**Question:** Most common contributory factor to respiratory failure in patients with cystic fibrosis is:

A. Hypercapnia
B. Acidosis
C. Bronchiectasis
D. Mucus plugging

**Core Concept:** Cystic fibrosis (CF) is a genetic disorder affecting the respiratory and digestive systems, caused by mutations in the CFTR gene. The primary defect leads to thick, sticky mucus production, which obstructs airways and exacerbates infection and inflammation. This results in chronic respiratory complications, including bronchiectasis (irregular dilation and destruction of the bronchi) and impaired mucociliary clearance.

**Why the Correct Answer is Right:** The correct answer, D. Mucus plugging, is related to the primary defect in CF, which is the production of thick, sticky mucus. This mucus plugging obstructs the airways, leading to chronic bacterial colonization, inflammation, and subsequent lung damage. Over time, this promotes the development of bronchiectasis, which is another correct answer (C).

**Why Each Wrong Option is Incorrect:**

A. Hypercapnia (elevated carbon dioxide levels) and B. Acidosis (acid imbalance) are not directly caused by cystic fibrosis but rather by the respiratory complications associated with it, such as reduced lung function and impaired gas exchange.

C. While bronchiectasis is a complication of CF, it is not the most common cause of respiratory failure in patients with cystic fibrosis. Mucus plugging and subsequent bacterial colonization are the primary factors leading to respiratory failure in CF patients.

**Clinical Pearl:**

Patients with cystic fibrosis require close monitoring and early intervention for respiratory complications. Management involves pulmonary rehabilitation, antibiotics, mucolytics, and airway clearance techniques. Close follow-up with chest physicians is essential to detect lung deterioration and initiate appropriate therapy promptly.