Acid-Base & ABGs — Set 1

1

A nurse reviews an arterial blood gas for a client admitted with an acute COPD exacerbation: pH 7.30, PaCO₂ 58 mmHg, HCO₃⁻ 25 mEq/L. How should the nurse interpret this result?

Correct: A

The pH is acidic (below 7.35) and the PaCO₂ is elevated (above 45 mmHg) in the same acidic direction, so the lungs are the cause: respiratory acidosis. The HCO₃⁻ is still within the normal 22–26 mEq/L range, which means the kidneys have not yet begun to compensate — making it uncompensated. Full compensation would show a clearly elevated bicarbonate pulling the pH back toward normal, which hasn't happened here.

A. Correct. Acidic pH + high CO₂ (same direction) = respiratory acidosis; a normal bicarbonate means no compensation yet.
B. Fully compensated would require a normal pH (7.35–7.45) with an elevated bicarbonate — the pH here is still 7.30.
C. Respiratory alkalosis would show an alkalotic pH (above 7.45) with a low CO₂ — the opposite of these values.
D. Metabolic acidosis would show a low bicarbonate (below 22); this bicarbonate is normal, and the CO₂ is the abnormal value.

2

A client with diabetic ketoacidosis has these values: pH 7.22, PaCO₂ 28 mmHg, HCO₃⁻ 12 mEq/L. Which interpretation is correct?

Correct: D

The pH is acidic and the HCO₃⁻ is low (below 22) in the same acidic direction, so the primary problem is metabolic acidosis — expected in DKA from ketoacid accumulation. The PaCO₂ is low (below 35), which is the lungs blowing off CO₂ (Kussmaul respirations) to raise the pH: respiratory compensation. Because the pH is still abnormal, compensation is partial, not complete.

A. Metabolic alkalosis needs an alkalotic pH and high bicarbonate — the opposite of these values.
B. A mixed acidosis would require the CO₂ to be high (adding acid); here the low CO₂ is helping, not a second acidosis.
C. Respiratory acidosis would show a HIGH CO₂; here the CO₂ is low.
D. Correct. Low pH + low bicarbonate = metabolic acidosis; the low CO₂ is compensatory.

3

A client is admitted with persistent vomiting for three days. Which acid-base disturbance should the nurse most anticipate?

Correct: A

Prolonged vomiting removes hydrochloric acid from the stomach. Losing acid (hydrogen ions) leaves the blood relatively more basic, and the kidneys retain bicarbonate as chloride and volume drop — producing a metabolic alkalosis. Expect a high pH and a high HCO₃⁻, often with hypokalemia and hypochloremia.

A. Correct. Loss of gastric acid raises pH → metabolic alkalosis.
B. Respiratory acidosis is driven by hypoventilation and CO₂ retention.
C. Respiratory alkalosis is driven by hyperventilation, not GI acid loss.
D. Metabolic acidosis comes from gaining acid or losing bicarbonate (e.g., diarrhea, DKA), not vomiting.

4

Which arterial blood gas value is the primary determinant of the respiratory component of acid-base balance?

Correct: C

PaCO₂ reflects how much carbon dioxide the lungs are retaining or blowing off, so it is the respiratory component. HCO₃⁻ is controlled by the kidneys and is the metabolic component. pH is the overall net result, and PaO₂ reflects oxygenation, not acid-base status.

A. Bicarbonate is the metabolic (kidney) component.
B. pH is the overall verdict, not specifically respiratory.
C. Correct. CO₂ is regulated by ventilation — the respiratory side.
D. PaO₂ measures oxygenation and is interpreted separately from acid-base.

5

A client has: pH 7.37, PaCO₂ 60 mmHg, HCO₃⁻ 34 mEq/L. How should the nurse interpret this gas?

Correct: A

The pH is within the normal range (7.35–7.45) but BOTH the CO₂ and the bicarbonate are abnormal, which signals full compensation. To find the primary problem, split the normal range at 7.40: a pH of 7.37 sits on the acidic side, and the high CO₂ is the acidic driver — so this is a fully compensated respiratory acidosis (classic chronic CO₂ retainer whose kidneys have caught up).

A. Correct. Normal pH on the acidic side of 7.40 + high CO₂ = compensated respiratory acidosis.
B. Uncompensated would show a normal bicarbonate and an abnormal pH — here both are abnormal and pH is normal.
C. A mixed disorder would push the pH further off, not return it to normal.
D. The primary problem is acidic (pH 7.37 < 7.40) with CO₂ the driver, so respiratory, not metabolic alkalosis.

6

An anxious client is hyperventilating in the emergency department. Which ABG pattern should the nurse expect if no compensation has occurred yet?

Correct: D

Hyperventilation blows off CO₂. Losing that acid raises the pH (alkalosis) and lowers the PaCO₂ — a respiratory alkalosis. With no compensation yet, the kidneys have not had time to dump bicarbonate, so HCO₃⁻ stays normal.

A. That pattern (low pH, high CO₂) is respiratory acidosis — the opposite problem.
B. A high bicarbonate would indicate metabolic alkalosis, not acute hyperventilation.
C. Low bicarbonate with low CO₂ suggests a compensated metabolic acidosis, not hyperventilation.
D. Correct. Blowing off CO₂ → high pH + low CO₂; normal bicarbonate = uncompensated.

7

A client's ABG shows a high-anion-gap metabolic acidosis. Which finding in the client's history best explains this result?

Correct: D

A high anion gap means unmeasured acid has been ADDED to the blood. Lactic acid from shock/sepsis is a classic cause (remember MUDPILES). Diarrhea causes a normal-gap acidosis from bicarbonate loss, while NG suction and loop diuretics cause a metabolic ALKALOSIS, not acidosis.

A. Diarrhea loses bicarbonate → NORMAL-gap (hyperchloremic) acidosis, not high gap.
B. NG suction removes acid → metabolic alkalosis.
C. Loop diuretics cause a contraction metabolic alkalosis.
D. Correct. Added lactic acid widens the anion gap.

8

What is the normal reference range for arterial pH?

Correct: D

Normal arterial pH is 7.35 to 7.45. Below 7.35 is acidemia; above 7.45 is alkalemia. Committing this range to memory is the first step of every ABG interpretation.

A. 7.25–7.35 is entirely within the acidemic range.
B. 7.00–7.35 spans severe acidemia up to the low-normal border.
C. 7.45–7.55 is entirely within the alkalemic range.
D. Correct. 7.35–7.45 is the normal arterial pH range.

9

A client with an opioid overdose is difficult to arouse with a slow respiratory rate. Which acid-base disturbance is the priority concern?

Correct: B

Opioids depress the respiratory drive, causing hypoventilation. The client retains CO₂, which combines with water to form carbonic acid and drops the pH — a respiratory acidosis. The priority is supporting ventilation and oxygenation (and reversing the opioid); the retained CO₂ is what the ABG will show.

A. Metabolic alkalosis is unrelated to opioid-induced respiratory depression.
B. Correct. Hypoventilation retains CO₂ → respiratory acidosis.
C. Metabolic acidosis is a kidney/metabolism problem, not the primary issue in acute hypoventilation.
D. Respiratory alkalosis comes from hyperventilation, the opposite of opioid effect.

10

A client has: pH 7.31, PaCO₂ 34 mmHg, HCO₃⁻ 16 mEq/L, Na⁺ 140, Cl⁻ 100. What is the anion gap, and what does it indicate?

Correct: B

Anion gap = Na⁺ − (Cl⁻ + HCO₃⁻) = 140 − (100 + 16) = 24 mEq/L. Normal is about 8–12, so 24 is elevated — a high-anion-gap metabolic acidosis, meaning unmeasured acid (lactate, ketones, toxins) has been added. The low pH and low bicarbonate confirm the metabolic acidosis; the gap tells you the cause category.

A. The anion gap does not diagnose respiratory disorders, and 40 is not the computed value.
B. Correct. 140 − (100 + 16) = 24, well above the normal 8–12.
C. 16 is not the computed gap, and that value would still be borderline-high, not normal.
D. 8 would be a miscalculation; recheck 140 − 116.