AARC GUIDELINE: CARBON MONOXIDE DIFFUSING CAPACITY, 1999 UPDATE (replaces update published in January, 1999) AARC Clinical Practice Guideline Single-Breath Carbon Monoxide Diffusing Capacity, 1999 Update DLCO 1.0 PROCEDURE DLCOsb is measured is also commonly report- Single-breath diffusing capacity for carbon monox- ed; the units for the VA are liters at body tem- ide (DLCOsb), sometimes referred to as the transfer perature and pressure, saturated with water factor for carbon monoxide (TCO). vapor (BTPS). 2.3 The ratio of DLCO to VA is also commonly DLCO 2.0 DESCRIPTION/DEFINITION reported as the DL/VA or simply D/VA. The first American Association for Respiratory Care (AARC) single-breath diffusing capacity (DL- DLCO 3.0 SETTINGS: COsb) Clinical Practice Guideline (CPG) was pub- 3.1 Pulmonary function laboratories lished in 1993, and was based largely on the Ameri- 3.2 Cardiopulmonary laboratories can Thoracic Society (ATS) 1987 recommenda- 3.3 Clinics tions.1 Since that time, the ATS has published new 3.4 Physicians’ offices recommendations.2 This updated AARC CPG re- flects the 1995 ATS recommendations. Various DLCO 4.0 INDICATIONS: methods are commercially available to perform Tests of diffusing capacity may be indicated for DLCOsb. This Guideline can be applied in many (Specific conditions and direction of change in (perhaps most) cases and is based on experience DLCO are shown in the Appendix.): and research with the traditional method (10-sec- 4.1 evaluation and follow-up of parenchymal ond breathhold with alveolar sample collection). lung diseases including: idiopathic pulmonary For non-traditional or newer methods, it is the man- fibrosis (IPF, also known as usual interstitial ufacturer’s and the scientific community’s responsi- pneumonitis, or UIP) and bronchiolitis obliter- bility to define the comparability of the newer ans organizing pneumonia (BOOP, or crypto- methods with the old. genic organizing pneumonia, COP), diseases associated with dusts such as asbestos, or drug Diffusing capacity is a measurement of carbon reactions (eg,from amiodarone) or related to monoxide (CO) transfer from inspired gas to pul- sarcoidosis;1-3 and for quantification of disabili- monary capillary blood. During the test, the subject ty associated with interstitial lung disease; 4 inspires a gas containing CO and oneRETIRED or more tracer 4.2 evaluation and follow-up of emphysema gases to allow determination of the gas exchanging and cystic fibrosis;5,6 and differentiating among capability of the lungs. Although several different chronic bronchitis, emphysema, and asthma in methods of measuring DLCO have been described, patients with obstructive patterns; and for quan- the most commonly used technique is the single- tification of impairment and disability. breath maneuver, or DLCOsb. For purposes of this 4.3 evaluation of cardiovascular diseases (eg, guideline, recommendations associated with the primary pulmonary hypertension, acute or re- 2 DLCOsb are referenced. Many of these standards current thromboembolism, or pulmonary apply indirectly to other methods of measuring dif- edema);7,8 fusing capacity. 4.4 evaluation of pulmonary involvement in 2.1 DLCO is usually expressed in mL CO min-1 systemic diseases (eg, rheumatoid arthritis, sys- . torr-1 at standard temperature and pressure dry temic lupus erythematosus);9-11 (STPD). 4.5 evaluation of the effects of chemotherapy 2.2 The alveolar volume (VA) at which the agents or other drugs (eg, amiodarone, RESPIRATORY CARE • MAY 1999 VOL 44 NO 5 539 AARC GUIDELINE: CARBON MONOXIDE DIFFUSING CAPACITY, 1999 UPDATE bleomycin) known to induce pulmonary dys- DLCO 7.0 LIMITATIONS OF METHODOLO- function;12-14 GY/VALIDATION OF RESULTS: 4.6 evaluation of pulmonary hemorrhage;15 7.1 Limitations of the common methods used 4.7 as an early indication of certain pulmonary for DLCO include: infections (eg, pneumocystis pneumonia);16 7.1.1 DLCO should be corrected for 4.8 prediction of arterial desaturation during hemoglobin (Hb) level according to the exercise in some patients with lung disease.17,18 method described by Cotes and co-work- ers.20 DLCO 5.0 CONTRAINDICATIONS 7.1.1.1 For adolescent boys(≥ 15 years 5.1 Absolute contraindications to performing a of age) and adult men, the Hb is adjust- diffusing capacity test are ed to a value of 14.6 g/dL: 5.1.1 the presence of carbon monoxide Hb-adjusted DLCO = observed DLCO (10.22 + toxicity Hb)/1.7 Hb. 5.1.2 dangerous levels of oxyhemoglobin 7.1.1.2 For children < 15 years of age desaturation without supplemental oxygen. and women the Hb is adjusted to a 5.2 Relative contraindications to performing a value of 13.4 g/dL: diffusing capacity test are Hb-adjusted DLCO = observed DLCO (9.38 + 5.2.1 mental confusion or muscular in- Hb)/1.7 Hb. coordination preventing the subject from 7.1.2 For purposes of interpretation, adequately performing the maneuver or DLCO should be corrected for the effects inability to obtain or maintain an ade- of COHb present in the subject’s blood.1 quate lip seal on the instrument mouth- COHb-adjusted DLCO = measured piece; DLCO (1+ [%COHb/100]). 5.2.2 a large meal or vigorous exercise 7.1.3 DLCO increases with increasing al- immediately before the test;1 titude and appropriate correction for the 5.2.3 smoking within 24 hours of test ad- alveolar or inspired oxygen pressures are ministration (smoking may have a direct recommended.1 effect on DLCO independent of the effect Altitude-adjusted DLCO = measured 19 of COHb ); DLCO (1.0 + 0.0035(PAO2 - 120]) 5.2.4 decreased lung volumes that would or not yield valid test results; Altitude-adjusted DLCO = measured 5.2.5 devices that are improperly calibrat- DLCO (1.0 + 0.0031(PIO2 - 150]) ed or maintained or the unavailability of a (where estimated PIO2 = 0.21 [PB - 47 qualified operator. torr].) 7.1.4 A 4-minute minimum interval DLCO 6.0 HAZARDS/COMPLICATIONS: should elapse between subsequent ma- 6.1 DLCO requires breathholdingRETIRED at total lung neuvers to allow test gas to be eliminated sb capacity (TLC); some patients may perform ei- from the lungs.1 ther a Valsalva (higher than normal intratho- 7.1.5 DLCO varies with body position; racic pressure) or Müller (lower than normal in- the upright seated position is recommend- trathoracic pressure) maneuver. Either of these ed. can result in alteration of venous return to the 7.1.6 Abnormal breathholding maneuvers heart and pulmonary capillary blood volume. (Valsalva or Müller) alter DLCO.21 6.2 Interruption of supplemental oxygen may 7.1.7 Other factors that may alter measure- result in oxyhemoglobin desaturation. ment of DLCO include recent alcohol con- 6.3 Transmission of infection is possible via sumption,22 vigorous exercise, smoking, improperly cleaned mouthpieces or as a conse- diurnal variation, and bronchodilators.23 quence of the inadvertent spread of droplet nu- 7.1.8 Pregnancy (first trimester only) has clei or body fluids (patient-to-patient or patient- been reported to be associated with an in- to-technologist). crease in DLCO.24 Menstruation may also 540 RESPIRATORY CARE • MAY 1999 VOL 44 NO 5 AARC GUIDELINE: CARBON MONOXIDE DIFFUSING CAPACITY, 1999 UPDATE influence DLCO.25 valve and circuit (if a compressed gas 7.1.9 Breathhold time should be calculat- source is used). 2 ed using the method of Jones-Meade. 7.4.7 Chemical absorbers (for CO2 and Other methods may produce significantly H2O) or selectively permeably tubing different results. should be replaced at the frequency rec- 7.2 Large interlaboratory differences in mea- ommended by the manufacturer, when sured DLCO and in percent-of-predicted saturated (as indicated by color change) or DLCO have been observed 26,27 and are attribut- sooner. In addition, the chemical ab- ed to variations in testing techniques and com- sorbers should be placed in the proper putational algorithms and errors in gas analysis. order (ie, CO2 absorber should precede The choice of equipment may also influence H2O absorber), should be replaced when the measured DLCO.27,28 exhausted, and should be arranged ac- 7.3 Choice of reference equations may affect the cording to how alveolar gas is analyzed. final interpretation of measured DLCO values.29 7.4.8 Normal standard subjects (biologic 7.4 Validation of the testing technique and controls) may be used to establish intra- equipment may include but is not limited to subject coefficient of variation and to 7.4.1 Volume accuracy of spirometer serve as a quality control population.2 should be < ± 3% over an 8-L volume (ie, meets or exceeds all ATS recommenda- DLCO 8.0 ASSESSMENT OF NEED (see Sec- tions2) and must be checked each day that tion 4.0 Indications) the test is performed, using a 3.00 L (min- imum) syringe. Spirometer must maintain DLCO 9.0 ASSESSMENT OF TEST QUALITY: accuracy with varying gas concentrations . Individual test maneuvers and results should be 7.4.2 Gas analyzers should be subjected to evaluated according to the ATS recommendations.2 a 2-point calibration before each test. 9.1 Use of proper quality-controlled equipment. Manufacturers should be encouraged to 9.2 Provision of test instructions before testing provide software and techniques by which commences and determination that the subject analyzer linearity may be easily checked is able to follow commands. (eg, dilution technique). Gas analyzer lin- 9.3 Inspiratory volume exceeding 90% of the earity should be largest previously measured vital capacity 7.4.2.1 within ± 1%, from zero to (FVC or VC), attained in < 2.5 s in healthy sub- full span, of maximal value over the jects and within 4 s in patients with moderate to duration of the test, severe airway obstruction.