What findings should I expect on lung auscultation in a patient with pneumonia?

Lung Auscultation Findings in Pneumonia

When auscultating the lungs of a patient with pneumonia, you should expect to hear inspiratory crackles (present in approximately 81% of cases), diminished breath sounds over the affected area, and possibly bronchial breathing, rhonchi, or expiratory crackles. 1, 2

Primary Auscultatory Findings

Crackles (Most Common Finding)

• Inspiratory crackles are the hallmark finding, detected in approximately 81% of pneumonia patients, representing the sudden opening of collapsed alveoli and airways filled with inflammatory exudate 1, 2
• These crackles are typically late inspiratory and have predominantly negative polarity (76% of inspiratory crackles) 3
• Expiratory crackles occur in approximately 65% of pneumonia patients, caused by sudden airway closure events, though they are less numerous than inspiratory crackles 3, 2
• Fine and coarse crackles together have 84.6% sensitivity for detecting ground-glass opacities and 88.9% sensitivity for consolidation 4

Diminished Breath Sounds

• Diminished or reduced breath sounds are a key finding in pneumonia, present in affected lung regions due to consolidation and reduced air movement 1
• The absence of runny nose combined with breathlessness, crackles, and diminished breath sounds significantly increases the likelihood of pneumonia 5, 1

Bronchial Breathing

• Bronchial breathing may be present over areas of consolidation, characterized by a higher ratio (R = 1.4) of inspiratory to expiratory spectral power in the 300-600 Hz frequency band compared to healthy lung (R = 0.5) 6
• This finding represents transmission of central airway sounds through consolidated lung tissue 6

Rhonchi

• Rhonchi are present in approximately 19% of pneumonia patients 2
• However, rhonchi alone do not significantly increase the likelihood of pneumonia on chest radiograph 1

Distribution Pattern of Findings

• Most cases have bilateral lesions (96.4%), though findings may be asymmetric 4
• Upper lung fields typically have normal breath sounds, while abnormal breath sounds increase in the basal fields where crackles are more commonly identified at the posterior chest 4
• Auscultation in lateral decubitus positions can elicit persistent late inspiratory crackles in the dependent lung in patients with pneumonia, a valuable diagnostic maneuver that reveals findings in 13 of 13 pneumonia patients who had normal upright auscultation 7

Clinical Decision Algorithm Based on Auscultatory Findings

High Probability of Pneumonia (Proceed to Chest Radiography)

• When crackles are present with fever ≥38°C, tachypnea, and dyspnea, pneumonia is highly likely 1
• The combination of absence of runny nose, breathlessness, crackles, diminished breath sounds, tachycardia (>100 bpm), and fever (≥37.8°C) yields an ROC curve area of 0.70 5

Intermediate Probability (Consider CRP Measurement)

• When crackles are present without fever or dyspnea, measure C-reactive protein (CRP) 1
• CRP >30 mg/L combined with clinical findings including crackles increases the ROC curve area to 0.77 and improves diagnostic classification by 28% 5, 1

Low Probability (Antibiotics Not Recommended)

• In patients with normal vital signs and normal overall lung examination despite isolated crackles, routine antibiotics are not recommended 1

Critical Pitfalls and Caveats

Crackles Are Not Specific to Bacterial Pneumonia

• Crackles occur in viral pneumonia, mycoplasma pneumonia, pulmonary edema, and interstitial lung diseases, and do not specifically indicate bacterial pneumonia 8
• In children, crackles and bronchial breathing demonstrated only 75% sensitivity and 57% specificity for radiographically confirmed pneumonia 8

Wheezing Suggests Non-Bacterial Etiology

• The presence of wheeze makes primary bacterial pneumonia very unlikely and suggests viral or mycoplasma infection instead 8
• Wheezing, cough, prolonged expirations, or rhonchi alone do not significantly increase the likelihood of pneumonia on chest radiograph 1

Age-Related Considerations

• Elderly patients may have atypical presentations with absent or altered physical examination findings despite radiographic pneumonia 1
• Advanced age (≥60 years) should lower the threshold for chest radiography even with normal auscultation 5

Transient Crackles in Healthy Individuals

• Transient late inspiratory crackles can occur in 18.9% of healthy control subjects when placed in lateral decubitus positions, but these clear quickly unlike the persistent crackles of pneumonia 7

Diagnostic Performance of Auscultation

• Tachypnea combined with abnormal breath sounds has a high negative predictive value (97%) for pneumonia, making the absence of these findings useful for ruling out pneumonia 1
• An acoustic pneumonia score based on automated quantification of crackles, rhonchi, and other adventitious sounds has a positive predictive value of 0.87-0.94 when the score exceeds 6 2
• Chest radiography should be performed in patients with suspected pneumonia who demonstrate abnormal vital signs and abnormal breath sounds 1