Bedside tests
Sputum examination
- Collect a good sample and send it for microscopy (Gram stain and auramine/ZN stain), culture and cytology
- Clear and colourless (chronic bronchitis)
- Yellow-green (pulmonary infection)
- Red (haemoptysis)
- Black (smoke, coal dust)
- Frothy white-pink (pulmonary oedema)
Peak expiratory flow (PEF)
- Maximal forced expiration through a peak flow meter
- Correlates well with FEV1 as an estimate of airway calibre but is more effort-dependent
Pulse oximetry
- Non-invasive assessment of peripheral O2 saturation
- Worry if less than or equals to 80%, unless it is normal in that patient (e.g. COPD)
- Check ABG
- Erroneous readings: poor perfusion, motion, excess light, skin pigmentation, nail varnish, dyshaemoglobinemia and carbon monoxide poisoning
Arterial blood gas (ABG) analysis
- Heparinised blood taken from the radial branch or femoral artery
- pH, PaO2 and PaCO3 are measured using an automatic analyser
- pH normal 7.35 to 7.45
- PaO2 normal 10.5 to 13.5kPa
- PaCO2 normal 4.5 to 6.0 kPa
- Type 1 respiratory failure (respiratory compensation
- Type 2 respiratory failure (no respiratory compensation)
Alveolar-arterial O2 concentration gradient
- Normal range 0.2 - 1.5kPa aged 25 years and 1.5 - 3.0 kPa aged 75 years
- High - problem with O2 transfer
- Low - hypoventilation
Spirometry
- Measures lung volumes
- FEV1 and FVC
- Objective defect (e.g. asthma, COPD)
- FEV1/FVC ratio is <75%
- Restrictive defect (e.g. pulmonary fibrosis, sarcoidosis, pleural effusion, connective tissue diseases, neuromuscular problems, interstitial pneumonias, obesity)
- FEV1/FVC ratio is 75% and above
Further investigations
Lung function tests
Radiology
Fibreoptic bronchoscopy
Bronchoalveolar lavage
Lung biopsy
Surgical procedures
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