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Static Lung Volumes: 2001 Revision & Update

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Static Lung Volumes: 2001 Revision & Update AARC GUIDELINE: STATIC LUNG VOLUMES: 2001 REVISION & UPDATE AARC Clinical Practice Guideline Static Lung Volumes: 2001 Revision & Update SLV 1.0 PROCEDURE: When TV is reported, an average of at least 6 Measurement of static lung volumes and capacities breaths should be used.2 (Fig. 1) in adults and in children (age ≥ 5). This guideline 2.3 Inspiratory reserve volume (IRV) is the focuses on commonly used techniques for measur- maximal volume of air that can be inhaled from ing lung volumes, including spirometry, gas-dilu- TV end-inspiratory level.2 tion determination of functional residual capacity 2.4 Expiratory reserve volume (ERV) is the (FRC), and whole-body plethysmography determi- maximal volume of air that can be exhaled after nation of thoracic gas volume (VTG). Other meth- a normal tidal exhalation (ie, from functional ods (eg, single-breath nitrogen, single-breath heli- residual capacity, or FRC).2 um, and roentgenologic determinations of lung vol- 2.5 Residual volume (RV) is the volume of gas umes) are not discussed in this document, but may remaining in the lung at the end of a maximal be useful in certain situations. expiration.1 It may be calculated by subtracting ERV from FRC (RV = FRC – ERV) or by sub- SLV 2.0 DESCRIPTION/DEFINITIONS: tracting vital capacity (VC) from total lung ca- 2.1 Static lung volumes are determined using pacity, or TLC (RV = TLC – VC). methods in which airflow velocity does not 2.6 Inspiratory capacity (IC) is the maximal play a role. The sum of two or more lung-vol- volume of air that can be inhaled from the tidal- ume subdivisions constitutes a lung capacity. volume end-expiratory level (ie, FRC). It is The subdivisions and capacities are expressed equal to the sum of TV and IRV.2 in liters at body temperature and pressure satu- 2.7 Vital capacity (VC) is the volume change rated with water vapor (BTPS). that occurs between maximal inspiration and maximal expiration. The subdivisions of the Maximal Inspiration VC include TV, inspiratory reserve volume (IRV), and expiratory reserve volume (ERV). IC IRV The largest of three technically satisfactory VC End Inspiration maneuvers should be reported. The two largest VC TV VCs should agree within 5% or 100 mL, TLC RETIREDwhichever is larger. The volume change can be End Expiration accomplished in several ways.2 ERV FRC 2.7.1 Two-stage VC: a slow maximal inspira- Maximal Expiration tion from TV end-expiratory level after a nor- RV mal exhaled TV, followed by quiet breathing, followed by a slow maximal expiration from Fig. 1. Subdivisions of Lung Volume TV (ie, end-expiratory level, or functional residual capacity (ie, FRC). The reverse ma- 2.2 Tidal volume is the volume of air that is in- neuver is also acceptable; haled or exhaled with each respiratory cycle.1 2.7.2 Forced vital capacity (FVC): the volume of (Although both VT and TV have been used to air exhaled during a forced maximal expiration denote this volume, TV is used in this guide- following a forced maximal inspiration. The line.) It varies with the conditions under which FIVC is the forced VC obtained during a maxi- it is measured (eg, rest, exercise, posture). mal inspiration following a maximal expiration. RESPIRATORY CARE • MAY 2001 VOL 46 NO 5 531 AARC GUIDELINE: STATIC LUNG VOLUMES: 2001 REVISION & UPDATE 2.8 FRC is the volume of air in the lung at the exist; the relative contraindications for spirom- average TV end-expiratory level. It is the sum etry are appropriate and may include:2,6,7 of the ERV and RV. When subdivisions of lung 5.1.1 hemoptysis of unknown origin; volume are reported, the method of measure- 5.1.2 untreated pneumothorax; ment should be specified (eg, helium dilution, 5.1.3 pneumothorax treated with a chest nitrogen washout, body plethysmography).2 tube—because the chest tube may intro- 2.9 Thoracic gas volume (VTG) is the volume of duce leaks and interfere with gas-dilution air in the thorax at any point in time and at any measurements; level of thoracic expansion. It is usually mea- 5.1.4 unstable cardiovascular status; sured by whole-body plethysmography. It may 5.1.5 thoracic and abdominal or cerebral be determined at any level of lung inflation; aneurysms. however, it is most commonly determined at or 5.2 With respect to whole-body plethysmogra- near FRC.2 As an alternative, lung volume may phy, such factors as claustrophobia, upper body be tracked continuously, and FRC determined paralysis, obtrusive body casts, intravenous from VTG by addition or subtraction of volume. (I.V.) pumps, or other conditions that immobi- 2.10 Total lung capacity (TLC) is the volume of lize or prevent the patient from fitting into or air in the lung at the end of a maximal inspira- gaining access to the ‘body box’ are a concern. tion. It is usually calculated in one of two ways: In addition, the procedure may necessitate stop- (1) TLC = RV + VC or (2) TLC = FRC + IC. ping I.V. therapy or supplemental oxygen. The method of measurement (eg, gas dilution, body plethysmography) should be specified.2 SLV 6.0 HAZARDS/COMPLICATIONS: 6.1 Infection may be contracted from improper- SLV 3.0 SETTINGS: ly cleaned tubing, mouthpieces, manifolds, 3.1 Pulmonary function laboratories valves, and pneumotachometers. 3.2 Cardiopulmonary laboratories 6.2 Hypoxemia may result from interruption of 3.3 Clinics and physicians’ offices O2 therapy in the body box. 3.4 Patient care areas 6.3 Ventilatory drive may be depressed in sus- 3.5 Study and field settings ceptible subjects (ie, some CO2 retainers) as a consequence of breathing 100% oxygen during SLV 4.0 INDICATIONS: the nitrogen washout.8 Such patients should be Indications include but are not limited to the need carefully observed. 4.1 to diagnose restrictive disease patterns;3 6.4 Hypercapnia and/or hypoxemia may occur 4.2 to differentiate between obstructive and re- during helium-dilution FRC determinations as strictive disease patterns,2 particularly in the a consequence of failure to adequately remove 4 presence of a reduced VC; CO2 or add O2 to the rebreathed gas. 4.3 to assess response to therapeutic interven- tions (eg, drugs, transplantation,RETIRED radiation, SLV 7.0 LIMITATIONS OF METHODOLOGY/ chemotherapy, lobectomy, lung-volume-reduc- VALIDATION OF RESULTS: tion surgery); 7.1 Patient-related limitations: 4. 4 to aid in the interpretation of other lung 7.1.1 Slow VC is effort-dependent and re- 2 function tests (eg, DL/VA, sGaw, RV/TLC; quires understanding and motivation on 4. 5 to make preoperative assessments2 in pa- the subject’s part. Physical and/or mental tients with compromised lung function (known impairment may limit patient’s ability to or suspected) when the surgical procedure is perform. known to affect lung function; 7.1.2 Some patients may be unable to per- 4. 6 to provide an index of gas trapping (by form the necessary panting maneuver re- comparison of gas dilution techniques with quired for plethysmographic determina- plethysmographic measurements).5 tion of FRC. SLV 5.0 CONTRAINDICATIONS: 7.1.3 Some subjects are unable to maintain 5.1 No apparent absolute contraindications mouth seal or cooperate adequately for the 532 RESPIRATORY CARE • MAY 2001 VOL 46 NO 5 AARC GUIDELINE: STATIC LUNG VOLUMES: 2001 REVISION & UPDATE time necessary to perform the test. Cough 7.2.2.2 Closed-circuit multibreath heli- is a common cause of such limitations. um equilibration method 7.1.4 Certain pathologic conditions in the 7.2.2.2.1 The helium concentration subject can cause a leak in a lung-volume- should be measured at least every 15 measurement system (eg, perforated seconds, and water vapor should be eardrum, tracheostomy, transtracheal removed from the fraction of gas catheter, chest tube). that is introduced into the helium an- 7.1.5 FRC measured by gas dilution may alyzer.2 The reference cell of the He be underestimated in individuals with air- katharometer should also have a flow limitation and air trapping.9,10 Body water absorber in-line, if room air is plethysmography may overestimate FRC used for zeroing. in subjects with severe airway obstruction 7.2.2.2.2 A mixing fan should circu- or induced bronchospasm at panting fre- late and completely mix the air quencies greater than 1 Hz (1 cycle/sec- throughout the main circuit. ond).11-13 7.2.2.2.3 The breathing valve and 7.1.6 Elimination of nitrogen from tissues mouthpiece (without a filter) should and blood can result in overestimation of add < 60 mL dead space to the sys- the FRC in healthy subjects unless appro- tem for adults and a proportionately priate corrections are made.2 reduced increase for pediatric sub- 7.2 Test validation encompasses those calibra- jects and should be easy to disas- tion and procedural elements that help assure semble for cleaning. credible results: 7.2.2.2.4 Gas mixing is considered 7.2.1 Spirometry complete when the change in helium 7.2.1.1 Spirometers (volume-displace- concentration has been constant ment devices or flow-sensing devices) over a 2-minute period (ie, changes should meet the American (1994) and less than 0.02%) or 10 minutes has European Thoracic Societies’ (1993) elapsed.4 If the helium concentration current accepted standards.2,3 Volume- can be read directly or processed by displacement spirometers should be computer, helium equilibration can leak tested when calibrated (eg, be assumed when the change is < daily).14 0.02% in 30 seconds.2 7.2.1.2 The VC should be measured as 7.2.2.2.5 The need to correct for body close as possible in time to the FRC de- absorption of helium is controversial.
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