What sounds are heard on lung auscultation in Acute Pulmonary Oedema (APO)?

Lung Auscultation Findings in Acute Pulmonary Edema (APO)

In acute pulmonary edema, bilateral fine crackles (rales) are the predominant auscultatory finding, typically beginning at the lung bases and progressing upward as pulmonary congestion worsens.

Characteristic Auscultatory Findings in APO

• Fine crackles (rales): High-pitched, short, explosive sounds heard during late inspiration, resembling the sound of hair being rubbed between fingers or Velcro being pulled apart 1
• Distribution pattern: Typically begins at the lung bases (bi-basal) and progresses upward as pulmonary congestion worsens 1, 2
• Timing: Predominantly heard during the inspiratory phase, especially late inspiration 1
• Progression: As APO worsens, crackles extend from basilar regions to more widespread distribution throughout the lung fields 1

Clinical Significance of Auscultatory Findings

• The presence of fine crackles is a key physical finding in left heart failure and indicates pulmonary congestion/edema 1, 2
• Inspiratory lung crackles represent the equalization of distal airway pressures caused by the abrupt opening of collapsed alveoli and adjacent airways 3
• The severity of crackles often correlates with disease progression, with more extensive crackles suggesting more severe pulmonary congestion 1
• The likelihood of radiographic confirmation of pulmonary edema increases in the presence of crackles on auscultation 3

Additional Auscultatory Findings That May Be Present

• Wheezing: May be present due to bronchospasm or compression of small airways by edema fluid 4
• Decreased breath sounds: In severe cases, areas of the lung may have diminished breath sounds due to significant fluid accumulation 2
• S3 gallop: Often accompanies the pulmonary findings as a sign of ventricular failure 2

Limitations and Pitfalls of Lung Auscultation in APO

• The absence of crackles does not rule out significant pulmonary congestion, as pronounced pulmonary edema can be present without auscultatory signs 1, 2
• Traditional acoustic stethoscopes have limitations in achieving reliable, reproducible interpretations of lung sounds, especially in noisy environments 3
• Lung auscultation requires specialized training to differentiate sounds correctly 3
• Auscultatory findings may have poor correlation with the actual severity of lung congestion when compared to more objective measures like lung ultrasound (shared variance of only 12%) 5

Differential Diagnostic Considerations

• Similar crackles may be heard in pneumonia, interstitial lung diseases, and pulmonary fibrosis 1
• In pulmonary veno-occlusive disease (PVOD), bi-basal crackles are considered an unusual finding compared to other forms of pulmonary arterial hypertension 3
• Digital clubbing with bi-basal crackles should raise suspicion for PVOD rather than simple APO 3

Complementary Diagnostic Approaches

• Lung ultrasound has superior diagnostic accuracy (sensitivity 94%, specificity 92%) compared to auscultation for detecting pulmonary edema 2
• Chest radiography showing peri-bronchial cuffing, cardiomegaly, pulmonary venous congestion, and pleural effusion supports the diagnosis 3, 2
• Natriuretic peptide levels (BNP or NT-proBNP) should be obtained to support the clinical diagnosis 3, 2