your task is to decide for each one individually if it fits the condition of the patient in the stem: respiratory acidosis.
A. PaO2 of 72 mm Hg
Normal PaO2 is 75 or 80–100, so this value is considered low.
Emphysema means air is trapped in the alveoli, leading to poor gas exchange and decreased PaO2. A low PaO2 would be expected for a client with respiratory acidosis, so this answer would be correct.
B. PaCO2 of 48 mm Hg
Normal PaCO2 is 35–45, so this value is high. The trapped air in the alveoli due to emphysema decreases the removal of CO2. Not getting rid of enough CO2, having too much of this acid in the blood, would increase PaCO2 and push the client toward acidosis – so, this answer fits the client and is correct.
C. pH of 7.31
A normal pH is 7.25 to 7.45, so this number is lower => more acidic. Since in respiratory acidosis, a lower pH is to be expected (due to the high PaCO2), this answer fits as well and is correct.
Tip: Don’t let yourself get thrown off by what feels like “too many” or “too few” correct or incorrect answers in a row. Our need for balance does not work in our favor in select-all-that-apply questions! Look at each answer choice separately and decide confidently based on this only, ignoring the number of answer choices you may have already marked correct or incorrect. Remember: Only one may be correct, or all of them!
D. HCO3 of 20 mEq/L
A normal bicarb is roughly 22 to 26, so 20 is not extremely low, but definitely on the low end. If a client is in respiratory acidosis, the body should be compensating with more base (bicarb is a base), so an at least normal, or elevated value would be expected. Therefore, this value does not fit respiratory acidosis and the answer is incorrect.
E. pH of 7.46
A pH of 7.46 is higher than the normal range of 7.35–7.45, which would result in alkalosis, not acidosis. Acidosis decreases the pH. This answer choice is incorrect.
Recap
Double-check your reasoning on all the answers and take care none of them are contradicting each other. Again, don’t be fooled by thinking “I should probably choose one more/less.” Trust your judgment!
