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Difficulty: MediumNephrology

Match each patient's laboratory profile with the most likely underlying clinical etiology.

  • ABG: pH 7.257.25, pCO 2_2 2424 mmHg, HCO 3−_3^- 1010 mEq/L. Serum: Na +^+ 140140 mEq/L, Cl −^- 105105 mEq/LUncontrolled type 1 diabetes mellitus
  • ABG: pH 7.527.52, pCO 2_2 4848 mmHg, HCO 3−_3^- 3838 mEq/L. Urine Cl −^- 88 mEq/LHyperemesis gravidarum
  • ABG: pH 7.287.28, pCO 2_2 6060 mmHg, HCO 3−_3^- 2626 mEq/LAcute heroin overdose
  • ABG: pH 7.317.31, pCO 2_2 3030 mmHg, HCO 3−_3^- 1515 mEq/L. Serum: Na +^+ 135135 mEq/L, Cl −^- 112112 mEq/LSevere infectious diarrhea
  • ABG: pH 7.447.44, pCO 2_2 2828 mmHg, HCO 3−_3^- 1919 mEq/LNormal third-trimester pregnancy

Answer

The correct matches require calculating the anion gap and assessing respiratory compensation chronicity to identify the primary acid-base disorder and its etiology.
Each laboratory profile represents a classic presentation of a primary acid-base disorder with appropriate physiologic compensation. Matching them accurately requires systematic calculation of the anion gap, expected compensation formulas, and an understanding of volume status via urine electrolytes.

Step-by-Step Solution

1
Calculate the anion gap (Na+−(Cl−+HCO3−)\text{Na}^+ - (\text{Cl}^- + \text{HCO}_3^-)) for the metabolic acidosis profiles (Profiles 1 and 4).
Profile 1 has an AG of 2525 mEq/L (HAGMA), while Profile 4 has an AG of 88 mEq/L (NAGMA).
Differentiating HAGMA from NAGMA isolates uncontrolled diabetes (HAGMA) from severe diarrhea (NAGMA).
2
Evaluate the metabolic alkalosis profile (Profile 2) using urine chloride.
Profile 2 shows a low urine chloride (88 mEq/L).
Low urine chloride (<20< 20 mEq/L) indicates a saline-responsive alkalosis, typically caused by upper gastrointestinal fluid loss such as hyperemesis gravidarum.
3
Analyze the ratio of change in pCO 2_2 to HCO 3−_3^- for the respiratory disorders (Profiles 3 and 5) to determine acuity.
Profile 3 shows an acute 11:1010 ratio of HCO 3−_3^- increase to pCO 2_2 increase. Profile 5 shows a chronic 44:1010 to 55:1010 ratio of HCO 3−_3^- decrease to pCO 2_2 decrease.
This distinguishes the acute hypoventilation of a heroin overdose from the chronic, progesterone-driven hyperventilation of a normal third-trimester pregnancy.

Key Concept

Interpretation of arterial blood gases and electrolyte panels to diagnose specific acid-base disorders
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Topics

Nephrology

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