Lecture: Pulmonary Function Tests (PFTs) – For 2nd Year Anaesthesia Technology Students
Pulmonary Function Tests (PFTs)
A Lecture for 2nd Year Anaesthesia Technology Students
1. Introduction
Pulmonary Function Tests (PFTs) are a group of non-invasive diagnostic procedures used to assess respiratory function. For anaesthesia technologists, understanding PFTs is essential because they help in preoperative assessment, intraoperative management, and postoperative care of patients—especially those with known or suspected pulmonary disease.
2. Objectives
- Understand the types and principles of common PFTs.
- Interpret basic PFT parameters relevant to anaesthesia.
- Recognize the clinical significance of abnormal PFT results in surgical patients.
- Appreciate the role of the anaesthesia technologist in PFT preparation and monitoring.
3. Types of Pulmonary Function Tests
3.1 Spirometry
The most common PFT. It measures:
- Forced Vital Capacity (FVC): Total volume of air exhaled forcefully after full inspiration.
- Forced Expiratory Volume in 1 second (FEV₁): Volume exhaled in the first second.
- FEV₁/FVC ratio: Key indicator to differentiate obstructive vs. restrictive lung disease.
3.2 Lung Volumes and Capacities (via Body Plethysmography or Gas Dilution)
- Total Lung Capacity (TLC)
- Residual Volume (RV)
- Functional Residual Capacity (FRC)
These help diagnose restrictive lung diseases (e.g., pulmonary fibrosis) where spirometry alone may be insufficient.
3.3 Diffusing Capacity of the Lungs for Carbon Monoxide (DLCO)
Measures gas transfer across the alveolar-capillary membrane. Reduced in:
- Emphysema
- Interstitial lung disease
- Pulmonary vascular disease
3.4 Maximal Voluntary Ventilation (MVV)
Assesses the maximum volume of air a patient can breathe in and out in one minute. Useful for evaluating respiratory muscle strength and endurance—critical in predicting postoperative respiratory complications.
4. Interpretation of PFTs: Obstructive vs. Restrictive Patterns
| Parameter | Obstructive Disease (e.g., COPD, Asthma) | Restrictive Disease (e.g., Fibrosis, Scoliosis) |
|---|---|---|
| FEV₁ | ↓↓ | ↓ |
| FVC | Normal or ↓ | ↓↓ |
| FEV₁/FVC | < 0.7 (or < lower limit of normal) | Normal or ↑ |
| TLC | Normal or ↑ | ↓↓ |
5. Relevance to Anaesthesia Practice
- Preoperative Risk Assessment: Patients with FEV₁ < 1.0 L or < 50% predicted are at high risk for postoperative pulmonary complications.
- Airway Management: Severe obstruction may affect rapid sequence induction and ventilation.
- Mechanical Ventilation Settings: Knowledge of FRC and compliance guides PEEP and tidal volume selection.
- Postoperative Monitoring: Patients with low MVV or DLCO may need extended ventilatory support or ICU admission.
6. Role of the Anaesthesia Technologist
- Assist in preoperative PFT data collection and verification.
- Ensure proper calibration and readiness of spirometers or PFT equipment if used intraoperatively (e.g., in lung resection).
- Monitor real-time respiratory parameters during anaesthesia that reflect underlying pulmonary function (e.g., dynamic compliance, airway pressures).
- Educate patients on incentive spirometry postoperatively to prevent atelectasis.
7. Limitations and Considerations
- PFTs require patient cooperation—may be unreliable in children, elderly, or cognitively impaired patients.
- Acute illness (e.g., bronchitis, pneumonia) can temporarily alter results.
- Always correlate PFTs with clinical findings, imaging, and arterial blood gas analysis.
References
- Miller, R. R. (Ed.). (2023). Miller’s Anesthesia (10th ed.). Elsevier. – Chapters on Pulmonary Physiology and Preoperative Evaluation.
- Macintyre, N., Crapo, R. O., Viegi, G., et al. (2005). Standardisation of the single-breath determination of carbon monoxide uptake in the lung. European Respiratory Journal, 26(4), 720–735. https://doi.org/10.1183/09031936.05.00034905
- American Thoracic Society/European Respiratory Society. (2019). Standardization of Spirometry. American Journal of Respiratory and Critical Care Medicine, 200(10), e70–e88. https://doi.org/10.1164/rccm.201908-1590ST
- Murray, J. F., & Nadel, J. A. (2022). Textbook of Respiratory Medicine (7th ed.). Elsevier.
- National Heart, Lung, and Blood Institute (NHLBI). (2023). Pulmonary Function Tests. https://www.nhlbi.nih.gov/health/pulmonary-function-tests
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