Review & Interpretation of Pulmonary Function Test (PFT) PDF

Review & Interpretation of Pulmonary Function Test (PFT) By: Ms. Sakinah Almashhed, MsRC, RRT TABLE OF CONTENTS 01 02 03 Introduction Purpose Indications 04 05 06 Spirometry Lung volumes and Diffusion Capacity...

Review & Interpretation of Pulmonary Function Test (PFT) By: Ms. Sakinah Almashhed, MsRC, RRT TABLE OF CONTENTS 01 02 03 Introduction Purpose Indications 04 05 06 Spirometry Lung volumes and Diffusion Capacity capacities INTRODUCTION The ability of the lungs to perform gas exchange depends on the following four general physiologic functions: 1. The diaphragm and thoracic muscles must be capable of expanding the thorax and lungs to produce a sub-atmospheric pressure. 2. The airways must be unobstructed to allow gas to flow into the lungs and reach the alveoli. 3. O2 and CO2 must be able to diffuse through the alveolar capillary membrane. 4. The cardiovascular system must circulate blood through the lungs and ventilated alveoli.  Purpose of PFT The primary purposes of PFT are: Identify pulmonary impairment Quantify the severity of pulmonary impairment if present.  Indications and Contraindications to PFT Indications: Contraindications: To identify and quantify changes in pulmonary Hemoptysis function. Pneumothorax To evaluate the need for therapeutic Acute myocardial infarction or ischemia interventions. Acute pulmonary embolism To assess for postoperative pulmonary Acute chest or abdominal pain complications. Recent cataract surgery Inability to follow instructions There are three basic tests of pulmonary function: Spirometry Lung volumes Diffusing capacity (DL) SPIROMETRY Spirometry is the measurement of air entering and leaving the lungs and includes the measurement of several values of forced airflow and volume during inspiration and expiration. Normal VC may vary as much as 20% above or below the predicted value in healthy individuals based on many factors including: Age Gender Ethnicity Hight Weight When measuring Vital Capacity VC, there are two ways: Slow Vital Capacity SVC Forced Vital Capacity FVC Spirometry Measurements  FVC FVC Acceptability Criteria FVC Repeatability Criteria Maximal effort Three acceptable spirograms Good start-of-test (Back extrapolated volume Two largest FVC and FEV1 values are within less than 5% of FVC or 150 ml Whichever is 150 ml greater) Maximum of 8 trials. No early termination or cutoff (exhalation for If the patient cannot achieve two acceptable maneuvers, the test is terminated 6 seconds or an obvious plateau ) Report the highest FEV1 & FVC values even if they come from separate maneuvers. Reporting Reliable and Valid Results A patient undergoes spirometry testing. A total of three trials are done, all of them deemed to be of good quality and validity. The following results are obtained: Trial 1 Trial 2 Trial 3 Predicted FVC (L) 3.4 3.3 3.5 4 FEV1 (L) 2.7 2.8 2.75 3.6 FEV1/FVC 0.79 0.85 0.76 0.9 Is the test reliable? Which values should be included in the final report? Reporting Reliable and Valid Results Trial 1 Trial 2 Trial 3 Predicted %Predicted FVC (L) 3.4 3.3 3.5* 4 (3.5/4)*100 = 86% FEV1 (L) 2.7 2.8* 2.75 3.6 (2.8/3.6)*100 = 78% FEV1/FVC 0.79 0.85 0.76 0.9 Individual values for FEV1 and FVC are within 0.15 L of each other, so the test is considered reliable. The best FEV1 and the best FVC should be reported*, even if they came from different trials. The report should also include percent predicted values for FEV1 and FVC, which is calculated by dividing the “best” value by the “predicted” value.  Detecting Abnormalities Obstructive Restrictive Mixed FVC Normal Reduced Reduced FEV1 Reduced Reduced Reduced FEV1% Reduced Normal or elevated Reduced (FEV1/FVC × 100) * TLC Normal or Less than 80% of predicted Reduced elevated normal * FEV1% is the 1ST step to assess airway obstruction Pulmonary Dysfunction detection by the Flow volume loop Pre and Post Bronchodilator Tests The test is used to determine airflow-limitation reversibility with drug administration, or whether the patient’s lung function can be improved with therapy in addition to their regular treatment. Technique: 1. Obtain baseline values (three acceptable results of FVC, FEV1, FEV1%) 2. Administer bronchodilator (Wait for the medication response) 3. Reassess lung function (re-obtain 3 acceptable results) 4. Interpret the results An increase in FEV1 and/or FVC > 10% from baseline values is considered positive Calculation: % change = [(Post drug – Pre drug)/Pre drug] *100  How to Interpret the Airway Function? FEV1/FVC%