ATS Pulmonary Function Laboratory Manual

ATS Pulmonary Function Laboratory Management & Procedure Manual | 3rd Edition

Test Procedure for FRC pleth

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Step Action 2. Instruct the patient to attach to the mouthpiece and breathe quietly until a stable end-expiratory level is achieved (usually 3 to 10 breaths). 3. When the patient is at or near FRC, close the shutter at end-expiration for approximately 2 to 3 seconds, and instruct the patient to perform a series of gentle pants (approximately ± 10 cm H 2 O or 1 kPa) at a fre- quency between 0.5 and 1.0 Hertz. Panting frequencies greater than 1.5 Hertz may lead to errors, and less than 0.5 Hertz may cause problems with the controlled leak of the body plethysmograph (7). 4. A series of 3 to 5 technically satisfactory panting maneuvers should be recorded (i.e., on the pressure/volume plot a series of almost superimposed straight lines within the calibrated pressure range of the transducers separated by only a small thermal drift), after which the shutter is opened and the patient performs and ERV maneuver followed by a slow IVC maneuver (or as a second priority an IC maneuver followed by a slow expiratory VC maneuver). If needed, the patient can come off the mouthpiece and rest between TGV/VC maneuvers. Patients with severe dsypnea may have difficulty performing the preferred VC method (i.e., ERV immediately after TGV followed by a slow IVC). To overcome this, the patient can be instructed to take 2 or 3 tidal breaths after the panting maneuver prior to performing the linked ERV and IVC maneuvers. 5. Obtain at least three separate, acceptable trials (FRC pleth values) that agree within 5% (i.e., the difference between the highest and lowest value divided by the mean is 0.05 or less), and report the mean value. If there is a larger deviation, obtain additional values until 3 values agree within 5% of their mean, and report the mean. The FRC pleth value is rounded to two decimal places (e.g., 4.53 L). Set-up and test preparation: • Turn equipment on, allow adequate warm-up time, and calibrate as instructed by the manufacturer. • Ask the patient if he/she has a perforated eardrum (if so, use an earplug). • Seat the patient comfortably; dentures need not be removed. Explain the procedure emphasizing the need to avoid leaks around the mouthpiece during the washout, and place the nose clip on the patient’s nose. 2. Have the patient breathe on the mouthpiece for approximately 30–60 seconds to become accustomed to the apparatus, and to assure a stable end-tidal expiratory level. For young children, testing is best if done while the child watches a video and sits upright in the lap of the parent or someone the child trusts. For very young children, a small face mask that can be sealed with putty is preferred (8). 3. When breathing is stable and consistent with the end-tidal volume being at FRC, switch the patient into the circuit so 100% O 2 is inspired instead of room air. 4. Monitor the N 2 concentrations during the washout. A change in inspired N 2 > 1% or a sudden large increase in expiratory N 2 concentrations indicate a leak and the test should be stopped and repeated after a 15-minute period of breathing room air. Commercial software typically will display % N 2 (or log % N 2 ) plotted against volume or number of breaths. 5. Testing should be continued until N 2 concentration falls below 1.5% for at least three successive breaths. (continues on next page) Test Procedure for FRC N2 Step Action 1.

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