Critical Care and ABG Interpretation Flashcards

A patient has ABG values: pH 7.28, PaCO2 55 mmHg, HCO3 24 mEq/L. This represents:

Answer: Respiratory acidosis (uncompensated)

pH below 7.35 (acidosis) with elevated PaCO2 and normal HCO3 indicates uncompensated acute respiratory acidosis.

A patient has ABG: pH 7.52, PaCO2 28 mmHg, HCO3 22 mEq/L. This is consistent with:

Answer: Respiratory alkalosis (uncompensated)

pH above 7.45 (alkalosis) with low PaCO2 and near-normal HCO3 indicates uncompensated acute respiratory alkalosis from hyperventilation.

Acute hypoxemic respiratory failure is defined by a PaO2/FiO2 (P/F) ratio below:

Answer: 300

A P/F ratio below 300 mmHg defines acute hypoxemic respiratory failure; values below 200 define ARDS and below 100 define severe ARDS (Berlin criteria).

In diabetic ketoacidosis (DKA), the respiratory compensation (Kussmaul respirations) produces:

Answer: Respiratory alkalosis to compensate for metabolic acidosis

Kussmaul respirations are deep, rapid breaths that blow off CO2, lowering PaCO2 to partially compensate for the metabolic acidosis of DKA.

The anion gap is calculated as:

Answer: Na+ – (Cl– + HCO3–)

The anion gap = Na+ – (Cl– + HCO3–); a normal anion gap is 8–12 mEq/L, and an elevated gap indicates unmeasured anions from conditions like lactic acidosis or DKA.

Which of the following causes a high anion gap metabolic acidosis?

Answer: Lactic acidosis

Lactic acidosis increases unmeasured anions (lactate), elevating the anion gap, unlike hyperchloremic (normal anion gap) acidoses such as diarrhea or RTA.