ACID BASE SELF STUDY ANSWERS / RATIONALS:
Question 1:
A patient’s blood pH is decreasing. The nurse realizes that this patient’s hydrogen ion concentration is:
1. Increasing
2. Decreasing
3. Being affected by oxygen concentration
4. Stabilizing
Answer: 1
Rationale: As the hydrogen ion concentration increases, the pH decreases becomes more acidic.
Conversely, as the H+ ion concentration goes down, pH goes up, becomes more alkalotic. The hydrogen
ion is the smallest ionic particle and it is extremely reactive. The hydrogen ion combines with alkali/bases
or other negatively charged ions at low concentrations.
Question 2:
A patient is admitted with the diagnosis of diabetic ketoacidosis. The nurse realizes that this patient’s
body will attempt to attain acid-base balance by:
1. Decreasing its respiratory rate.
2. Increasing the reabsorption of hydrogen ions.
3. Increasing the secretion of hydrogen ions.
4. Decreasing the reabsorption of bicarbonate.
Answer: 3
Rationale: The main metabolic acids are lactic acid, pyruvic acid, ketoacids seen in diabetic acidosis, acetoacetic
acid, and beta-hydroxybutyric acid. These acids are eliminated by the kidneys or are metabolized by the liver.
The capacity for elimination of these metabolic acids is much lower than that of the lungs. In respiratory acidosis
and most cases of metabolic acidosis, the kidneys excrete hydrogen ion and conserve bicarbonate to correct the
pH. In order for the kidneys to excrete the hydrogen ions as urine it must first secrete the hydroden ion from the
blood. The kidneys secrete hydrogen ions and restore or reclaim bicarbonate to maintain acid–base balance.
Secretion is the active process of moving substances, such as hydrogen ions, from the blood into the tubular fluid
against the concentration gradient.

If substances remain in the tubular fluid (not get reabsorbed), they will eventually leave the body in urine.

If substances are reabsorbed from the tubular fluid back across the membrane and into the blood, they are
being reclaimed back into the body.
Therefore answer 3 is the best answer. Answers 1, 2, and 4 all increase the hydrogen ion in the blood and will
increase blood pH.
Question 3: A patient has a respiratory rate of 20. The nurse calculates this patient’s minute ventilation to
be:
1. 1 L/min
2. 2 L/min
3. 5 L/min
4. 10 L/min
Answer: 4
Rationale: The amount of ventilation is generally quantified by how much air the lungs move in one
minute, referred to as the minute ventilation. Minute ventilation is the product of respiratory rate and
depth (tidal volume - Vt). Normal (average) resting respiratory rate is about 12 breaths per minute.
Normal (average) resting depth tidal volume is about 500 mL in adults.
This yields a normal minute ventilation of 6 L/min: 12 breaths/min (bpm)  500 mL = 6,000 mL or 6 L.
So for this question the patient’s respiratory rate is 20 breaths per minute (bpm). The minute ventilation
would be 10 L/min. (20 bpm x 500mL = 10,000ml or 10L/min.)
Question 4:
The nurse, admitting a patient with diabetes, believes the patient is attempting to correct an acidotic
condition. Which of the following did this nurse most likely observe while assessing this patient?
1. Slow methodical respirations
2. Deep rapid respirations
3. Change in level of consciousness
4. Intact extraocular movements
Answer: 2
Rationale: In a state of metabolic acidosis, such as that which exists during diabetic ketoacidosis, the
medullary centers will stimulate the lungs to increase the minute ventilation to blow off CO2, even if
that level is normal. These rapid, deep respirations, referred to as Kussmaul’s respirations, are an
attempt to correct the arterial pH by decreasing respiratory acid. This process is referred to as
compensation.
Question 5:
The nurse is caring for a patient with metabolic acidosis. The nurse realizes that which of the following
laboratory values might be altered for this patient?
1. Ammonia
2. Blood-urea-nitrogen
3. Creatinine
4. Prothrombin
Answer: 1
Rationale: In the face of a high load of metabolic acids, the kidneys also increase their production
of the urinary buffer, ammonia. Under normal circumstances, ammonia excretion is about 30
mmol/day, or about 0.5 mmol/kg. This excretion can increase to about 280 mmol/day, but this
response takes several days to be completed. Answers 3 and 4 are not the best answers as these
can indicate renal failure but may not specifically indicate the ability of the kidney to produce
buffers. Answer 4 is indicative of anti-coagulation therapy like warfarin.
Question 6:
The nurse is reviewing a patient’s arterial blood gas results. Which of the following values should the
nurse study first?
1. PaCO2
2. HCO3
3. Compensation
4. pH
Answer: 4
Rationale: The steps to analyze an arterial blood gas results are as follows:
Step 1 - Assess the pH.
Step 2 - Assess the PaCO2.
Step 3 - Assess the bicarbonate HCO3.
Step 4 - Match the PaCo2 and the HCO3 to the pH. (To determine the primary problem)
Step 5 - Assess compensation. (To determine if the primary problem is being compensated)
Step 6 - Assess oxygenation.
NOTE** The book (Osborn) directs you in these steps:
Step 1—Assess the pH.
Step 2—Assess the PaCO2.
Step 3—Assess the bicarbonate and the base excess.
Step 4—Evaluate compensation.
This is just another way to interpret ABG’s, pH is always assessed first.
Question 7:
The nurse is caring for a patient with pneumonia who has arterial blood gas values of: pH 7.20, PaCO2 75,
HCO3- 26, PaO2 44. Which of the following would be a priority for this patient?
1. Assisting the patient to breathe into a paper bag.
2. Preparing to administer Sodium Bicarbonate IV.
3. Placement of the patient in high Fowler’s position.
4. Administration of the prn sedative available.
Answer: 3
Rationale: The patient is in respiratory acidosis. The main treatment for respiratory acidosis is correction of the
underlying disorder that led to its development. For a patient with pneumonia, this would include antibiotic therapy,
improving oxygenation, and management of fever. Placing the patient in high Fowler’s position will improve air
flow. Answers 1 and 4 are contraindicated because the patient is retaining PaCO2 in respiratory acidosis and
breathing into a paper bag will cause re-breathing of CO2 and will make the patient even more acidotic. And
administering a sedative will depress the rate of breathing and will also increase respiratory acidosis. Answer 2 is
only used when the use of sodium bicarbonate is indicated only for known bicarbonate-responsive acidosis, such as
that seen with renal failure and use of sodium bicarbonate is used to treat metabolic acidosis. So it is usually
avoided. (Sodium Bicarb may be seen to be used in CPR and during codes as last stitch efforts and is part of ACLS).
So answer 3 is the best answer and you also do not need an order to do this.
Question 8:
A patient is admitted in respiratory acidosis secondary to barbiturate overdose. Which of the following
will the nurse most likely assess in this patient?
1. Kussmaul’s respirations
2. Seizures
3. Slow, shallow respirations
4. Increased deep tendon reflexes
Answer: 3
Rationale: Whenever excretion of CO2 via the lungs fails to keep up with body's CO2 production,
respiratory acidosis will occur, such as with a drug overdose. Kussmaul respirations (rapid, deep breaths)
occur with metabolic acidosis, seizures are associated with respiratory alkalosis, and hyperreflexia is a
symptom of metabolic alkalosis.
Question 9:
The nurse is providing discharge instructions to a patient with respiratory alkalosis. Which of the
following statements indicates the patient understands the instructions?
1. “I will not take my Lasix without a potassium supplement.”
2. “I will not use Mylanta 5-6 times a day like I used to.”
3. “I will take a stress management class or seek counseling.”
4. “I will call my MD the next time I have diarrhea for a few days.”
Answer: 3
Rationale: Respiratory alkalosis is characterized by a lower than normal PaCO2 accompanied by an
elevated pH. Respiratory rate is a major determinate of the PaCO2 level. Excessively fast or deep
ventilation “blows off” the carbon dioxide, decreasing the level and increasing the pH causing alkalosis.
Psychological conditions such as anxiety and panic or severe pain can also cause overventilation. Patients
with psychological hyperventilation syndromes should benefit from reassurance and methods to decrease
stress.
Answer 1, 2, 4 are related to metabolic conditions. Answer 1 particularly, is preventing hypokalemia and
not specific to respiratory acidosis.
Question 10:
A patient ABG’s come back as: pH: 7.33; PaCo2: 60; HCO3: 34, PaO2: 88; SaO2: 90%.
1.
2.
3.
4.
Uncompensated Respiratory Acidosis with hypoxemia.
Partially-compensated respiratory alkalosis with normal oxygenation.
Partially-compensated respiratory acidosis with hypoxemia.
Respiratory acidosis with full compensation and with hypoxemia.
Answer is 3.
pH is low – acidotic
PaCO2 is high – acidotic
HCO3 is high – alkalotic
PaO2 and SaO2 are low – hypoxemia
The primary problem is acidosis (pH) the system that matches pH (acidosis) is the respiratory system
(PaCO2) so it’s respiratory. The HCO3 is alkalotic and trying to correct the acidosis so there is
compensation present. The pH is still not in normal range so it is partial in compensation. The PaO2 and
SaO2 indicate abnormal oxygenation so hypoxemia is present.
Therefore the full interpretation is – Partially-compensated respiratory acidosis with hypoxemia.
Question 11:
Interpret the following ABG’s: pH: 7.48; PaCO2: 42; HCO3: 30; PaO2: 94; SaO2:100%.
1.
2.
3.
4.
Metabolic acidosis without compensation.
Respiratory alkalosis with partial compensation.
Respiratory alkalosis without compensation.
Metabolic alkalosis without compensation.
Answer is 4.
pH is high – alkalotic
PaCO2 is normal
HCO3 is high – alkalotic
PaO2 and SaO2 are normal – normal oxygenation
The primary problem is alkalosis (pH) the system that matches pH (alkalosis) is the Renal system
(HCO3) so it’s metabolic. The respiratory system (PaCO2) is normal and NOT moving to correct the
alkalosis so there is NO compensation present. The PaO2 and SaO2 indicate normal oxygenation so no
hypoxemia is present.
Therefore the full interpretation is – metabolic alkalosis without compensation.
Question 12:
In question 11, what is the oxygenation status?
1. Normal oxygenation
2. Hypoxemia
Answer is 1.
The PaO2 and SaO2 are within the normal ranges, so therefore there is adequate oxygenation.
Question 13:
Interpret the following ABG’s: pH: 7.38; PaCO2: 38; HCO3: 24; PaO2: 96; SaO2:98%.
1.
2.
3.
4.
Respiratory Alkalosis
Normal ABG’s
Metabolic Alkalosis
None of the
Answer is 2.
pH is normal
PaCO2 is normal
HCO3 is normal
PaO2 and SaO2 are normal.
Since all the results are in normal range the ABG is normal.
Question 14:
Interpret the following ABG’s: pH: 7.21; PaCO2: 60; HCO3: 24; PaO2: 66; SaO2:88%.
1.
2.
3.
4.
Normal ABG’s
Uncompensated Respiratory Acidosis with hypoxemia.
Partially-Compensated Metabolic Acidosis with hypoxemia.
Fully-compensated Respiratory Acidosis and normal oxygenation.
Answer is 2.
pH is low – acidotic
PaCO2 is high – acidotic
HCO3 is normal
PaO2 and SaO2 are low – hypoxemia
The primary problem is acidosis (pH) the system that matches pH (acidosis) is the PaCO2 so it’s
respiratory. The HCO3 is normal and NOT moving to correct the acidosis so there is NO compensation
present. The PaO2 and SaO2 are low and indicate abnormal oxygenation so hypoxemia is present.
Therefore the full interpretation is – Uncompensated respiratory acidosis with hypoxemia
Question 15:
Interpret the following ABG results: pH: 7.42; PaCO2: 58; HCO3: 31.
1.
2.
3.
4.
Partially-compensated metabolic acidosis.
Fully compensated metabolic alkalosis.
Uncompensated metabolic alkalosis.
Fully compensated respiratory acidosis.
Answer is 2.
pH is normal but on the higher side of the normal range (>7.40 but <7.45).
PaCO2 is high - acidotic
HCO3 is high – alkalotic
The (pH) is normal but it is greater than 7.40, so the original disorder was probably alkalosis, the system
that would match pH is the renal system (HCO3), because it is alkalotic. So the original problem was
metabolic alkalosis. The respiratory system (PaCO2) is acidotic and moved to correct the alkalosis. So
full compensation is present. (pH is back in normal range).
Therefore the full interpretation is – Fully compensated metabolic alkalosis.
Question 16:
Interpret the following ABG results: pH: 7.36; PaCO2: 29; HCO3: 19.
1.
2.
3.
4.
Fully compensated respiratory acidosis
Fully compensated respiratory alkalosis
Fully compensated metabolic acidosis
Fully compensated metabolic alkalosis
Answer is 3.
pH is normal but on the lower side of the normal range (<7.40 but >7.35).
PaCO2 is low - alkalotic
HCO3 is low - acidotic
The (pH) is normal but it is less than 7.40, so the original disorder was probably acidosis, the system that
would match pH is the renal system (HCO3), because it is acidotic. So the original problem was
metabolic acidosis. The respiratory system (PaCO2) is alkalotic and moved to correct the acidosis. So full
compensation is present. (pH is back in normal range).
Therefore the full interpretation is – Fully compensated metabolic acidosis.