Cystic Fibrosis (CF): Pathophysiology, Diagnosis, and Nursing Management

Cystic fibrosis is a life-limiting genetic disease affecting multiple organ systems, most notably the lungs and pancreas. This note reviews the genetics, pathophysiology, clinical presentation, diagnostic workup, and nursing management essentials that appear frequently on pediatric and med-surg exams.

Definition

• Cystic fibrosis (CF) is an autosomal recessive, multisystem disease characterized by altered function of the exocrine glands. It primarily affects the lungs, pancreas, and sweat glands.
• CF is caused by a mutation in the CFTR gene on chromosome 7, which regulates sodium and chloride channels in epithelial cells.
• The mutation produces abnormally thick, sticky mucus that plugs glands and organs, eventually leading to organ failure.

Genetics and Inheritance

• Inheritance pattern: Autosomal recessive
• Gene: CFTR on chromosome 7
• Carrier rate: ~1 in 25 Caucasians
• Two carrier parents: 25% chance child has CF; 50% chance child is a carrier
• One parent with CF + one carrier: 50% chance child has CF; 50% chance child is a carrier
• Carriers are asymptomatic and typically unaware they carry the gene.
• The most common mutation is ΔF508.
• Sweat chloride testing is the gold standard for diagnosis; values > 60 mmol/L are diagnostic.

Pathophysiology

• CFTR protein dysfunction alters salt and water movement across cell membranes, producing thickened mucus in the lungs, pancreas, and other organs.
• Respiratory: Thick mucus plugs the airways, causing chronic inflammation, recurrent infection, and bronchiectasis.
• Pancreatic: Mucus plugs the pancreatic duct, leading to atrophy and fibrotic cyst formation. Digestive enzymes cannot reach the intestine, causing malabsorption.
• Sweat glands: Produce sweat with high salt content — the classic "salty skin" finding.

Clinical Features — CF PANCREAS Mnemonic

• C — Chronic cough and wheeze: Hallmark respiratory symptoms from mucus obstruction.
• F — Failure to thrive: From malabsorption and increased metabolic demand.
• P — Pancreatic insufficiency: Inadequate digestive enzyme production.
• A — Alkalosis: From loss of hydrogen ions and electrolyte imbalance.
• N — Neonatal intestinal obstruction (meconium ileus): Often the first sign in newborns.
• C — Clubbing of fingers: Due to chronic hypoxemia in advanced lung disease.
• R — Rise in sweat chloride: Elevated > 60 mmol/L.
• E — Electrolyte imbalance (hypotonic dehydration): From excessive salt loss, especially in hot weather.

Other Clinical Manifestations

Respiratory

• Chronic productive cough
• Recurrent pneumonia (Pseudomonas, Staphylococcus)
• Nasal polyps, hemoptysis, pneumothorax

Gastrointestinal

• Distal intestinal obstruction syndrome (DIOS)
• Steatorrhea (fatty, greasy stools)
• Rectal prolapse

Metabolic

• Salty skin, hypotonic dehydration
• CF-related diabetes (requires insulin)
• Osteoporosis (vitamin D deficiency)

Reproductive

• Male infertility (absent vas deferens)
• Delayed puberty
• Reduced female fertility

Diagnosis

• Newborn screening is performed in all 50 states; positive screens require confirmatory testing.
• Sweat chloride test is the gold standard (> 60 mmol/L is diagnostic).
• Genetic testing identifies CFTR mutations; ΔF508 is most common.
• Chest X-ray may show bronchiectasis, hyperinflation, and segmental infiltrates.
• Stool analysis reveals steatorrhea in pancreatic insufficiency.

Respiratory Management

• Chest physiotherapy (CPT): Performed daily to mobilize secretions. Do before meals to prevent vomiting.
• Airway clearance techniques: Postural drainage, percussion, vibration, and high-frequency chest wall oscillation (vest therapy).
• Inhaled medications:
  • Bronchodilators (albuterol)
  • Mucolytics (dornase alfa / Pulmozyme)
  • Hypertonic saline
  • Inhaled antibiotics (TOBI)
• CFTR modulator therapy: Targets the underlying genetic defect. Examples: ivacaftor, lumacaftor/ivacaftor, elexacaftor/tezacaftor/ivacaftor.
• Antibiotics: For acute exacerbations and chronic suppression of Pseudomonas aeruginosa.
• Lung transplant: Option for advanced disease. Transplanted lungs do not carry the CF gene defect.

Nutritional Management

• High-calorie diet: ~150% of recommended daily intake
• High-protein diet: Essential for growth and tissue repair
• Pancreatic enzymes: Given with all meals and snacks
• Fat-soluble vitamin supplementation: A, D, E, and K
• Salt supplementation: Particularly in hot weather or with fever

Enzyme administration pearls:

• Give with all meals and snacks.
• Capsules may be opened and sprinkled on acidic foods such as applesauce.
• Never mix with milk or hot foods/water — this destroys the enzymes.
• CF-related diabetes requires insulin therapy.

Nursing Interventions

• Assess respiratory status frequently: cough, sputum, wheezing, work of breathing.
• Administer CPT before meals; perform airway clearance as ordered.
• Give pancreatic enzymes with all meals and snacks; teach proper technique.
• Monitor growth and nutritional status; weigh child at every visit.
• Monitor for complications: CF-related diabetes, liver disease, osteoporosis.
• Provide genetic counseling: review autosomal recessive inheritance and recurrence risks.
• Educate on medication adherence — nonadherence is common in adolescents.
• Promote physical activity to improve lung function and overall health.

Exam Traps

• Do NOT perform CPT after meals — it increases vomiting risk. Perform before meals.
• Do NOT mix pancreatic enzymes with milk or hot water — this destroys them. Use acidic foods like applesauce.
• Do NOT use antibiotics for viral infections — antibiotics target bacterial infections like Pseudomonas.
• Do NOT assume a child on enzymes has adequate nutrition — monitor growth and stool patterns.
• Do NOT forget CF is autosomal recessive — both parents must be carriers.
• Do NOT forget the CF PANCREAS mnemonic.

Key Takeaways

• CF is an autosomal recessive disorder of the CFTR gene on chromosome 7; ΔF508 is the most common mutation.
• Sweat chloride > 60 mmol/L confirms diagnosis.
• Meconium ileus in a newborn is a classic first sign of CF.
• Perform CPT before meals, and give pancreatic enzymes with every meal and snack (never with milk or hot foods).
• Pseudomonas aeruginosa is a common and serious respiratory pathogen in CF.
• CFTR modulators (e.g., elexacaftor/tezacaftor/ivacaftor) target the underlying genetic defect and have transformed CF care.