Cough is a protective reflex that clears irritants from the airways. It can be triggered by infections, inhaled particles, acid reflux, or inflammation. The cough reflex arc involves receptors in the airways, vagus nerve, cough center in the medulla, and motor nerves. Coughs are classified by duration as acute (<3 weeks), subacute (3-8 weeks), or chronic (>8 weeks). Common causes include respiratory infections, post-infectious cough, asthma, GERD, smoking, and lung diseases. Evaluation involves assessing for life-threatening conditions like PE, heart failure, or lung cancer indicated by red flags like fever, weight loss, or hemoptysis.

1. Cough
Dr. Natnael Habtamu

2. Introduction
• Definition: A cough is a protective mechanism that forcefully expels
air from the lungs to clear secretions, foreign bodies, and irritants
from the airway, and can be triggered by various conditions

3. Pathophysiology
• Triggers: cough may be voluntary or a reflex to airway
irritants/triggers
• Mechanical (When Mucociliary Clearance is Overloaded or Weakened)
• Inhaled/aspirated solid or particulate matter (e.g., smoke, dust)
• Mucus
• Chemical
• Gastric acid (GERD)
• Inflammatory mediators: bradykinin, prostaglandin E2
• Thermal: cold air

4. Pathophysiology
• Cough reflex arc
• Triggers irritation of cough receptors in the nose, sinuses, upper and lower
respiratory tract
• Transmission along the afferent pathway via the internal laryngeal nerve of the vagus
nerve (CN X) to the cough center in the medulla
• Generation of efferent signal in the medulla and initiation of cough via the vagus,
phrenic, and spinal motor nerves
• Mechanism of cough reflex: initiation of the cough reflex arc leads to
• Rapid inspiration, closure of the epiglottis and vocal cords (which traps inhaled air in
the lungs), and contraction of the diaphragm, expiratory, and abdominal muscles →
rapid increase of intrathoracic pressure
• A sudden opening of the vocal cords and forceful expulsion of air from the lungs

5. Classification: By duration
• Adults and adolescents > 14 years of age
• Acute cough: < 3 weeks
• Subacute cough: 3–8 weeks
• Chronic cough: > 8 weeks
• Children and adolescents ≤ 14 years of age
• Acute cough: < 2 weeks
• Subacute cough: 2–4 weeks
• Chronic cough: at least daily cough for > 4 weeks

6. Etiology
Adults [7][13][14] Children
Acute cough
•Respiratory tract infections (most common)
• URTIs, e.g., common cold, influenza
• LRTIs, e.g., acute bronchitis, pneumonia, pertussis
•Exacerbation of chronic conditions, e.g.:
• UACS
• Acute exacerbation of bronchiectasis
• Asthma exacerbation
• AECOPD
•Acute heart failure
•Pulmonary embolism
•Acute inhalation injury
•Respiratory tract infections (most common)
• URTIs, e.g., common cold, influenza
• LRTIs, e.g., acute bronchitis, pneumonia, pertussis, bronchiolitis
• Croup
•Initial presentation or exacerbation of a chronic condition, e.g.:
• Asthma
• Cystic fibrosis
•Foreign body aspiration
Subacute cough
•Postinfectious cough (most common)
•Pneumonia
•Pertussis
•New onset or exacerbation of a chronic condition, e.g.:
• UACS
• Asthma
• GERD
• COPD
• NAEB
• Bronchiectasis
•Tuberculosis
•Chronic foreign body airway obstruction (especially in young children)
Chronic cough
•Common
• UACS
• Asthma
• GERD
• NAEB
• Drug-induced cough, e.g., caused by ACE
inhibitors, sitagliptin [13]
• Irritation, e.g., due to environmental triggers, tobacco use
•Less common
• COPD
• Bronchiectasis
• Pulmonary tuberculosis
• Interstitial lung disease (e.g., sarcoidosis, silicosis)
• Chronic hypersensitivity pneumonitis
• Lung cancer
• Obstructive sleep apnea
•Older children
• Asthma
• Protracted bacterial bronchitis
• UACS
• Gastrointestinal conditions, e.g., GERD
• Immunodeficiency
• Atypical respiratory infection, e.g., mycoplasma pneumonia, pertussis
• New onset of a chronic condition, e.g., UACS, bronchiectasis, cystic
fibrosis, ciliary dyskinesia, interstitial lung disease
• Irritation, e.g., due to environmental triggers, tobacco smoke
• Tic cough [12]
• Somatic cough disorder [12]
•Infants
• Congenital defects
• Cardiac anomalies

7. Approach
• 1. Evaluate for and treat life-threatening causes of cough
• The following conditions should be considered in all adults who present with a cough
accompanied by signs of respiratory distress, hemodynamic instability, and/or red
flags for cough
• Severe asthma exacerbation or life-threatening asthma exacerbation
• Pneumonia with respiratory failure
• Severe acute exacerbation of chronic obstructive pulmonary disease (AECOPD)
• Pulmonary embolism (PE)
• Acute heart failure (AHF)
• Foreign body aspiration (FBA)
• Acute inhalation injury
• Pneumothorax
• Anaphylaxis
• Lung cancer

8. Approach
• 1. Evaluate for and treat life-threatening causes of cough
• Red flags for cough: These red flag features may indicate a life-threatening cause of
cough and typically warrant rapid evaluation and treatment.
• Smoking history, in particular:
• Current smokers > 45 years of age with a new or worsening cough and/or voice changes
• Patients 55–80 years old with ≥ 30 pack-years who either currently smoke or quit smoking ≤ 15
years ago
• Symptoms
• Fever
• Weight loss
• Severe dyspnea (especially at nighttime or when at rest)
• Weight gain with peripheral edema
• Dysphagia, hoarseness, vomiting
• Hemoptysis
• Recurrent pneumonia
• Excessive sputum production
• Abnormal physical examination and/or abnormal imaging findings