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Editorial |

Low Pulse Oximetry Reading: Time for Action or Reflection? FREE TO VIEW

Andrew R. Tomlinson, MD; Benjamin D. Levine, MD; Tony G. Babb, PhD
Author and Funding Information

FINANCIAL/NONFINANCIAL DISCLOSURES: None declared.

aDivision of Pulmonary and Critical Care Medicine, University of Texas Southwestern Medical Center, Dallas, TX

bDivision of Cardiology, University of Texas Southwestern Medical Center, Dallas, TX

cInstitute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital, Dallas, TX

CORRESPONDENCE TO: Andrew Tomlinson, MD, Division of Pulmonary and Critical Care Medicine, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75390


Copyright 2016, American College of Chest Physicians. All Rights Reserved.


Chest. 2017;151(4):735-736. doi:10.1016/j.chest.2016.11.001
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Published online

When a fact appears to be opposed to a long train of deductions, it invariably proves to be capable of bearing some other interpretation.Sherlock Holmes, in A Study in Scarlet

Pulse oximetry allows a rapid noninvasive estimate of arterial oxygen saturation. Since its development in the 1970s, it has made a significant impact, particularly in the fields of perioperative and intensive care medicine. Most modern pulse oximeters determine arterial hemoglobin saturation through the use of two light-emitting diodes in the red (660 nm) and infrared (940 nm) spectrum. The differential absorption of these two wavelengths of light by oxygenated and deoxygenated hemoglobin during pulsatile blood flow allows for accurate estimation of arterial oxygen saturation under most conditions. However, pulse oximeters can give erroneous from a variety of causes, including hypoperfusion, dyshemoglobins (including carboxyhemoglobin), nail polish, darker skin pigmentation, venous pulsations, and, perhaps most frequently, motion artifact. Clinicians must consider these possible causes of error when interpreting pulse oximetry results, especially those that are not consistent with a patient’s clinical status and medical history. Clinically significant desaturations in an ambulatory setting are uncommon in patients without significant pathologic pulmonary conditions or pulmonary vascular disease.

The potential of erroneous readings must be considered, especially measurements made during exercise. Continuous pulse oximetry is commonly combined with a 6-min walk test (6MWT) in the ambulatory setting when evaluating dyspnea. Prior American Thoracic Society guidelines for the 6MWT recommend against continuous monitoring of oxygen saturation during a 6MWT because of concerns about erroneous readings. Prior studies have shown significant inaccuracies in this setting, likely due to motion artifact., In addition, many handheld pulse oximeters available in the office setting do not display oximetry waveforms or alternative evaluations of measurement quality. This leads to a greater risk of misinterpretation, as a digital readout is assumed to be accurate without a proper understanding of how that measurement is made. However, more recent European Respiratory Society/American Thoracic Society guidelines for field walking tests (including 6MWT) support the use of continuous oximetry because of evidence showing that the lowest saturation does not necessarily occur at the end of the test.

Patients suspected of having desaturations by pulse oximetry during a 6MWT are regularly referred to our facility for formal cardiopulmonary exercise testing. These referrals come from physicians in the community as well as specialty clinics at our affiliated university hospital. In our experience, the referred patients have frequently undergone extensive diagnostic evaluations on the basis of their 6MWT oximetry results. These evaluations are a source of significant expense, including that of the cardiopulmonary exercise testing itself, as well as risk to the patient from invasive procedures or radiation exposure that may be unnecessary if their pulse oximetry testing results were inaccurate.

Review of 48 sequential referrals to our facility during the prior year for cardiopulmonary exercise testing revealed five referrals for suspected desaturation during ambulatory testing. Full medical records from prior to referral were not available to review for all patients. However, several of the patients had extensive evaluation prior to referral, including ventilation/perfusion scans, other diagnostic imaging, and referrals to specialty physicians. One of these patients was hospitalized for evaluation because of concern for a pulmonary embolus on the basis of their symptoms and 6MWT oximetry results.

Despite potential inaccuracies, pulse oximetry is an integral component of cardiopulmonary exercise testing. Our facility uses a forehead sensor to minimize motion artifact during exercise and a pulse oximeter that displays a waveform to provide feedback about the quality of the reading. None of these five patients desaturated during a maximal exercise test on a cycle ergometer. Their mean lactate level at peak exercise was 6.55 mmol/L (range, 2.86-9.56 mmol/L).

These findings are somewhat limited by a lack of confirmatory arterial blood gas measurements and by our use of a cycle ergometer rather than a treadmill for testing. Exercise on a treadmill has been shown to induce greater desaturation than a cycle ergometer in patients with COPD, likely due to use of a greater percentage of skeletal muscle mass with weight-bearing exercise.

Nevertheless, we recommend that when pulse oximetry is used during a 6MWT that suspected desaturations be confirmed before further diagnostic evaluation is pursued. It is important to assess the validity of the pulse oximetry measurement by viewing the waveform quality if possible and by concordance with the patient’s heart rate. However, concordance with the patient’s heart rate alone does not ensure validity of the measurement. Pulse oximetry results that do not correlate with the patient’s clinical condition should be assessed carefully. This is particularly relevant in patients without known pulmonary disease that is of sufficient severity likely to cause hypoxemia, especially if the diffusing capacity for carbon monoxide is normal, although this does not exclude the possibility of true desaturation. Unexpected results are sometimes true, but first assessing the veracity of these unexpected results can decrease unnecessary testing, health-care expenditure, and the burden of health care on patients.

References

Chan E.D. .Chan M.M. .Chan M.M. . Pulse oximetry: understanding its basic principles facilitates appreciation of its limitations. Respir Med. 2013;107:789-799 [PubMed]journal. [CrossRef] [PubMed]
 
Wasserman K. .Hansen J.E. .Sue D.Y. .et al Measurements during integrative cardiopulmonary exercise testing.Wasserman K..Hansen J.E..Sue D.Y..Stringer W.W..Sietsema K.E..Sun X.-G..Whipp B.J.. Principles of Exercise Testing and Interpretation.  :- [PubMed]journal
 
ATS Committee on Proficiency Standards for Clinical Pulmonary Function Laboratories ATS Statement: guidelines for the six-minute walk test. Am J Respir Crit Care Med. 2002;166:111-117 [PubMed]journal. [CrossRef] [PubMed]
 
Barker S.J. . “Motion-resistant” pulse oximetry: a comparison of new and old models. Anesth Analg. 2002;95:967-972 [PubMed]journal. [PubMed]
 
Jensen L.A. .Onyskiw J.E. .Prasad N.G.N. . Meta-analysis of arterial oxygen saturation monitoring by pulse oximetry in adults. Heart Lung. 1998;27:387-408 [PubMed]journal. [CrossRef] [PubMed]
 
Holland A.E. .Spruit M.A. .Troosters  .et al An official European Respiratory Society/American Thoracic Society technical standard: field walking tests in chronic respiratory disease. Eur Respir J. 2014;44:1428-1446 [PubMed]journal. [CrossRef] [PubMed]
 
Chuang M.L. .Lin I.F. .Chen S.P. . Kinetics of changes in oxyhemoglobin saturation during walking and cycling tests in COPD. Respir Care. 2014;59:353-362 [PubMed]journal. [CrossRef] [PubMed]
 
Hsia D. .Casaburi R. .Pradhan A. .Torres E. .Porszasz J. . Physiological responses to linear treadmill and cycle ergometer exercise in COPD. Eur Respir J. 2009;34:605-615 [PubMed]journal. [CrossRef] [PubMed]
 
Turner S.E. .Eastwood P.R. .Cecins N.M. .Hillman D.R. .Jenkins S.C. . Physiologic responses to incremental and self-pace exercise in COPD: a comparison of three tests. Chest. 2004;126:766-773 [PubMed]journal. [CrossRef] [PubMed]
 
Yamaya Y. .Bogaard H.J. .Wagner P.D. .Niizeki K. .Hopkins S.R. . Validity of pulse oximetry during maximal exercise in normoxia, hypoxia, and hyperoxia. J Appl Physiol. 2001;92:162-168 [PubMed]journal
 
Kaminsky D.A. .Whitman T. .Callas P.W. . DLCO versus DLCO/VA as predictors of pulmonary gas exchange. Respir Med. 2007;101:989-994 [PubMed]journal. [CrossRef] [PubMed]
 

Figures

Tables

References

Chan E.D. .Chan M.M. .Chan M.M. . Pulse oximetry: understanding its basic principles facilitates appreciation of its limitations. Respir Med. 2013;107:789-799 [PubMed]journal. [CrossRef] [PubMed]
 
Wasserman K. .Hansen J.E. .Sue D.Y. .et al Measurements during integrative cardiopulmonary exercise testing.Wasserman K..Hansen J.E..Sue D.Y..Stringer W.W..Sietsema K.E..Sun X.-G..Whipp B.J.. Principles of Exercise Testing and Interpretation.  :- [PubMed]journal
 
ATS Committee on Proficiency Standards for Clinical Pulmonary Function Laboratories ATS Statement: guidelines for the six-minute walk test. Am J Respir Crit Care Med. 2002;166:111-117 [PubMed]journal. [CrossRef] [PubMed]
 
Barker S.J. . “Motion-resistant” pulse oximetry: a comparison of new and old models. Anesth Analg. 2002;95:967-972 [PubMed]journal. [PubMed]
 
Jensen L.A. .Onyskiw J.E. .Prasad N.G.N. . Meta-analysis of arterial oxygen saturation monitoring by pulse oximetry in adults. Heart Lung. 1998;27:387-408 [PubMed]journal. [CrossRef] [PubMed]
 
Holland A.E. .Spruit M.A. .Troosters  .et al An official European Respiratory Society/American Thoracic Society technical standard: field walking tests in chronic respiratory disease. Eur Respir J. 2014;44:1428-1446 [PubMed]journal. [CrossRef] [PubMed]
 
Chuang M.L. .Lin I.F. .Chen S.P. . Kinetics of changes in oxyhemoglobin saturation during walking and cycling tests in COPD. Respir Care. 2014;59:353-362 [PubMed]journal. [CrossRef] [PubMed]
 
Hsia D. .Casaburi R. .Pradhan A. .Torres E. .Porszasz J. . Physiological responses to linear treadmill and cycle ergometer exercise in COPD. Eur Respir J. 2009;34:605-615 [PubMed]journal. [CrossRef] [PubMed]
 
Turner S.E. .Eastwood P.R. .Cecins N.M. .Hillman D.R. .Jenkins S.C. . Physiologic responses to incremental and self-pace exercise in COPD: a comparison of three tests. Chest. 2004;126:766-773 [PubMed]journal. [CrossRef] [PubMed]
 
Yamaya Y. .Bogaard H.J. .Wagner P.D. .Niizeki K. .Hopkins S.R. . Validity of pulse oximetry during maximal exercise in normoxia, hypoxia, and hyperoxia. J Appl Physiol. 2001;92:162-168 [PubMed]journal
 
Kaminsky D.A. .Whitman T. .Callas P.W. . DLCO versus DLCO/VA as predictors of pulmonary gas exchange. Respir Med. 2007;101:989-994 [PubMed]journal. [CrossRef] [PubMed]
 
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