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Difficulty: MediumNephrology

Match each clinical presentation of an acid-base disturbance to its most corresponding arterial blood gas (ABG) profile. Assume normal reference ranges for ABG are pH 7.35−7.457.35-7.45, PaCO2PaCO_2 35−4535-45 mm Hg, and HCO3−HCO_3^- 22−2622-26 mEq/L.

  • A 2121-year-old man with polyuria, polydipsia, abdominal pain, and rapid, deep respirations; laboratory evaluation reveals a serum glucose of 450450 mg/dL.pH 7.247.24, PaCO2PaCO_2 2424 mm Hg, HCO3−HCO_3^- 1010 mEq/L
  • A 4545-year-old man with intractable, severe vomiting for the past 33 days due to gastric outlet obstruction from a peptic ulcer.pH 7.517.51, PaCO2PaCO_2 4848 mm Hg, HCO3−HCO_3^- 3737 mEq/L
  • A 6868-year-old man with severe chronic obstructive pulmonary disease who is brought in lethargic after a 44-day history of worsening purulent sputum production.pH 7.297.29, PaCO2PaCO_2 6565 mm Hg, HCO3−HCO_3^- 3030 mEq/L
  • A 2222-year-old woman presenting with severe acute anxiety, dyspnea, and carpopedal spasms following a stressful life event.pH 7.587.58, PaCO2PaCO_2 2222 mm Hg, HCO3−HCO_3^- 2020 mEq/L

Answer

The clinical scenarios perfectly map to their primary acid-base derangements: DKA to metabolic acidosis (pH 7.247.24), vomiting to metabolic alkalosis (pH 7.517.51), COPD exacerbation to respiratory acidosis (pH 7.297.29), and hyperventilation from anxiety to respiratory alkalosis (pH 7.587.58).
Each clinical scenario corresponds to a classic acid-base disturbance. Diabetic ketoacidosis generates ketones, causing an anion gap metabolic acidosis. Severe vomiting causes loss of hydrogen and chloride ions, producing a hypochloremic metabolic alkalosis. COPD exacerbations lead to hypoventilation and CO2CO_2 retention (respiratory acidosis). Acute anxiety provokes hyperventilation, blowing off CO2CO_2 and resulting in respiratory alkalosis. Matching the primary directional change in pH, PaCO2PaCO_2, and HCO3−HCO_3^- while verifying expected compensation formulas confirms the correct associations.

Step-by-Step Solution

1
Identify the primary acid-base disturbance based on the clinical history.
DKA causes metabolic acidosis; vomiting causes metabolic alkalosis; COPD exacerbation causes respiratory acidosis; severe anxiety/hyperventilation causes respiratory alkalosis.
Determines the expected directional changes in pH, PaCO2PaCO_2, and HCO3−HCO_3^- before looking at the specific numeric options.
2
Analyze the ABG profiles to find the primary disorder by matching pH with the corresponding primary derangement.
pH 7.247.24 with low HCO3−HCO_3^- is metabolic acidosis. pH 7.517.51 with high HCO3−HCO_3^- is metabolic alkalosis. pH 7.297.29 with high PaCO2PaCO_2 is respiratory acidosis. pH 7.587.58 with low PaCO2PaCO_2 is respiratory alkalosis.
Links the clinical condition directly to the correct ABG pattern.
3
Verify appropriate physiological compensation for each disorder using standard formulas.
Winter's formula for the DKA ABG yields an expected PaCO2PaCO_2 of 23±223 \pm 2 mm Hg. Alkalosis compensation yields a PaCO2PaCO_2 around 4848 mm Hg. Acute respiratory alkalosis drops HCO3−HCO_3^- to exactly 2020 mEq/L.
Confirms the exact ABG profile matches the pure nature of the disorder and validates the initial matching.

Key Concept

Diagnosis of acid-base disorders requires correlating the clinical history with arterial blood gas primary derangements (metabolic vs. respiratory) and calculating expected physiological compensations.

Alternative Method

Instead of executing full compensation calculations for every option, simply identifying the primary disturbance (e.g., pH < 7.357.35 and low HCO3−HCO_3^- strictly defines a metabolic acidosis) is often sufficient to uniquely map each clinical scenario to its corresponding ABG profile in a single-best-match format.
Estimated Time:2m 0s
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Nephrology

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