Bedside Pulmonary Function Tests - Full Details (MD Exam 10 Marks Answer)

Definition and Introduction

Classification of Bedside PFTs

1. Snider's Match Blowing Test
2. Forced Expiratory Time (FET)
3. Seberese's Single Breath Count
4. Seberese's Breath Holding Test
5. Cough Test
6. DeBono's Whistle Blowing Test
7. Wright's Peak Flow Meter (PEFR measurement)
8. Spirometry with Pocket-Sized Spirometer

1. Snider's Match Blowing Test

• Patient takes a maximal inspiration
• A lighted match is held 15 cm (6 inches) in front of the open mouth
• Patient blows as hard as possible (mouth wide open, not pursed lips)
• Observation: whether the flame is extinguished

• Positive (Able to blow out): FEV1 > 1.6 L (adequate respiratory reserve)
• Negative (Unable to blow out): FEV1 < 1.6 L - suggests significant airflow obstruction
• If patient cannot blow it out at even 6 cm, FEV1 is likely < 1 L - high operative risk
• The test is effort dependent

2. Forced Expiratory Time (FET)

• Patient takes a maximal deep inspiration
• Exhales as hard and fast as possible
• Examiner auscultates over the trachea with a stethoscope and times the duration of audible expiratory airflow

• Normal: < 3 seconds (some say < 4 seconds)
• 3-6 seconds: Borderline / mild obstruction (FEV1/FVC ~ 70%)
• > 6 seconds: Significant obstructive pattern - correlates with FEV1/FVC < 50%

3. Seberese's Single Breath Count (SBC)

• Patient takes a maximal deep breath
• Counts aloud in a normal conversational tone (1, 2, 3, 4...) until they run out of breath

• Normal: > 30 (correlates with VC > 2 L)
• 15-30: Reduced VC (~1-2 L)
• < 15: Severely reduced VC (< 1 L) - high surgical risk
• Each count approximately corresponds to ~100 mL of vital capacity

4. Seberese's Breath Holding Test

• Patient breathes normally for a few cycles
• Takes a maximal deep breath and holds it as long as possible
• Time from full inspiration to next breath is recorded

• Normal: > 25-30 seconds
• 15-25 seconds: Fair reserve (moderate risk)
• < 15 seconds: Poor reserve - high operative risk, likely significant cardiorespiratory compromise

5. Cough Test

• FVC > 20 mL/kg
• FEV1 > 15 mL/kg
• PEFR > 200 L/min
• Vital capacity should be approximately 3x the tidal volume for effective cough generation

• If patient can produce a strong, sharp cough: adequate cough mechanism
• Wet productive cough / self-propagating paroxysms of coughing: suggests susceptibility to pulmonary complications
• Inadequate cough = PEFR < 200 L/min - high risk of postoperative atelectasis and pneumonia

6. DeBono's Whistle Blowing Test

• Patient blows down a wide-bore tube at the end of which is a whistle
• On the side is a hole with an adjustable knob (leak port)
• As the patient blows, the whistle sounds; the leak hole is gradually increased until the whistle sound disappears
• The last position at which the whistle can still be blown is read off a scale

7. Wright's Peak Flow Meter (PEFR Measurement)

• Patient stands or sits upright
• Takes a maximal deep inspiration
• Seals lips around the mouthpiece
• Exhales as hard and fast as possible
• Best of 3 attempts is recorded

• Males: 450-700 L/min
• Females: 300-500 L/min

• PEFR < 200 L/min: impaired cough efficiency - significant risk

• Monitoring asthma control and response to bronchodilators
• Diagnosing airflow obstruction
• Preoperative pulmonary assessment
• Differentiating COPD from CHF (limited utility)

• Effort dependent
• Affected by thoracic/abdominal wound pain
• Only tests large airway patency (does not detect small airway disease)
• Does not measure FVC or provide flow-volume loop data

8. Spirometry with Pocket-Sized (Handheld) Spirometer

1. Calibrate device per manufacturer's instructions
2. Patient stands or sits upright, chin slightly extended
3. Normal breathing for a few cycles
4. Maximal inspiration
5. Seal lips firmly around mouthpiece
6. Exhale as hard and as fast as possible until lungs are completely empty
7. Best of 3 technically acceptable efforts recorded

• Severe respiratory compromise requiring immediate treatment
• Pneumothorax / pneumomediastinum (forced expiration increases intrathoracic pressure)
• Suspected aortic aneurysm or cerebral aneurysm
• Unable to cooperate (unconscious, heavily sedated, children < 4-5 years)

Interpretation of Spirometry Results

Pattern Recognition:

Severity of Obstruction (based on FEV1 % predicted):

Bronchodilator Reversibility:

• Repeat spirometry 15-20 min after bronchodilator (salbutamol 400 mcg)
• Significant reversibility: FEV1 increase of ≥ 12% AND ≥ 200 mL from baseline
• Positive test suggests asthma (reversible obstruction) vs. fixed obstruction (COPD, emphysema)

Indications for Bedside PFTs

1. Preoperative assessment - especially for thoracic, abdominal, upper GI surgeries
2. Acute exacerbations of asthma - to quantify severity and monitor response to treatment
3. Acute COPD exacerbations - though not routinely recommended in guidelines
4. Differentiating dyspnea causes
5. Neuromuscular disease evaluation (e.g., Guillain-Barre, MG)
6. Monitoring chronic lung disease

Preoperative Assessment Criteria (Surgical Risk Stratification)

Summary Table - Bedside PFTs at a Glance

Key Points for MD Exam

1. Forced expiratory time > 6 seconds is the simplest bedside indicator of significant obstructive lung disease
2. PEFR < 200 L/min indicates inadequate cough efficiency and high postoperative pulmonary risk
3. FEV1/FVC < 70% defines obstructive pattern; FVC reduced with normal FEV1/FVC defines restrictive pattern
4. Spirometry with a handheld device provides the most complete bedside assessment - diagnoses type, severity, and bronchodilator reversibility
5. All bedside PFTs (except breath holding) are effort dependent and require patient cooperation
6. Bedside PFTs are suitable for age > 4-5 years, cooperative patients only
7. Bronchodilator reversibility testing distinguishes asthma (reversible) from COPD (partially reversible or fixed)