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Difficulty: MediumNephrology

Evaluate the provided arterial blood gas (ABG) and basic metabolic panel (BMP) profiles. Which clinical etiology most accurately corresponds to each laboratory pattern?

  • pH 7.257.25, PaCO2PaCO_2 6060 mm Hg, HCO3−HCO_3^- 2626 mEq/L, Na+Na^+ 140140 mEq/L, Cl−Cl^- 104104 mEq/LAcute opiate intoxication causing hypoventilation
  • pH 7.507.50, PaCO2PaCO_2 4848 mm Hg, HCO3−HCO_3^- 3636 mEq/L, Na+Na^+ 138138 mEq/L, Cl−Cl^- 9292 mEq/LIntractable emesis leading to volume and chloride depletion
  • pH 7.307.30, PaCO2PaCO_2 3030 mm Hg, HCO3−HCO_3^- 1414 mEq/L, Na+Na^+ 140140 mEq/L, Cl−Cl^- 114114 mEq/LExcessive gastrointestinal bicarbonate loss from an enterocutaneous fistula
  • pH 7.287.28, PaCO2PaCO_2 2828 mm Hg, HCO3−HCO_3^- 1212 mEq/L, Na+Na^+ 140140 mEq/L, Cl−Cl^- 102102 mEq/LAccumulation of serum ketoacids due to absolute insulin deficiency
  • pH 7.557.55, PaCO2PaCO_2 2222 mm Hg, HCO3−HCO_3^- 2020 mEq/L, Na+Na^+ 142142 mEq/L, Cl−Cl^- 108108 mEq/LHyperventilation secondary to an acute severe panic attack

Answer

Match each laboratory profile to its physiological driver by sequentially identifying the primary disturbance (via pH and PaCO2PaCO_2/HCO3−HCO_3^- direction) and calculating the anion gap for any metabolic acidosis.
By systematically interpreting the pH, PaCO2PaCO_2, and HCO3−HCO_3^-, along with calculating the anion gap for acidemic patients, the specific primary acid-base disturbance can be definitively identified and matched to its classic clinical trigger.

Step-by-Step Solution

1
Determine the primary acid-base disturbance for each profile using the pH.
Profiles 1, 3, and 4 exhibit acidemia (pH <7.35< 7.35). Profiles 2 and 5 exhibit alkalemia (pH >7.45> 7.45).
The net pH deviation dictates whether the primary underlying process is an acidosis or an alkalosis.
2
Differentiate respiratory versus metabolic drivers, and calculate the anion gap for metabolic acidoses.
Profile 1: Respiratory Acidosis. Profile 2: Metabolic Alkalosis. Profile 3: Normal Anion Gap Metabolic Acidosis (AG =12= 12). Profile 4: High Anion Gap Metabolic Acidosis (AG =26= 26). Profile 5: Respiratory Alkalosis.
Comparing PaCO2PaCO_2 and HCO3−HCO_3^- shifts against the pH identifies the driver. The anion gap formula (Na+−(Cl−+HCO3−)Na^+ - (Cl^- + HCO_3^-)) is mandatory to categorize metabolic acidosis.
3
Correlate the derived primary disorder with the appropriate clinical etiology.
Hypoventilation (opiate) correlates to Respiratory Acidosis. Vomiting correlates to Metabolic Alkalosis. Fistula output correlates to NAGMA. Ketoacidosis correlates to HAGMA. Hyperventilation (panic) correlates to Respiratory Alkalosis.
Specific clinical scenarios generate predictable, corresponding shifts in serum electrolytes and arterial blood gas values.

Key Concept

Identification and etiology of simple acid-base disorders based on laboratory parameters
Estimated Time:2m 0s
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Topics

Nephrology

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