Pulmonary Function Testing

4 Pulmonary Function Testing


Note 1: This book is written to cover every item listed as testable on the Entry Level Examination (ELE), Written Registry Examination (WRE), and Clinical Simulation Examination (CSE).


The listed code for each item is taken from the National Board for Respiratory Care’s (NBRC) Summary Content Outline for CRT and Written RRT Examinations (http://evolve.elsevier.com/Sills/resptherapist/). For example, if an item is testable on both the ELE and WRE, it is shown simply as (Code: …). If an item is testable only on the ELE, it is shown as (ELE code: …). If an item is testable only on the WRE, it is shown as (WRE code: …).


Following each item’s code, the difficulty level is indicated for the questions on that item on the ELE and WRE. (See the Introduction for a full explanation of the three question difficulty levels.) Recall [R] level questions typically expect the exam taker to recall factual information. Application [Ap] level questions are more difficult, because the exam taker may have to apply factual information to a clinical situation. Analysis [An] level questions are the most challenging, because the exam taker may have to use critical thinking to evaluate patient data to make a clinical decision.


Note 2: A review of the most recent Entry Level Examinations (ELE) has shown that an average of 7 questions out of 140 (or 5% of the exam) covers pulmonary function testing. A review of the most recent Written Registry Examinations (WRE) has shown that an average of 4 questions out of 100 (or 4% of the exam) covers pulmonary function testing. The Clinical Simulation Examination (CSE) is comprehensive and may include everything that should be known by an advanced-level respiratory therapist.



MODULE A











MODULE B





1. Perform bedside spirometry tests





2. Tidal volume






d. Monitor inspiratory/expiratory ratio (WRE code: IA7c) [Difficulty: ELE: R; WRE: Ap]


The I : E ratio is the ratio of the patient’s inspiratory time to the expiratory time. It can be simply measured at the bedside with a stopwatch. Again, make sure the patient is relaxed and breathing in the normal pattern to get an accurate timing. Measure several of the patient’s inspiratory times and expiratory times to figure an average for each. A spirometer that gives a printout is needed if a more complete analysis of the patient’s breathing pattern is necessary.


A normal, spontaneously breathing patient has an I : E ratio of 1 : 2 to 1 : 4. A prolonged inspiratory time often is seen in patients with an upper airway obstruction. A prolonged expiratory time often is seen in patients with asthma or chronic obstructive pulmonary disease (COPD). Any abnormal I : E ratio should be investigated. For example, patients with Kussmaul’s respiration, Cheyne-Stokes respiration, or Biot’s respiration will have unusual I : E ratios.






4. Alveolar ventilation





5. Maximum inspiratory pressure



a. Perform the procedure (Code: IB79n [Difficulty: ELE: R, Ap; WRE: An]


The maximum inspiratory pressure (MIP) is the greatest amount of negative pressure the patient can create when inspiring against an occluded airway. It also is known as negative inspiratory force (NIF). The following factors affect the test results: strength of the diaphragm and accessory muscles of inspiration, lung volume when the airway is occluded, ventilatory drive, and the length of time the airway is occluded. MIP is most commonly used to determine the weanability of mechanically ventilated patients. In addition, it is used to help monitor the strength of patients with a neuromuscular disease.


A study of the literature reveals that a number of measurement devices have been assembled and that different bedside techniques have been used to determine the effort of a patient breathing naturally, an intubated patient, and a patient breathing with assistance from a mechanical ventilator. Branson and colleagues (1989) and Kacmarek and colleagues (1989) make a strong case for the use of a double one-way valve to connect the intubated patient to the manometer (Figure 4-2). Use of the one-way valve lets the patient exhale but prevents an inhalation when the practitioner occludes the opening. This forces the patient to inhale from closer to residual volume with each breathing effort. These researchers also recommend that the patient make inspiratory efforts for 15 to 20 seconds.



Steps in the MIP procedure for a normally breathing patient include the following:














6. Maximum expiratory pressure



a. Perform the procedure (Code: IB9n) [Difficulty: ELE: R, Ap; WRE: An]


The maximum expiratory pressure (MEP) is the greatest amount of positive pressure the patient can create when expiring from total lung capacity (TLC) against an occluded airway. It also is known as a maximum expiratory force (MEF). The following factors affect the test results: patient cooperation and effort, strength of the expiratory muscles, lung volume when the airway is occluded, ventilatory drive, and the length of time the airway is occluded. The MEP is used to determine the weanability of mechanically ventilated patients and to monitor the strength of patients with a neuromuscular disease.


As with the MIP test, a study of the literature reveals that a number of measurement devices have been assembled and that different bedside techniques have been used to determine the effort of a patient breathing naturally and the effort of one who is intubated and breathing by way of a mechanical ventilator. A strong case can be made for the use of a double one-way valve to connect the intubated patient to the manometer (see Figure 4-2). Use of the one-way valves lets the patient inhale but prevents an exhalation when the practitioner occludes the expiratory opening. This forces the patient to exhale from closer to TLC with each breathing effort. However, the expiratory efforts should not be held for longer than 3 seconds. This test is similar to the Valsalva maneuver and can cause a reduction in cardiac output because of the high intrathoracic pressure.


Steps in the MEP procedure for a normally breathing patient include the following:











It is important to monitor any patient for signs of undue stress and hypoxemia, such as tachycardia, bradycardia, ventricular dysrhythmias, hypotension, and decreasing saturation on pulse oximetry. If any of these is seen, the procedure should be stopped and the patient reoxygenated and ventilated.




7. Vital capacity




b. Interpret the results (Code: IB10d) [Difficulty: ELE: R, Ap; WRE: An]


See Figure 4-1 for a graphic tracing of a nonforced VC. Compare it with the tracing on Figure 4-3, which shows a forced vital capacity (FVC). In a patient without obstructive lung disease, the same volume should be found in a nonforced VC and an FVC. A patient with asthma or chronic obstructive lung disease may have a smaller FVC than nonforced VC because of small airway collapse during the maximum effort. The following discussion on the FVC includes predicted values for male and female patients and guidelines on the interpretation.






9. Peak flow




b. Interpret the results (Code: IB10e) [Difficulty: ELE: R, Ap; WRE: An]


The peak flow and FEV1 are the bedside measurements most commonly used to evaluate the response of a patient with asthma or COPD to inhaled bronchodilator medications. If the medication dose is effective, the patient’s peak flow will increase significantly from the premedication value. Many peak flowmeters come with adjustable markers for the National Asthma Education Program’s “color zone” scheme:





Current asthma guidelines state that if an asthma patient’s peak flow is in the green zone, the medications are adequately controlling the asthma. If the peak flow is in the yellow zone, the patient’s medications are not adequately controlling the asthma. Increased doses are indicated if ordered by the physician. If the peak flow is in the red zone, the patient’s medications are not adequately controlling the asthma. The patient needs more bronchodilator medication. The home care patient should get medical help as soon as possible. Each patient should have his or her individually calculated color zones marked on the peak flowmeter to guide medication usage. The patient should be instructed on the meaning of the zones and the proper use of medications. See Module C for more discussion of the peak flow.



MODULE C






2. Exhaled nitric oxide





3. Forced vital capacity



a. Perform the test (Code: IB9e and IIIE7a) [Difficulty: ELE: R, Ap; WRE: An]


The FVC is the greatest volume of gas that the patient can exhale as rapidly as possible after the lungs have been completely filled. Normally, the FVC is the same volume as that found in a slow or nonforced VC. Careful instructions, demonstrations, and coaching are needed to ensure that the patient’s efforts are the best possible. At least three proper efforts must be obtained.


If the measurement instrument does not give a printout, simply record the patient’s efforts in the chart. If the measurement instrument does give a printout, include copies of the efforts. See Figure 4-3 for the tracing of a properly performed FVC. The tracing allows comparison of the volumes exhaled in a series of 1-second intervals. Because of this, the tracing often is referred to as a volume-time curve. Note that the start of the effort is smooth and without interruption. The initial fast flow of gas from the upper airway is seen as the nearly vertical part of the tracing. The rest of the tracing is smooth without any coughing or other interruptions in the patient’s effort. The tracing becomes progressively more horizontal as the end of the effort is reached. Encourage the patient to try to push out as much air as possible as the end approaches. To provide an acceptable FVC, the patient must show maximum effort without coughing or closing the glottis, and the expiratory effort must last at least 6 seconds. The patient’s final 2 seconds of expiratory effort should show no appreciable airflow. Each of the three acceptable FVCs must show these traits and close similarity of the patient’s efforts.



b. Interpret FVC and spirometry graphics


Figure 4-3 was made on a chain-compensated, water-seal spirometry system. Note how the tracing progresses from the right to the left. The Stead-Wells system shows the same tracing “upside down” compared with the chain-compensated system. The tracing starts on the left and moves to the right (Figures 4-4 and 4-5). Other tracings may show either the chain-compensated or the Stead-Wells tracings in a mirror image or opposite shape.







c. Interpret the results (Code: IB10e and IIIE7a) [Difficulty: ELE: R, Ap; WRE: An]


Normal racial differences in the FVC must be taken into consideration. Most modern pulmonary function systems automatically adjust the measured values for racial differences when so programmed by the operator. If not, the predicted values should be mathematically adjusted by the therapist. The predicted normal values, in liters, for the FVC in Caucasian patients were reported by Morris, Koski, and Johnson (1971) as:*



image





African Americans are known to have a smaller lung capacity than Caucasians of the same height. For this reason, a 10% to 15% adjustment should be made for the predicted FVC and TLC of an African American patient. In other words, the predicted values for this patient are 85% to 90% of those of a comparable Caucasian patient.


Adjustments for Hispanic and Asian populations are not so well documented. It has been reported that the predicted FVC values should be adjusted downward by 20% to 25% for Asians.


It has been commonly accepted that a measured FVC at least 80% of the predicted FVC is considered to be within normal limits for adults of all races. In addition, the FEV1 and TLC measurements have been included in this 80% of predicted rule. More recent studies by Knudson, Kaltenborn, Knudson, and associates (1987) and Paoletti, Viegi, Pistelli, and associates (1985) suggest that normal values for most tests should be determined by finding the percentage of predicted value above which 95% of the population would be seen (the so-called normal 95th percentile). Even though this method finds 5% (1 in 20) of healthy nonsmokers to be abnormal, it offers more realistic predicted values. It is normal to see a decline in the FVC with age.


Restrictive problems, such as advanced pregnancy, obesity, ascites, neuromuscular disease, sarcoidosis, and chest wall or spinal deformity, can result in a small FVC. Patients with chronic obstructive lung diseases, such as emphysema, bronchitis, asthma, cystic fibrosis, and bronchiectasis, commonly have a small FVC. (Figure 4-5 shows a comparison of the spirometry tracings of a normal, an obstructed, and a restricted patient.)


The limitations of this text prevent a discussion of back-extrapolation to find the start of a less than perfect effort or the calculations for correcting volumes and flows from atmospheric temperature, pressure, saturated (ATPS) to body temperature, pressure, saturated (BTPS). However, most textbooks on pulmonary function testing discuss these topics. Because the BTPS correction reflects the patient’s true effort, it is standard practice to report all flows and volumes in BTPS.





4. Peak flow




b. Interpret the results (Code: IB10d) [Difficulty: ELE: R, Ap; WRE: An]


The PF is directly related to height and indirectly related to age. Therefore, the taller the patient, the greater the PF. The PF decreases with age. The PF is a rather nonspecific measurement of airway obstruction. It measures flow through the upper airways and is reduced in patients with an upper airway problem, such as a tumor, vocal cord paralysis, or laryngeal edema.


The PF test is most often given to patients having an asthma attack as a quick and easy measurement of small airway obstruction. Current asthma guidelines state that if the peak flow of a patient with asthma is 80% to 100% of predicted or personal best, he or she is in the green zone. This means that the patient’s medications are adequately controlling the asthma. If the peak flow is 50% to 79% of predicted or personal best, he or she is in the yellow zone. This means that the patient’s medications are not adequately controlling the asthma. Increased doses are indicated if ordered by the physician. If the peak flow is less than 50% of predicted or personal best, the patient is in the red zone. This means that the patient’s medications are not adequately controlling the asthma. The patient should get medical help as soon as possible.


It is the respiratory therapist’s responsibility to calculate the patient’s color zones and mark them on the patient’s personal peak flowmeter. The therapist must instruct the patient in the meaning of the color zones and the appropriate use of the prescribed inhaled bronchodilator and/or corticosteroid medications.



Timed forced expiratory volume tests


All of the timed forced expiratory volume tests are derived from a properly performed FVC test (see Figure 4-3). When the FVC is done correctly, the following values can be properly calculated and evaluated to determine the patient’s condition. As discussed earlier, an FVC within 80% of predicted is interpreted as within normal limits. Therefore, if the results of the following tests show patient values within 80% of predicted, the results are interpreted as being within normal limits.



5. Forced expiratory flow25%-75% (FEF25%-75%)





6. Forced expiratory volume timed (FEVT)



a. Perform the procedure (Code: IB9u) [Difficulty: ELE: R, Ap; WRE: An]


The FEVT is the volume of air exhaled from an acceptable FVC in the specified time. The time increments are 0.5, 1, 2, and 3 seconds or more and are listed as FEV0.5, FEV1, FEV2, FEV3, and so on. It is important that the FVC have a good start and a maximum effort to the end.


The FEV1 is the measurement most commonly used, along with the FVC, to judge the patient’s response to inhaled bronchodilators, for bronchoprovocation testing to screen for asthmatic tendencies, to detect exercise-induced asthma, and for simple screening. BTPS correct all the measured values.


The timed forced expiratory volumes (FEV0.5, FEV1, FEV2, FEV3) effectively “cut” the FVC into sections based on how much volume the patient forcibly exhales in 0.5, 1, 2, and 3 seconds. Some patients with severe obstructive lung disease require several more seconds to exhale completely. In these cases, simply keep measuring the volume exhaled in each additional second. Figure 4-7 shows an FVC tracing that is subdivided at 0.5-, 1-, 2-, and 3-second intervals. Some bedside units give a numeric value for some or all of the timed intervals; however, it is best to have a spirometer that produces a printed copy of the patient’s FVC effort. The individual volumes can be determined by marking the vertical distance on the volume scale from the baseline (total lung capacity) to the respective arrow tips.





7. Forced expiratory volume/forced vital capacity ratio (FEVT/FVC or FEVT%)




Jun 18, 2016 | Posted by in RESPIRATORY | Comments Off on Pulmonary Function Testing

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