**Core Concept**
Alveolar hypoventilation leads to respiratory acidosis due to increased carbon dioxide retention, characterized by a low pH, elevated PaCO₂, and normal or reduced PaO₂. This condition arises when ventilation fails to match alveolar gas exchange, commonly in postoperative patients with suppressed respiratory drive.

**Why the Correct Answer is Right**
In the immediate postoperative period, especially after laparoscopic cholecystectomy with pneumoperitoneum, patients may experience reduced ventilation due to pain, sedation, or altered respiratory mechanics. This results in alveolar hypoventilation, causing CO₂ retention. The arterial blood gases show a pH of 7.29 (acidemia), PaCO₂ of 54 kPa (elevated), and PaO₂ of 60 kPa (mild hypoxemia), consistent with respiratory acidosis from hypoventilation. Unlike pulmonary embolism, which would present with hypoxemia and normal or low PaCO₂, and pulmonary edema, which typically has high pulmonary capillary pressure and bilateral rales, this profile fits best with hypoventilation.

**Why Each Wrong Option is Incorrect**
Option A: Acute pulmonary embolism causes hypoxemia and *low* PaCO₂ (not elevated), and is usually associated with tachycardia and sudden onset, not a pH of 7.29 with elevated CO₂.
Option B: CO₂ absorption from pneumoperitoneum is a theoretical risk but does not cause significant hypercapnia or acidosis in clinical practice; it is not a major contributor to gas exchange disturbance.
Option D: Pulmonary edema presents with bilateral crackles, hypoxemia, and often elevated pulmonary pressures; it would not typically show isolated hypercapnia without other signs like wheezing or chest X-ray findings.

**Clinical Pearl / High-Yield Fact**
Postoperative respiratory acidosis in the recovery room is most commonly due to alveolar hypoventilation, especially after abdominal surgery. Always assess ventilation status in hypotensive, tachycardic patients with respiratory acidosis—hypoventilation is the first-line differential before considering pulmonary pathology.

✓ Correct Answer: C. Alveolar hypoventilation