Pulmonary Investigations

Physical signs of respiratory disease:

Pulmonary investigations 1Pulmonary investigations 2Pulmonary investigations 3


CXR:

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A-a gradient:

  • To dx source of hypoxemia -> pulmonary or extra pulmonary
  • A-a gradient = (150 – 1.25 × PaCO2) – PaO2 {Normal Gradient Estimate = (Age/4) + 4}
  • Normal= 5-10 mmHg
  • Every decade -> ↑ by 1 mmHg

 

  • If ↑ = problem in the lungs
  1. V\Q mismatch: pneumonia, CHF, ARDS, atelectasis
  2. Shunts: PFO, ASD, PE, pulmonary AVM
  3. Alveolar hypoventilation: interstitial lung ds, PCP pneumonia

 

  • If -\↓ = problem outside the lungs
  1. Hypoventilation: COPD, CNS ds (opioids induced), neuromuscular ds
  2. Low FiO2: high altitudes

Spirometry:

Obstructive lung diseases:

  • FEV1 ↓↓
  • FVC ↓
  • FEV1\FVC ↓ (< 70%)
  • RV ↑↑ (air trapping)
  • TLC ↑
  • Reversible if the diff between pre
  • and post FEV1 > 200 ml AND >12%
    Or [PEFR >60 L\min or >15%]
  • Scoop out

Restrictive lung diseases:

  • FEV1 ↓
  • FVC ↓↓
  • FEV1\FVC normal or ↑
  • RV ↓
  • TLC ↓ (<80%)
  • Small lung volumes

Pulmonary investigations 6Pulmonary investigations 7Pulmonary investigations 9Pulmonary investigations 8


Pleural effusion fluid analysis:

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Download the PDF version: here


References:

  • Davidson’s Principles and Practice of Medicine
  • The Johns Hopkins Internal Medicine Board Review
  • Master the boards

 

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