Lung Sounds in Pneumonia
The most characteristic lung sounds in pneumonia are inspiratory crackles (also called rales), which are present in the majority of cases, along with diminished breath sounds in the affected areas. 1, 2
Primary Auscultatory Findings
Crackles (Rales) are the hallmark finding:
- Inspiratory crackles are heard in approximately 81% of pneumonia patients, representing the sudden opening of collapsed alveoli and airways filled with inflammatory exudate 1, 3
- These are typically coarse and mid-inspiratory in the early stages of pneumonia 4
- As pneumonia progresses, crackles shift to late-inspiratory timing and become finer 5, 4
- The crackle pitch progressively increases during inspiration (by approximately 80 Hz from early to late inspiration), reflecting recruitment of smaller airways 6
Diminished breath sounds are the second most important finding:
- Present in the affected lung regions due to consolidation and reduced air movement 1, 2
- The combination of breathlessness, crackles, and diminished breath sounds significantly increases pneumonia likelihood 1, 2
Additional Lung Sounds
Expiratory crackles occur in 65% of pneumonia patients (compared to only 9% in healthy controls) 3
Rhonchi (coarse, low-pitched sounds) are present in approximately 19% of pneumonia cases 3
Pleural friction rub may be heard when there is pleural involvement:
- Sounds like "creaking leather or walking on fresh snow" 7
- Biphasic (heard during both inspiration and expiration) 7
- Not cleared by coughing, unlike crackles 7
Clinical Decision-Making Algorithm
When crackles are present WITH:
- Fever ≥38°C
- Tachypnea
- Dyspnea
- Absence of runny nose
- → Pneumonia is highly likely; proceed to chest radiography 1, 2
When crackles are present WITHOUT fever or dyspnea:
- Consider measuring C-reactive protein (CRP)
- CRP >30 mg/L strengthens pneumonia diagnosis 1, 2
- CRP <10 mg/L makes pneumonia unlikely 1, 2
When lung sounds are completely normal:
- Pneumonia is unlikely (high negative predictive value of 97% when combined with normal vital signs) 2
- Routine antibiotics are not recommended 1, 2
Important Caveats
Wheezing alone does NOT suggest pneumonia and should not be used as a diagnostic criterion 2
Lung auscultation limitations include:
- Requires specialized training and quiet examination environment 1
- Particularly challenging in children with inconsistent breathing patterns 1
- WHO guidelines for frontline workers do not include auscultation in diagnostic criteria due to these limitations 1
Elderly patients may have atypical presentations with absent or altered physical examination findings despite radiographic pneumonia 1
Timing matters: The character of crackles changes during the clinical course, becoming finer and shifting to late inspiration as the patient improves 5, 4