PULMONARY FUNCTION TESTING

Transcription

1 by Michael R. Carr, BA, RRT, RCP and Helen Schaar Corning, RRT, RCP RC Educational Consulting Services, Inc Van Buren Blvd, Suite B, Riverside, CA (800) 441-LUNG / (877) 367-NURS

2 BEHAVIORAL OBJECTIVES UPON COMPLETION OF THE READING MATERIAL, THE PRACTITIONER WILL BE ABLE TO: 1. List the primary indications for pulmonary function tests (PFT s). 2. Explain ATPS/BTPS and ATS standards. 3. Differentiate between lung volumes and lung capacities. 4. For each lung capacity, list the volumes contained therein. 5. List the normal values of each lung capacity. 6. Identify the normal values of each lung volume. 7. Explain what spirometry is. 8. Describe the volumes and flow rates that can be determined by spirometry. 9. List the lung volumes that cannot be measured by spirometry. 10. Identify the special procedures used in Pulmonary Function Testing. 11. Summarize the DLCO procedure. 12. Explain body plethysmography. 13. List the purpose of performing the helium dilution and nitrogen washout. 14. Describe the pulmonary angiogram or arteriogram. 15. List the main purpose of a V/Q scan. 16. Demonstrate ability to differentiate obstructive and restrictive disorders based on PFT results. 17. Explain the normal and abnormal range in percent of predicted values. 18. Specify the formula for ideal body weight (IBW). 19. List the formula calculating the oxygen index. 20. Describe how to calculate the P/F ratio. This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 2

3 COPYRIGHT 2006 BY RC EDUCATIONAL CONSULTING SERVICES, INC. TX Authored by: Michael R. Carr, BA, RRT, RCP and Helen Schaar Corning, RRT, RCP (2006) ALL RIGHTS RESERVED This course is for reference and education only. Every effort is made to ensure that the clinical principles, procedures and practices are based on current knowledge and state of the art information from acknowledged authorities, text and journals. This information is not intended as a substitution for diagnosis or treatment given in consultation with a qualified health care professional. This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 3

4 TABLE OF CONTENTS INTRODUCTION... 7 PRIMARY INDICATIONS FOR PULMONARY FUNCTION TESTS... 7 PFT MEASUREMENT STANDARDS... 8 ATPS / BTPS... 8 ATS STANDARDS... 8 DESCRIPTIONS OF LUNG VOLUMES AND LUNG CAPACITIES... 9 LUNG CAPACITIES LUNG VOLUMES SPIROMETRY FORCED VITAL CAPACITY MEASUREMENTS FORCED EXPIRATORY VOLUME TIMED (FEVt) SPECIAL PROCEDURES IN PULMONARY FUNCTION TESTING DLCO - GAS DIFFUSION TESTING BRONCHIAL PROVOCATION TESTS MEASURING RESIDUAL VOLUME, FUNCTIONAL RESIDUAL CAPACITY, AND TLC BODY PLETHYSMOGRAPH HELIUM DILUTION TEST (CLOSED CIRCUIT) NITROGEN WASHOUT TEST (OPEN CIRCUIT) GAS/BLOOD FLOW DISTRIBUTION TESTING: SINGLE BREATH NITROGEN ELIMINATION (SBN 2 ) DESCRIPTIONS OF MISCELLANEOUS PULMONARY MECHANICS MAXIMUM VOLUNTARY VENTILATION (MVV) OR MAXIMUM BREATHING CAPACITY (MBC) This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 4

5 PEAK FLOW (PF) OR PEAK EXPIRATORY FLOW RATE (PEFR) MAXIMAL EXPIRATORY PRESSURE (MEP) MAXIMAL INSPIRATORY PRESSURE (MIP) AND NEGATIVE INSPIRATORY FORCE (NIF) INCENTIVE SPIROMETRY (IS) INTERPRETING PFT RESULTS BASED ON PERCENT OF PREDICTED VALUE ASSESSING POST BRONCHODILATOR % IMPROVEMENT CALCULATIONS USED IN PFT MEASUREMENTS HEIGHT AND WEIGHT CONVERSIONS IDEAL BODY WEIGHT (IBW) BODY SURFACE AREA M 2 (BSA) BODY MASS INDEX (BMI) BASAL METABOLIC RATE (BMR) AND RESTING ENERGY EXPENDITURE (REE) OXYGEN INDEX (OI) BRIEF REVIEW OF ARTERIAL BLOOD GASES (ABG S) NORMAL VALUES INTERPRETATION MOST COMMON CAUSES OF ABNORMAL BLOOD GASES RESPIRATORY ACIDOSIS RESPIRATORY ALKALOSIS METABOLIC ACIDOSIS This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 5

6 METABOLIC ALKALOSIS CONCLUSION CLINICAL PRACTICE EXERCISE APPENDIX SUGGSTED READING AND REFERENCES This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 6

7 INTRODUCTION Respiratory therapists are often asked to perform pulmonary function (PF) testing in different areas of the hospital and oversee the pulmonary function laboratory. Pulmonary function testing offers many opportunities for a respiratory therapist because the indications for testing are many and the tests are currently under-used by most physicians. The pulmonary function technician (respiratory therapist) is responsible for explaining the testing procedure to the patient and coaching the patient in order to obtain the best possible results. The results are then documented and given to the attending physician for interpretation and follow-up treatment if needed. Evaluation of pulmonary function benefits many types of patients. Pulmonary disease may frequently be detected by PF tests years before the onset of signs or symptoms. Early detection of pulmonary disease helps the physician convince patients to stop smoking, reducing the risk of both cardiovascular and pulmonary disease. Test comparison helps the physician to determine whether a specific therapeutic regimen is beneficial. Shortness of breath is a common complaint for which PF tests can help differentiate between a cardiac and a pulmonary cause. The PF tests performed before planned surgery help to reduce the incidence of postoperative pulmonary complications by identifying patients at increased risk. Finally, patients who feel that their ability to work is limited by shortness of breath can be objectively evaluated by PF tests. The results often carry considerable legal and economic consequences. This course describes the tests respiratory therapists should be familiar with even if they do not work in a pulmonary function laboratory. It is not uncommon for a patient to be admitted to the hospital who has had previous PFT that is reported in the current chart. A quick review of these results may be instrumental in decision making about current treatment. In addition to defining the common pulmonary function tests performed, a brief discussion of what may cause abnormalities in the results is included. PRIMARY INDICATIONS FOR PULMONARY FUNCTION TESTS Assessment of the respiratory system Test for the presence of lung disease Identify the type of lung disorder (Obstructive vs. Restrictive) Aid in identifying location of disorder (small vs. large airways) Evaluate the extent of pulmonary dysfunction Assess progression of lung disease Aid in establishing a therapeutic regimen for the dysfunction This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 7

8 PFT s are used to assess the respiratory system. PFT s can also aid in differentiating between obstructive and restrictive lung diseases. Obstructive pulmonary disease includes asthma, bronchitis, bronchiectasis, emphysema, cystic fibrosis, and bronchopulmonary dysplasia. Most other lung disorders are classified as restrictive pulmonary diseases. Some of the most common restrictive diseases include pneumonia, pneumothorax, pulmonary edema, pleural effusion, myasthenia gravis, and adult respiratory distress syndrome (ARDS). PFT MEASUREMENT STANDARDS ATPS / BTPS Volumes measured by spirometry are at ambient temperature, pressure, and saturated (ATPS) conditions. These measurements are then adjusted for the temperature difference between the spirometer and the patient s body temperature, pressure, and saturated conditions (BTPS). ATS Standards ATS standards are guidelines that safeguard against procedural errors, and help assure accurate results. An important factor in meeting ATS standards are to perform equipment calibration, maintenance, and cleaning on a regular schedule. Equipment can go out of calibration, on its own, whether frequently or rarely used. Also, particulate matter can buildup inside the machine causing it to go out of calibration. It is important to calibrate PFT equipment on schedule to assure results are valid. One must follow the manufacturer s calibration, maintenance, and cleaning schedules, as well as the employing institution s policies. One example of calibrating spirometers involves injecting a known amount of air into the spirometer, and testing for a readout result of the same value. A 3-liter super syringe is often utilized for this calibration. Another important point involving PFT s is that many tests are very effort dependent. The patient must be motivated to put forth the very best effort. The patient must be thoroughly instructed on the procedure before the test, and given three attempts when appropriate. This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 8

9 PFT GRAPHIC DISPLAY OF LUNG VOLUMES AND CAPACITIES IC IRV TLC VC / FVC VT FRC ERV RV RV DESCRIPTIONS OF LUNG VOLUMES AND LUNG CAPACITIES I n the field of pulmonary function testing (PFT), the air within the lungs is divided into segments called capacities and volumes. Each lung capacity contains two or more lung volumes. The reason for assessing the air this way is to more accurately measure specific lung functions in different areas of the lungs. There are many different pulmonary diseases, and a broad range of PFT s are required to assess and diagnose pulmonary dysfunctions. The total lung capacity (TLC) is a measurement of the total volume of air contained in the lungs. The total lung capacity contains two segments: the vital capacity (VC), and the residual volume (RV). Therefore VC plus RV equals TLC. The vital capacity (VC) is a measurement of the maximum volume of air that can be exhaled after a maximal inspiration. Forced vital capacity (FVC) is the same in volume as the VC, but the patient is asked to exhale as quickly and forcefully as possible. The FVC is performed when one wants to assess flow rates. The residual volume (RV) is the volume of air remaining in the lungs after a maximal exhalation. Measuring the RV requires special testing, as this air cannot be measured by spirometry. Since residual volume is a part of the total lung capacity, measurement of the TLC also requires special testing. The total lung capacity contains the inspiratory capacity (IC) and the functional residual capacity (FRC). Therefore IC plus FRC equals TLC. The inspiratory capacity is the maximum amount of air that can be inhaled after a normal tidal volume exhalation. The functional residual capacity is the amount of air remaining in the lungs after a normal tidal volume exhalation. This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 9

10 The inspiratory capacity is divided into two volumes: the inspiratory reserve volume (IRV) and the tidal volume (VT). The IRV is the maximum volume of air than can be inhaled after a normal tidal volume inspiration. The VT is the volume of air that is inhaled and exhaled during normal quiet breathing. The functional residual capacity is divided into two volumes called the expiratory reserve volume (ERV), and the residual volume (RV). The ERV is the amount of air than can be exhaled after a normal tidal volume exhalation. PFT ABBREVIATIONS AND DESCRIPTIONS 35 Lung Capacities Lung Capacity (contains two or more volumes) TLC Total Lung Capacity VC Vital Capacity or FVC Forced Vital Capacity IC Inspiratory Capacity FRC Functional Residual Capacity Description Total volume of air contained in the lungs. TLC = IC + FRC. Also TLC = VC + RV. Also TLC = VT + IRV + ERV + RV. Maximum volume of air that can be exhaled after a maximal inhalation. VC = VT + IRV + ERV. FVC is equal in volume to VC, but the patient must exhale as quickly and forcefully as possible in order to assess flow-rates. Maximum amount of air that can be inspired after a normal VT exhalation. IC = VT + IRV. Volume of air remaining in the lungs after a normal VT exhalation. FRC = ERV + RV. Includes RV air-trapping, which cannot be measured by simple spirometry, requires special testing. Increased FRC or increased RV/TLC ratio (> 20%) indicates an obstructive disorder. Decreased FRC and TLC indicates restrictive disorder. Lung Volumes Lung Volume VT or TV Tidal Volume IRV Inspiratory Reserve Volume ERV Expiratory Reserve Volume Description Volume of air that is inhaled and exhaled during normal quiet breathing. Maximum volume of air than can be inhaled after a normal VT inspiration. Maximum volume of air than can be exhaled after a This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 10

11 normal VT exhalation. RV Residual Volume RV/TLC Ratio Volume of air remaining in the lungs after a maximal exhalation. Includes air-trapping, which cannot be measured by simple spirometry, requires special testing. Increased FRC or increased RV/TLC ratio (> 20%) indicates an obstructive disorder. Decreased FRC and TLC indicates restrictive disorder. The following table lists the calculations for normal values for each of the lung capacities and volumes mentioned above. NORMAL PFT VALUES AND CALCULATIONS FOR ADULTS* 35 Volumes and Capacities Calculation for Normal Values Normal Values for 60 Kg Female Normal Values for 70 Kg Male TLC 80 ml/kg 4800 ml 5600 ml VC or FVC 65 ml/kg 3900 ml 4550 ml IC 50 ml/kg 3000 ml 3500 ml FRC 30 ml/kg 1800 ml 2100 ml VT 7 ml/kg 420 ml 490 ml IRV 40 ml/kg 2400 ml 2800 ml ERV 17 ml/kg 1020 ml 1190 ml RV RV/TLC ratio SPIROMETRY 16 ml/kg 20% of TLC 960 ml 20% of TLC Spirometry can measure: VC/FVC, IC, IRV, VT, ERV, and flow rates ml 20% of TLC Spirometry cannot measure: RV, FRC, and TLC. These require special testing, covered later in this course. FORCED VITAL CAPACITY MEASUREMENTS The forced vital capacity is a commonly utilized tool for assessing lung function. This FVC aids in diagnosing both restrictive and obstructive pulmonary diseases. The FVC can also help pinpoint the location of the dysfunction in the small or large airways. The FVC also gives flow rate results. Flow rates are calculations of the amount of time it takes to exhale air. The patient inhales as deeply as possible, then exhales as quickly and forcefully as possible. Patients are usually given three attempts, and the best of the three results are used to This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 11

12 calculate the flow rates. The flow rates also aid in determining whether a small or large airway dysfunction is present. PFT Flow Rates and Time% FEV 0.5 FEV 0.5/%FVC FEV 1.0 FEV 1/%FVC FEV 2.0 FEV 2/%FVC FEV 3.0 FEV 3/%FVC FEF or MEFR FEF 25-75% or MMFR Description Forced Expiratory Volume in first 0.5 seconds of FVC. 0.5 Time% normally 60% of FVC. Forced Expiratory Volume in first 1.0 seconds of FVC. 1.0 Time% normally 80% of FVC. Forced Expiratory Volume in first 2.0 seconds of FVC. 2.0 Time% normally 94% of FVC. Forced Expiratory Volume in first 3.0 seconds of FVC. 3.0 Time% normally 97% of FVC. Forced Expiratory Flow after first 200 ml exhaled, until next 1200 ml exhaled during FVC. Also called Maximum Expiratory Flow Rate. Measures function of large airways. Forced Expiratory Flow rate over middle 50% of FVC. Also called Maximal Mid-Expiratory Flow Rate. Measure function of small and medium airways. The following table lists the calculations for normal values for the flow rates listed above. 36 Flow Rates and Time% Calculation for Normal Values Normal Values for 60 Kg Female Normal Values for 70 Kg Male FEV 0.5 seconds 60% of FVC 2340 ml 2730 ml FEV 1.0 seconds 80% of FVC 3120 ml 3640 ml FEV 2.0 seconds 94% of FVC 3670 ml 4280 ml FEV 3.0 seconds 97% of FVC 3780 ml 4410 ml FEF or MEFR 6 L/sec 360 L/min 360 L/min FEF 25-75% or MMFR 4.7 L/sec 280 L/min 280 L/min Forced Expiratory Volume Timed (FEVt) The forced expiratory volume timed (FEVt) is the volume of air measured at specific timed intervals during the FVC test. Measurements are taken at 0.5 seconds (FEV 0.5), at 1.0 seconds (FEV 1.0), at 2.0 seconds (FEV 2.0), and at 3.0 seconds (FEV 3.0). Another measurement of the FVC is given in a timed percentage of the vital capacity (FEVt%). This is the percentage of air exhaled during an FVC. The FEF 25%-75% (also called maximal mid- expiratory flow rate) is a This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 12

13 good spirometry test for detecting small airway disease. To assess the function of the large airways, the forced expiratory flow-rate is measured between 200 ml and 1200 ml of the total air exhaled during the FVC. This is called the FEF , or the MEFR, which stands for the Maximum Expiratory Flow Rate. SPECIAL PROCEDURES IN PULMONARY FUNCTION TESTING 37 DLCO - Gas Diffusion Testing This test measures the factors that affect the diffusion of air across the alveolar-capillary (A/C) membrane. The test aids in diagnosing reduced surface area for diffusion. The most common test used is the carbon monoxide diffusion capacity or DLCO (Lung Diffusion for Carbon Monoxide). The patient inspires as deeply as possible, breathing in a small concentration of carbon monoxide mixed with helium and air. The patient then must hold the breath for ten seconds, then exhale into a device that analyzes the gas concentrations and calculates the diffusion capacity. The normal value for a single breath DLCO is 25 ml/minute/mmhg. A variation of this test is the steady state DLCO test, in which the patient breathes normally for three minutes, inhaling a mixture of carbon monoxide, helium, and air. The measurement is taken during the third minute. The normal DLCO steady state value is 17 ml/minute/mmhg. The DLCO used in conjunction with the FVC is the most useful PFT for detecting emphysema. The DLCO value is reduced in emphysema and also in some restrictive diseases, including pulmonary fibrosis and sarcoidosis. Bronchial Provocation Tests Some patients have normal spirograms with all the symptoms of asthma or an undiagnosed cough. These people often have reactive airways disease (RADS). Bronchial provocation is an easy and save way to make a differential diagnosis. Challenging the patient with inhaled histamine or methacholine is most commonly used. A. Use of bronchial provocation test 1. To assess patients with normal PFT s and symptoms of bronchospasm. 2. To quantify severity of asthma and assess changes in airway reactivity. 3. Screening of those who may be at risk from or to document the effects of environmental or occupational exposure to toxins, B. Patients must be asymptomatic at baseline C. Bronchodilators and antihistamines must be withheld before the test. Inhaled corticosteroids should not be withheld D. Appropriate emergency equipment and monitoring devices should be readily available This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 13

14 E. Baseline spirometry test are measured before the challenge and compared with serial spirometry measurements taken at specified time intervals after the challenge F. Methacholine challenge (adapted from the AARC Clinical Practice Guidelines) 1. Baseline FEV 1 measurements are made before the administration of the aerosolized drug and after each successive dose is administered. 2. The first dose of methacholine administered is mg/ml. The dose used for each subsequent administration is determined using a predetermined dosing schedule. Dosing schedules commonly specify doubling the dose each time, up to a maximum of 25 mg/ml. 3. The methacholine concentration that causes a 20% decrease in the FEV 1 from baseline is referred to as the provocative dose or PD 20%. 4. The test is stopped once PD 20% is reached. 5. Normal, healthy subjects have a PD 20% that is greater than the maximum dose used foe testing. These individuals do not show a 20% decrease in FEV 1 during a methacholine challenge. 6. A PD 20% of < 8 mg/ml is common in patients with hyperreactive airways. Measuring Residual Volume, Functional Residual Capacity, And TLC Measuring the residual volume requires special testing as it cannot be measured by spirometry. Since the RV is a part of the FRC and the TLC, these measurements also require special testing. The RV measurement includes air that is trapped in the lungs after a maximal exhalation, and can help differentiate between obstructive and restrictive lung disease. An increased FRC or an increased RV/TLC ratio (more than 20%) indicates an obstructive disorder. If the TLC and the FRC are decreased, this indicates a restrictive disorder. Body Plethysmograph Also called the body box, this is the most accurate method for measuring the FRC. This test can measure the total thoracic gas volume (TGV), including air trapped in the smallest airways. The patient sits inside of the body plethysmograph and pants against a closed shutter, at a rate of approximately 2 breaths per second, while the pressures and volumes are obtained. The TGV is increased in obstructive disease, and decreased in restrictive disorder. Helium Dilution Test (Closed Circuit) Another method of measuring the FRC is the closed circuit helium dilution method. The patient breathes a mixture of air with 10% helium. The helium is diluted by the breathing until equilibrium takes place at approximately five to seven minutes. A percentage of that helium is diluted by the patient s FRC, and the change in helium percentage is measured to determine the FRC. If equilibrium takes longer (up to 20 min), it indicates obstructive disease. The FRC is increased in obstructive disease, and decreased in restrictive disorder. The helium dilution test is fairly accurate, but if there is a large amount of air trapped in the patient s lungs, a small amount of air may be left undetected. This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 14

15 Nitrogen Washout Test (Open Circuit) Another method of measuring the FRC, and aid in detecting a pulmonary embolism is the nitrogen washout. In this test, the patient breathes 100% oxygen for about 7 minutes exhaling all gas into an analyzer, and a breath-by-breath curve is obtained. Then patient exhales completely. Fractional concentration of alveolar nitrogen (FAN 2 ) is noted, and the FRC is computed. The FRC is increased in obstructive disease, and decreased in restrictive disorder. After 7 minutes, the normal amount of nitrogen remaining in the lungs is less than 2.5%. If greater than 2.5% nitrogen remains at 7 minutes, this indicates poor distribution of ventilation, obstructive disorder, or possible pulmonary embolism. Gas/Blood Flow Distribution Testing: Single Breath Nitrogen Elimination (SBN 2 ) The single breath nitrogen elimination test measures the evenness of distribution of inspired gases. This test is very sensitive for detecting early airway closure, small airway obstructions, and pulmonary embolism. The patient exhales maximally, then inhales 100% oxygen maximally, followed by slowly exhaling the gas until the lungs feel empty. The exhaled gas passes through a nitrogen analyzer that measures the change in the concentration of nitrogen. The first 750 ml of air exhaled is mostly deadspace, and is discarded (phase I and II). The next 500 ml of exhaled air (phase III) is used for measurement of nitrogen distribution. The rise of nitrogen percentage in phase III should be less than 1.5%. A higher percentage represents uneven distribution, with a possible pulmonary embolism. This test also includes the closing volume test (CV) and closing capacity test (CC) as listed in the following table. The following table lists the special procedures used in PFT testing that are discussed above in a brief reference format. Additionally, this table includes the Flow-Volume Loop, Volume of Isoflow, Pulmonary Angiogram or Arteriogram, and the Ventilation/Perfusion (V/Q) scan. TABLE OF PFT SPECIAL PROCEDURES 39 Test Normal Value Description Single breath DLCO 25 ml/minute/mmhg DLCO Lung Diffusion for Carbon Monoxide or Gas Diffusion Testing Body Plethysmograph or Steady state DLCO 17 ml/minute/mmhg Normal predicted values for TGV, TLC and FRC Measures factors that affect diffusion of air across A-C membrane; detects if surface area for diffusion is reduced. Patient inhales small concentration of carbon monoxide, helium and air. Patient exhales into device that analyzes gas concentrations and calculates DLCO. DLCO reduced in emphysema, pulmonary fibrosis, embolism, and sarcoidosis. Most accurate method for measuring FRC, RV, and TLC. Measures total This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 15

16 Body Box or TGV Thoracic Gas Volume Helium Dilution (closed circuit) Nitrogen Washout (open circuit) SBN 2 Single Breath Nitrogen Elimination Includes: Closing Volume (CV) and Equilibrium at <= 7 minutes. Normal FRC. Less than 8 minutes to reach less than 2.5% nitrogen in lungs. Normal FRC. Phase III N 2 rise should be less than 1.5%. TGV, including air trapped in smallest airways. Patient pants at FRC against closed shutter, at about 2 breaths per second, while pressures and volumes are measured. TGV increased in obstructive disease, decreased in restrictive disorder. Method of measuring the FRC, then calculating RV and TLC; not as accurate as plethysmograph for detecting trapped air. Patient breathes mixture of air with 10% helium, until equilibrium takes place at 5-7 minutes. If equilibrium takes longer (up to 20 min), it indicates obstructive disease. FRC increased in obstructive disease, decreased in restrictive disorder. Method of calculating the FRC, and RV; not as accurate as plethysmograph for detecting trapped air. Also measures evenness of distribution of ventilation, w/breath-by-breath curve. Patient breathes 100% O 2 for about 7 minutes, exhaling all gas into an analyzer, until nitrogen remaining in lungs is less than 2.5%. Then patient exhales completely. Fractional concentration of alveolar nitrogen (FAN 2 ) is noted, and FRC is computed. Greater than 7 minutes to reach 2.5% nitrogen remaining in lungs indicates poor distribution of ventilation, obstructive disorder, or possible pulmonary embolism. Calculated FRC increased in obstructive disease, decreased in restrictive disorder. Measures the evenness of distribution of inspired gases. Patient exhales maximally, inspires 100% O 2 maximally, then slowly exhales the gas until lungs feel empty. The exhaled gas passes through N 2 analyzer that measures the change in concentration of nitrogen. The first 750 ml of air This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 16

17 Closing Capacity (CC) exhaled is mostly deadspace, and is discarded (phase I and II). The next 500 ml of exhaled air (phase III) is used to measure distribution. The rise of N 2 percentage in phase III should be less than 1.5%. A phase III N 2 rise > 1.5% indicates uneven distribution of ventilation or uneven flow rates, with possible pulmonary embolism. Flow-Volume Loop** Volume of Isoflow VisoV and Vmax50 Normal volumes and flow rates as predicted. Pulmonary Angiogram or... CV is Phase IV. CV should = 10-20% of VC. CC is Phase V. CC should = 30-40% of TLC. CV% increased in small airway obstruction. Very sensitive for detecting early airway closure. Measures the volumes and flow rates of the vital capacity. Expiratory flow above baseline, inspiratory flow below baseline. Patient inspires to TLC, exhales forcefully for FVC, then inhales maximally to TLC again. Graphic loop results. Can detect obstructive and restrictive patterns, decreased volumes, decreased flow rates, airway resistance and small airway disease % of VC. Consists of 2 maximal expiratory flow curves. First FVC uses air. Second FVC uses O 2 20% + helium 80%. Volume remaining in lungs after 2 nd FVC is the volume of isoflow, normally 10-20% of VC. VisoV increased in small airway disease. Vmax50 measures flow at 50% of the VC, similar to FEF 25-75%. Vmax50 measures changes in airway resistance in small and medium airways. Measures blood flow distribution. Radio-graphic study of the arteries after injecting radiopaque dye. Motion and This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 17

18 Arteriogram V/Q scan or Ventilation/perfusion scan... still pictures are obtained, with observation of blood flow through blood vessels. Can detect unperfused blood vessels, and pulmonary embolism. Measures gas and blood flow distribution (ventilation and perfusion). Involves inhalation of radiolabeled gas (xenon), and injection of radioisotope, followed by study of mismatches between ventilation and perfusion. Can detect poorly ventilated areas, unperfused blood vessels, and pulmonary embolism. MEASURING MISCELLANEOUS PULMONARY MECHANICS The following is a table listing the normal values for pulmonary mechanics that will be discussed next. 35 Misc. Pulmonary Mechanics Calculation for Normal Values Normal Values for 60 Kg Female Normal Values for 70 Kg Male MVV or MBC L/min 150 L/min 170 L/min PF Peak Flow or PEFR L/min 400 L/min 600 L/min MEP >= + 80 cmh 2 O >= + 80 cmh 2 O >= + 80 cmh 2 O MIP or NIF 80 to 100 cmh 2 O 80 to 100 cmh 2 O 80 to 100 cmh 2 O IS 50 ml/kg 3000 ml 3500 ml * Normal values based on normal adults with ideal body weight (IBW). Normal value calculation factors also include age, height, sex, and race. Normal values decrease with age. DESCRIPTIONS OF MISCELLANEOUS PULMONARY MECHANICS Maximum Voluntary Ventilation (MVV) Or Maximum Breathing Capacity (MBC) The maximum voluntary ventilation (MVV), also called the maximum breathing capacity (MBC), gives information on the status of respiratory muscles, and measures compliance and resistance. The patient is instructed to breathe as deep and as fast as possible for seconds into a spirometer with an accumulator recording. The maneuver exaggerates airtrapping. The value is then converted into minutes, with the normal value of 150 to 170 liters per minute for an average adult. This test is very sensitive and can give an indication of an obstructive disease in the early stages. Results are decreased in obstructive diseases. Results can be normal with a mild restrictive disease, but are decreased in a severe restrictive disease. This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 18

19 Peak Flow (PF) Or Peak Expiratory Flow Rate (PEFR) Peak Flow (PF) or Peak Expiratory Flow Rate (PEFR) is a test in which the patient inhales as deeply as possible, then blows all the air out of their lungs as fast as possible. (This procedure is basically the same as the FVC, but the PEFR only calculates one value instead of the many values calculated during an FVC maneuver.) For an average adult, the normal PEFR is approximately liters per minute. This test can be done with a simple and portable handheld peak flow meter. The test is typically used by asthmatic and other COPD patients to monitor their respiratory status. The PEFR is also frequently utilized in emergency rooms to quickly assess the pulmonary status of patients. PFT s are also used to assess a patient s response to bronchodilator therapy. Pre- and post- bronchodilator testing of the FVC flow-rates, or the PEFR, give a reliable indication of the effectiveness of the bronchodilator. Maximal Expiratory Pressure (MEP) The maximal expiratory pressure (MEP) is a test to assess respiratory muscle strength. The patient inhales deeply, then blows all of their air into the device to measure peak expiratory pressure. The normal value is greater than or equal to 80 cmh 2 O. Maximal Inspiratory Pressure (MIP) And Negative Inspiratory Force (NIF) The maximal inspiratory pressure (MIP) and the negative inspiratory force (NIF) are the same type of maneuver that can be performed on the MIP or the NIF device. The MIP or NIF is done to assess respiratory muscle strength. The patient inhales maximally with a short breath hold, and the peak inspiratory pressure is measured. The normal MIP or NIF is -80 to -100 centimeters of water. A value of -20 cm H 2 O or better is the minimal acceptable value at which ventilator weaning is attempted. The NIF is also commonly utilized to assess for impending respiratory failure as in myasthenia gravis and Guillian-Barré patients. These patients have neuromuscular disorders that can cause extreme weakness or paralysis of the respiratory muscles. Here, the VC and NIF are used in conjunction at set time intervals to monitor these patients. When values are decreasing below the normal range, it can indicate impending respiratory failure. Incentive Spirometry (IS) Incentive spirometry is used both as a lung exercise device and a tool for measuring inspiratory respiratory muscle strength. Incentive spirometry has proven to improve lung aeration and prevent atelectasis. The normal values for IS are the same as for inspiratory capacity (IC) at 50 ml/kg of ideal body weight. The patients are instructed to inhale on the device as deeply as possible and perform a five second breath hold approximately ten times every one to two hours while awake. The normal value for the patient s are calculated by a clinician, and patients can then be instructed how to monitor their own values. This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 19

20 INTERPRETING PFT RESULTS OBSTRUCTIVE VS. RESTRICTIVE DISEASE PATTERNS 36 Volumes and Capacities Obstructive Disease Restrictive Disorder TLC VC or FVC N or IC N or N or FRC N or VT Varies N or IRV N or ERV N or N or RV N or FEV 0.5 seconds N or FEV 1.0 seconds N or FEV 2.0 seconds N or FEV 3.0 seconds N or FEF N or FEF 25-75% N or MVV or MBC N or PF Peak Flow N or * N = Normal Obstructive disease pattern: Decreased flow rates, increased RV, increased TLC. Restrictive disease pattern: Decreased volumes, decreased TLC. Obstructive pulmonary diseases include asthma, bronchitis, bronchiectasis, emphysema, cystic fibrosis, and bronchopulmonary dysplasia. Most other lung dysfunctions are restrictive pulmonary disorders. Interpreting PFT Results Based on Percent of Predicted Value: Normal: Mild disorder: Moderate disorder: Severe disorder: % of predicted % of predicted % of predicted. Less than 50% of predicted. Assessing Post Bronchodilator % Improvement: Non-significant improvement: Less than 15% Significant improvement: 15% or greater. (Very large improvements may be indicative of asthma.) This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 20

21 CALCULATIONS USED IN PFT MEASUREMENTS 36, 37 HEIGHT AND WEIGHT CONVERSIONS Height Inches (in) To Centimeters (cm) Conversion Calculation: Convert Inches to Centimeters: in x 2.54 = cm Convert Centimeters to Inches: cm 2.54 = in Inches cm Inches cm Inches cm in = 4 feet 60 in = 5 feet 72 in = 6 feet Ideal Body Weight (IBW) Female: (5 x height in inches over 60) Example: 65 inch tall female has an IBW of 130 lb: (5 x 5) Male: (6 x height in inches over 60) Example: 70 inch tall male has an IBW of 166 lb: (6 x 10) Body Surface Area m 2 (BSA) Calculation: Square root of: Height (in) x Weight (lb) 3131 or Square root of: Height (cm) x Weight (kg) 3600 Sample: Find the BSA of a 65 inch tall 130 lb female: 1.6 m 2 Body Mass Index (BMI) Calculation: (Weight in lb x 700) (height in inches 2 ) Sample: Find the BMI of a 170 lb male who is 70 inches tall (170 x 700) (70 x 70) (119,000) (4,900) = 24.2 This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 21

22 BMI Values as related to Nutritional Status: BMI < 20 Underweight BMI Normal weight BMI Overweight BMI > 30 Obese Basal Metabolic Rate (BMR) And Resting Energy Expenditure (REE) BMR is a measure of the individual s energy requirements in calories per hour. REE estimates the daily caloric requirements. Usually obtained after 10 hours of fasting. This can be obtained by indirect calorimetry that measures VO 2 and VCO 2, or by using formulas. Listed here is one of the quicker calculations to estimate daily caloric requirements: BMR = IBW (in pounds) x activity factor x illness factor Multiply desired weight or IBW (in pounds) by the activity factor as follows: Activity factors: 12 for sedentary (most patients are in the sedentary range) 15 for moderately active (lots of walking, and moderate exercise for ½ hour or more 3-5 times/week) 18 for vigorously active (lots of daily activity and daily strenuous exercise like jogging). Next, multiply the result by the illness factor as follows: 1.0 for healthy person/no current illness 1.15 for mild illness 1.3 for moderate illness, 1.5 for severe illness, pregnancy or lactation. OXYGEN INDEX (OI) Determining OI is a good clinical tool that can be used to determine the degree of hypoxemia, to monitor for improvement, and as a weaning tool. Good oxygenation OI is 5 or less Some degree of hypoxemia OI is above 5 Severe hypoxemia OI is 20 or greater. OI takes into account the mean airway pressure (Mean Paw), FIO 2, and PaO 2. Since it is common knowledge that it is not good to be on a high FIO 2 and have low PaO 2, the oxygen index formula helps by placing a number on the severity of the hypoxemia. This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 22

23 Formula: Oxygen Index = (Mean P aw x FIO 2 ) PaO 2 Sample #1 Sample #2 Given: Mean P aw 15, FIO 2 1.0, PaO 2 = 60 mmhg Oxygen Index = (15 x 100) = Given: Mean P aw 20, FIO 2 0.4, PaO 2 = 80 mmhg Oxygen Index = (10 x 40) = 5 80 PaO 2 /FiO 2 Ratio (P/F Ratio) The P/F ratio is another tool used to assess the degree of hypoxemia. It can be used for nonintubated patients, since the airway pressure is not included in the calculation. The only factors are the PaO 2 and FIO 2. Normal oxygenation P/F ratio is 200 or Higher Moderate hypoxemia P/F ratio is 100 to 200 Severe hypoxemia P/F ratio is Less than 100 Formula: P/F Ratio = PaO 2 divided by FIO 2 BRIEF REVIEW OF ARTERIAL BLOOD GASES (ABG S) ABG s are generally thought of as a category in itself, while ABG s are classified both as laboratory data and as PFT s. Since ABG interpretation is quite complex, we refer you to the complete course titled ABG Interpretation available at RC Educational Consulting Services, Inc. (RCECS), rcecs.com, or watch for the soon-to-be-released Laboratory Values Applicable to Pulmonary Patient Assessment also at RCECS. Here, we list a table of normal ABG values for reference, and a review of how to quickly interpret ABG s. This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 23

24 Arterial Blood Gases Normal Values Parameter Normal Value Normal Range ph PaCO 2 40 mmhg mmhg PaO mmhg mmhg HCO 3 24 meq/l meq/l BE 0 + or - 2 Hb 14 g/dl g/dl O 2 content 20 vol% vol% SaO 2 98% > 95% COHb 0 < 2% MetHb 0 <2% Interpretation Of Arterial Blood Gases Interpretation ph PaCO 2 HCO 3 Respiratory Acidosis / Ventilatory Failure Acute Chronic/Compensated Acute superimposed or chronic Respiratory Alkalosis / Hyperventilation Acute Chronic/Compensated Metabolic Acidosis Acute Compensated Metabolic Alkalosis Acute Compensated N = Normal N N N N N N N N This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 24

25 NORMAL ACID-BASE BALANCE ACIDOSIS ALKALOSIS Lungs 40 mmhg PaCO 2 [H + ] ph Kidneys 48 Meq/L HCO 3 - Normal This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 25

26 MOST COMMON CAUSES OF ABNORMAL BLOOD GASES Respiratory Acidosis: Insufficient alveolar ventilation. Pulmonary disease, CNS depression, drugs causing respiratory depression. There is a gain in Hydrogen Ion Concentration (PaCO 2 ) without a comparable gain in base (HCO 3 ) resulting in a drop in ph. RESPIRATORY ACIDOSIS ACIDOSIS ALKALOSIS Kidneys 24 Meq/L HCO 3 - ph Lungs 50 mmhg PaCO 2 [H + ] Respiratory Acidosis This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 26

27 Respiratory Alkalosis: Alveolar hyperventilation. Stress, emotional upset, hypoxia, fever, CNS trauma. There is a loss in Hydrogen Ion Concentration (PaCO 2 ) without a related loss in Base (HCO 3 ) which results in a rise in ph. RESPIRATORY ALKALOSIS ACIDOSIS ALKALOSIS Lungs 30 mmhg PaCO 2 [H + ] ph Respiratory Alkalosis Kidneys 24 Meq/L HCO 3 - This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 27

28 Metabolic Acidosis: Lactic acidosis, ketoacidosis (diabetes), renal failure, diarrhea. The decrease in Base (HCO 3 ) is not matched with a loss in Hydrogen Ion Concentration (PaCO 2 ) and therefore, the ph will decrease. METABOLIC ACIDOSIS ACIDOSIS ALKALOSIS Kidneys 15 Meq/L HCO 3 - ph Lungs 40 mmhg PaCO 2 [H + ] Metabolic Acidosis This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 28

29 Metabolic Alkalosis: Hypokalemia (most common cause), high chloride, diuretics, corticosteroids, vomiting, nasogastric tube. Decreases in cations (positive) and/or increases in anion (negative) will increase ph without a parallel increase in Hydrogen Ion Concentration (PaCO 2 ). METABOLIC ALKALOSIS ACIDOSIS ALKALOSIS Lungs 40 mmhg PaCO 2 [H + ] ph Metabolic Alkalosis Kidneys 48 Meq/L HCO 3 - CONCLUSION The use of spirometry in pulmonary function testing has a major role in determining the differential diagnosis of pulmonary and cardiac diseases. It may also be used to rule out a resistive or obstructive process in patients that experience signs and symptoms of lung injury. The results from pulmonary function studies are used to (1) evaluate pulmonary causes of dyspnea, (2) assess severity of the pathophysiologic impairment, (3) follow the course of a particular disease, (4) evaluate the effectiveness of bronchodilator therapy, and (5) assess the patient s preoperative status. Abnormal values require additional testing to assess the lung impairment. Examples of such test include lung volumes, maximum voluntary ventilation, airway resistance, lung compliance, the nitrogen washout gas distribution test, and CO 2 response curve. Specialized test regimens, such as cardiopulmonary stress testing and bronchoprovocation, help assess the severity of lung disorders. This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 29

30 CLINICAL PRACTICE EXERCISE Case #1. The patient is a sixty-two-year-old white male with a fifty-five pack-year smoking history. The patient also worked as a sand blaster for forty years. Recently, he has been complaining of increased shortness of breath. Pre-Bronchodilator Post-Bronchodilator Parameter Actual Predicted % Predicted Actual Predicted % Predicted FVC % % FEV % % FEV 1 % 35% 76% 46% 34% 76% 45% FEF % % PEFR % % SVC % FRC % RV % TLC % Interpretation Case #2. The patient is a thirty-six-year-old black female with a history of systemic lupus erythematosus. Currently, she is complaining of dyspnea and a persistent cough. She has an eighteen pack-year smoking history and no apparent occupational exposure to dust or other noxious materials. She is presently taking prednisone. Pre-Bronchodilator Post-Bronchodilator Parameter Actual Predicted % Predicted Actual Predicted % Predicted FVC % % FEV % % FEV 1 % 78% 78% 100% 83% 78% 106% FEF % % PEFR % % SVC % % FRC % RV % This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 30

31 TLC Interpretation Case # 1 Severe obstructive pattern (all flows decreased, FRC, RV increased), unresponsive to bronchodilator. No restrictive pattern noted. Case # 2 Severe restrictive pattern with a mild obstructive component (all volumes decreased, FEF25-75 decreased), FEF25-75 did not respond to bronchodilator, PEFR did respond suggesting possible reversal of large airway obstruction. This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 31

32 APPENDIX This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 32

33 AARC Clinical Practice Guideline Spirometry, 1996 Update (Reprinted from RESPIRATORY CARE (Respir Care 1996; 41(7): )) S 1.0 PROCEDURE: Spirometry (S): The first American Association for Respiratory Care (AARC) Spirometry Clinical Practice Guideline,(1) published in 1991, was based largely on the American Thoracic Society (ATS) 1987 recommendations. (2) Since that time, the ATS has published new recommendations. (3) This updated AARC Clinical Practice Guideline not only reflects these new ATS recommendations but also contains additional recommendations on the use of bronchodilators in conjunction with spirometry. S 2.0 DESCRIPTION/DEFINITION: The objective of spirometry is to assess ventilatory function. Spirometry includes but is not limited to the measurement of forced vital capacity (FVC), the forced expiratory volume in the first second (FEV1), and other forced expiratory flow measurements such as the FEF25-75%. In addition, it sometimes includes the measurement of maximum voluntary ventilation (MVV). A graphic representation (spirogram) of the maneuver should be a part of the results. Either a volume-time or flow-volume display is acceptable. Other parameters that may be obtained by spirometry include: FEFmax (PEF), FEF75%, FEF50%, FEF25%, FIF50%, and FIFmax (PIF). S 3.0 SETTING: These guidelines should be applied to spirometry performed by trained health-care professionals 3.1 in the pulmonary function or research laboratory; 3.2 at the bedside, in acute, subacute, extended care, and skilled nursing facilities; 3.3 in the clinic, treatment facility, and physician /s office; 3.4 in the workplace or home; 3.5 for public screening. S 4.0 INDICATIONS: The indications for spirometry (4-8) include the need to 4.1 detect the presence or absence of lung dysfunction suggested by history or physical signs and symptoms (eg, age, smoking history, family history of lung disease, cough, dyspnea, wheezing) and/or the presence of other abnormal diagnostic tests (eg, chest radiograph, arterial blood gas analysis); 4.2 quantify the severity of known lung disease; 4.3 assess the change in lung function over time or following administration of or change in therapy; 4.4 assess the potential effects or response to environmental or occupational exposure; 4.5 assess the risk for surgical procedures known to affect lung function; 4.6 assess impairment and/or disability (eg, for rehabilitation, legal reasons, military). This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 33

34 S 5.0 CONTRAINDICATIONS: The requesting physician should be made aware that the circumstances listed in this section could affect the reliability of spirometry measurements. In addition, forced expiratory maneuvers may aggravate these conditions, which may make test postponement necessary until the medical condition(s) resolve(s). Relative contraindications (9,10) to performing spirometry are: 5.1 hemoptysis of unknown origin (forced expiratory maneuver may aggravate the underlying condition); 5.2 pneumothorax; 5.3 unstable cardiovascular status (forced expiratory maneuver may worsen angina or cause changes in blood pressure) or recent myocardial infarction or pulmonary embolus; 5.4 thoracic, abdominal, or cerebral aneurysms (danger of rupture due to increased thoracic pressure); 5.5 recent eye surgery (eg, cataract); 5.6 presence of an acute disease process that might interfere with test performance (eg, nausea, vomiting); 5.7 recent surgery of thorax or abdomen. S 6.0 HAZARD/COMPLICATIONS: Although spirometry is a safe procedure, untoward reactions may occur, and the value of the information anticipated from spirometry should be weighed against potential hazards. The following have been reported anecdotally: 6.1 pneumothorax; 6.2 increased intracranial pressure; 6.3 syncope, dizziness, light-headedness; 6.4 chest pain; 6.5 paroxysmal coughing; 6.6 contraction of nosocomial infections; 6.7 oxygen desaturation due to interruption of oxygen therapy; 6.8 bronchospasm. S 7.0 LIMITATIONS OF METHODOLOGY/ VALIDATION OF RESULTS: 7.1 Spirometry is an effort-dependent test that requires careful instruction and the cooperation of the test subject. Inability to perform acceptable maneuvers may be due to poor subject motivation or failure to understand instructions. Physical impairment and young age (eg, children < 5 years of age) may also limit the subject s ability to perform spirometric maneuvers. These limitations do not preclude attempting spirometry but should be noted and taken into consideration when the results are interpreted. 7.2 The results of spirometry should meet the following criteria for number of trials, acceptability, and reproducibility. The acceptability criteria should be applied before reproducibility is checked Number of trials: A minimum of 3 acceptable FVC maneuvers should be performed. (3) If a subject is unable to perform a single acceptable maneuver after 8 attempts, testing may be discontinued. However, after additional instruction and This material is copyrighted by RC Educational Consulting Services, Inc. Unauthorized duplication is prohibited by law. 34