Acute Cough Pathophysiology

Acute Cough Pathophysiology

• Cough is a normal physiological response protecting the respiratory tract.
• Receptors in head, neck, and chest stimulate nerve pathways to the cough centre.
• The afferent limb of the vagus nerve transmits information to the cough centre.
• Efferent pathways to airway and respiratory muscles result from the cough reflex.
• Cough duration classifies acute (<3 weeks), subacute (3-8 weeks), and chronic (>8 weeks).
• Acute cough accounts for over 50% of new patient visits to primary care.
• Viral infections in the upper respiratory tract frequently cause acute cough.
• Postinfectious cough, a subacute type, can persist after viral infection resolution.
• Postnasal drip (or Upper Airway Cough Syndrome) is another common cause.

Common Causes of Acute Cough

• Common Causes: Asthma, COPD, ACE inhibitor/NSAID use, environmental/occupational irritants, foreign bodies, GERD, heart failure, pulmonary embolism, rhinitis, sinusitis, Upper Airway Cough Syndrome, upper/lower respiratory tract infection (acute) & (post-infectious).
• Less Common Causes: Bronchiectasis, cystic fibrosis, interstitial lung disease, lung cancer, psychogenic cough, unexplained cough, Zenker diverticulum.

Goals of Therapy

• Diagnose and treat underlying cause.
• Relieve symptoms.
• Prevent complications.

Nonpharmacological Therapy

• Hydration and humidified air may be helpful, but evidence is limited.
• Nasal saline irrigation or nasal suctioning can help with nasal congestion.
• Avoid inhaling irritants like smoke, dust, pollutants, and allergens.

Pharmacologic Therapy

• Treating underlying conditions (e.g., GERD) is paramount.
• Specific treatments are not always possible (viral infections).
• Nonprescription antitussives and expectorants are often used.
• Evidence for efficacy of nonprescription cough medicines is limited, especially for children.
• Placebo effect is significant.

Antihistamines and Decongestants

• First-generation antihistamines may slightly reduce cough from URTIs.
• Second-generation antihistamines generally lack anticholinergic effects and often aren't effective for acute coughs.
• Decongestants, such as oxymetazoline, xylometazoline, pseudoephedrine, phenylephrine, may minimally help with postnasal drip.

Antitussives

• Act centrally within the brainstem to suppress cough mechanisms.
• Dextromethorphan and codeine may reduce cough counts in people with COPD, but evidence of effectiveness and risk of dependence/addiction associated with these substances is varied.
• Codeine and dextromethorphan are not recommended for URTI cough.

Expectorants

• Guaifenesin may enhance cough's effectiveness by promoting secretion clearance.
• Evidence for efficacy is limited.
• Adequate fluid intake and humidified air are considered complementary protussive or expectorant measures.

Other Agents

• Honey may be effective in suppressing cough, especially in children.
• Zinc lozenges can be used, although some studies question their efficacy.
• Local anesthetics like benzocaine, phenol, and menthol are sometimes used but lack sufficient evidence for widespread recommendations.
• NSAIDs have not shown efficacy in reducing cough severity.
• Ivy/thyme syrups may exhibit demonstrable, but modest cough reduction, but evidence supporting its tolerability is still insufficient.

Prescription Therapy

• Bronchodilators (e.g., Salbutamol, formoterol) may be useful in cases of obstructive lung diseases like asthma or COPD.
• Inhaled corticosteroids are sometimes used following respiratory infections, although more conclusive studies are needed to support this treatment strategy.

Cough in Special Populations (Children)

• Children experience URTI-associated acute cough 4 times more frequently than adults
• Health Canada restricts use of specific ingredients (cough suppressants, antihistamines) in children under 6 years of age.
• Codeine and hydrocodone should be avoided in children under 18 years of age.

Monitoring of Therapy

• Regularly assess patient symptom resolution and daily activities.