Examkin

Question

Difficulty: HardInterpreting Laboratory Results

A hospitalist is evaluating the arterial blood gas (ABG) and metabolic panel profiles for several adult patients upon admission. Match each laboratory profile to its most likely clinical etiology. Assume a normal serum anion gap is 88-1212 mEq/L.

  • pH 7.257.25, pCO2pCO_2 6060 mmHg, HCO3−HCO_3^- 2626 mEq/L. Serum Na+Na^+ 140140 mEq/L, Cl−Cl^- 105105 mEq/L.Acute opiate toxicity
  • pH 7.287.28, pCO2pCO_2 2828 mmHg, HCO3−HCO_3^- 1212 mEq/L. Serum Na+Na^+ 140140 mEq/L, Cl−Cl^- 100100 mEq/L.Diabetic ketoacidosis
  • pH 7.307.30, pCO2pCO_2 3030 mmHg, HCO3−HCO_3^- 1414 mEq/L. Serum Na+Na^+ 140140 mEq/L, Cl−Cl^- 114114 mEq/L.Profound secretory diarrhea
  • pH 7.507.50, pCO2pCO_2 4545 mmHg, HCO3−HCO_3^- 3434 mEq/L. Urine Cl−Cl^- 1010 mEq/L.Surreptitious self-induced emesis
  • pH 7.557.55, pCO2pCO_2 4848 mmHg, HCO3−HCO_3^- 4040 mEq/L. Urine Cl−Cl^- 5555 mEq/L.Primary hyperaldosteronism

Answer

Laboratory profiles must be systematically evaluated by identifying the primary disturbance (pH, pCO2, HCO3-), calculating the anion gap for metabolic acidosis, and assessing urine chloride for metabolic alkalosis to find the correct etiology.
Each laboratory profile uniquely matches a clinical etiology through systematic evaluation of pH, pCO2, bicarbonate, anion gap, and urine chloride. Acute respiratory acidosis matches opiate toxicity; high anion gap metabolic acidosis matches diabetic ketoacidosis; normal anion gap metabolic acidosis matches secretory diarrhea; saline-responsive metabolic alkalosis matches emesis; and saline-resistant metabolic alkalosis matches primary hyperaldosteronism.

Step-by-Step Solution

1
Determine the primary acid-base disturbance.
Identify whether the primary process is an acidosis (pH < 7.35) or alkalosis (pH > 7.45), and whether it is metabolically (HCO3-) or respiratorily (pCO2) driven.
This categorizes the disorder into one of four primary buckets: metabolic acidosis, metabolic alkalosis, respiratory acidosis, or respiratory alkalosis.
2
Calculate the serum anion gap for cases of metabolic acidosis.
Using the formula Anion Gap = Na+ - (Cl- + HCO3-), determine if the gap is normal (8-12 mEq/L) or elevated (>12 mEq/L).
A high anion gap indicates unmeasured organic acids (e.g., ketones in DKA), while a normal gap indicates direct bicarbonate loss (e.g., diarrhea).
3
Evaluate the urine chloride concentration for cases of metabolic alkalosis.
Classify the alkalosis as saline-responsive (Urine Cl- < 20 mEq/L) or saline-resistant (Urine Cl- > 20 mEq/L).
Low urine chloride signifies volume depletion and active renal chloride retention (e.g., vomiting), whereas high urine chloride indicates mineralocorticoid excess or profound potassium depletion (e.g., hyperaldosteronism).

Key Concept

Stepwise interpretation of acid-base disorders requires identifying the primary disturbance, calculating the anion gap for metabolic acidosis, and utilizing urine chloride levels to distinguish etiologies of metabolic alkalosis.
Rate this question

Topics

Interpreting Laboratory Results

More questions from this topic