What is the difference between rhonchi, wheezes, and crackles in terms of diagnosis and management?

Distinguishing Rhonchi, Wheezes, and Crackles

Acoustic Characteristics

Rhonchi are low-pitched, continuous rumbling sounds with a dominant frequency of approximately 200 Hz or less, typically heard during forced expiration and often clearing with coughing. 1, 2

Wheezes

• High-pitched continuous sounds with a dominant frequency of 400 Hz or more, produced by oscillation of narrowed airway walls 3, 2
• Heard in both inspiration and expiration, though often more prominent during expiration 2
• Described as musical or whistling sounds that do not change significantly with coughing 3
• Produced by airway narrowing from edema, smooth muscle constriction, secretions, or mass lesions 3

Crackles (Rales)

• Discontinuous, explosive sounds rather than continuous like rhonchi or wheezes 4
• Typically heard during inspiration in conditions like bronchiolitis and pneumonia 4
• Result from sudden opening of previously closed small airways or movement of secretions 4

Clinical Significance and Disease Associations

Rhonchi

• Indicate airway secretions or obstruction but are not specific to any single disease 1
• Commonly found in COPD (especially during exacerbations), bronchiectasis, bronchitis, and pneumonia 4, 1
• May clear or change after coughing as secretions move, unlike wheezes 1
• Cannot predict severity of airflow obstruction—spirometry is mandatory 4, 5

Wheezes

• Most commonly associated with asthma but occur in any condition causing airway narrowing 3, 2
• Present in bronchiolitis (children 1-23 months), COPD exacerbations, and bronchospasm from any cause 4
• The proportion of respiratory cycle occupied by wheeze (tw/ttot) correlates with degree of obstruction, though too scattered to predict FEV1 reliably 2
• In children, recurrent wheeze is the most important symptom suggesting asthma 4

Crackles

• Characteristic of bronchiolitis in infants, presenting alongside tachypnea and increased work of breathing 4
• Found in pneumonia, pulmonary edema, and interstitial lung disease 4
• In COPD, crackles may indicate secretions but show no conclusive relationship to airway morphology or emphysema severity 6

Diagnostic Approach

Physical examination findings alone—including the presence of rhonchi, wheezes, or crackles—are insufficient for diagnosis and must be confirmed with objective testing. 4, 5

Essential Steps

1. Document the specific adventitious sound characteristics: pitch (high vs. low), timing (inspiratory vs. expiratory), continuity (continuous vs. discontinuous), and whether sounds clear with coughing 1, 2

2. Obtain spirometry in all patients with rhonchi or wheezes to confirm and quantify airflow obstruction, as physical signs cannot predict severity 4, 5

3. In children aged 5-16 years with wheeze, do not diagnose asthma based on symptoms alone—objective testing with spirometry showing reversible obstruction is required 4

4. In infants 1-23 months with tachypnea, wheeze, and crackles, diagnose bronchiolitis clinically without routine chest radiography or viral testing 4

Management Implications

For Rhonchi

• Initiate treatment based on spirometry results, not the presence or characteristics of rhonchi 5
• Mild COPD (FEV1 60-79% predicted): short-acting bronchodilators as needed 5
• Moderate COPD (FEV1 40-59% predicted): long-acting bronchodilators as cornerstone therapy 5
• Severe COPD (FEV1 <40% predicted): combination therapy with reassessment in 4-6 weeks 5

For Wheezes in Children

• Do not use asthma medications for isolated wheeze after bronchiolitis unless recurrent wheeze or dyspnea is present 4
• Children with chronic cough (>4 weeks) as the only symptom are unlikely to have asthma and require evaluation per chronic cough guidelines 4

For Crackles in Bronchiolitis

• Supportive care only—no bronchodilators, corticosteroids, or antibiotics unless bacterial superinfection is documented 4
• Monitor for increased work of breathing, apnea risk (especially in infants <12 weeks), and hydration status 4, 7

Critical Pitfalls to Avoid

• Never rely on adventitious sounds to gauge obstruction severity—always use spirometry 4, 5
• Do not use peak expiratory flow (PEF) for COPD assessment, as it may be only moderately reduced while FEV1 is severely affected 5
• Avoid diagnosing asthma in children based solely on wheeze—objective evidence of reversible obstruction is mandatory 4
• Do not prescribe inhaled osmotic agents or asthma medications for post-bronchiolitis cough unless true asthma is documented 4
• Recognize that automated wheeze detection shows large variability and cannot replace clinical spirometry 2