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(Chest. 2001;120:437-443.)
© 2001 American College of Chest Physicians

Effects of Supplemental Oxygen During Activity in Patients With Advanced COPD Without Severe Resting Hypoxemia*

Enrique C. Jolly, MD; Valentina Di Boscio, MD, FCCP; Laura Aguirre, MD; Carlos M. Luna, MD, FCCP; Sara Berensztein, MD and Ricardo J. Gené, MD

* From the Division of Pulmonary Diseases (Drs. Jolly, Di Boscio, Aguirre, Luna, and Gené) and Division of Cardiology (Dr. Berensztein), Department of Internal Medicine, Hospital de Clínicas "José de San Martín," Buenos Aires University, Buenos Aires, Argentina.

Correspondence to: Enrique C. Jolly, MD, Larrea 67–11° "A," 1030 Buenos Aires, Argentina; e-mail: ejolly{at}intramed.net.ar


   Abstract
TOP
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 Conclusion
 References
 
Study objectives: To assess oxygen desaturation during activities and to evaluate the short-term effects of supplemental O2 use in patients with severe COPD who do not qualify for long-term O2 therapy.

Design: A double-blind, randomized, placebo-controlled trial.

Setting: Outpatients from the pulmonary diseases division of a tertiary-care university hospital.

Patients: Twenty patients with stable COPD with FEV1/FVC ratios of < 50%, FEV1 levels < 55% of the predicted normal value, and PaO2 levels of > 60 mm Hg when resting.

Interventions: Patients were initially evaluated with pulmonary function tests, blood gas analysis, and Doppler echocardiography, and they underwent the following three 6-min walking tests (WTs) in a random sequence: basal WT (BWT); WT while breathing compressed air (CAWT); and WT while breathing O2 (O2WT).

Measurements and results: The distance walked was recorded in meters. Dyspnea was measured by Borg scale measurement before and after the tests, and arterial oxygen saturation measured by pulse oximetry (SpO2) was continuously monitored. Results were analyzed by grouping patients in the following manner: desaturators (DSs) (ie, patients with a drop in SpO2 of at least 5% and < 90% during the WT) vs nondesaturators (NDSs); and O2 responders (ie, patients with an increase of at least 10% in the distance walked and/or a decrease of at least 3 points in Borg index score) vs nonresponders. During the BWT, 11 of 20 patients (55%) were defined as desaturators. During the O2WT, the SpO2 remained at > 90% in every patient. The distance walked increased by 22% (p < 0.02), and dyspnea decreased 36% (p < 0.01) in DS patients. In NDS patients, O2 administration reduced dyspnea by 47% (p < 0.001), but the distance walked did not improve. Responses were markedly different from one patient to another. No significant differences were noticed between the results of the BWT and CAWT in any of the groups. Thirteen O2 responders did not differ from 7 nonresponders either in basal data or in desaturation measure during the BWT, except that all walking responders (five patients) were above the median of basal left ventricle performance.

Conclusions: Most of the studied COPD patients desaturated during the BWT. O2 administration avoided desaturation and could increase the distance walked and reduce dyspnea, but these effects were not related to walking desaturation in individual cases. Improvements were not a placebo effect. The therapeutic role of O2 during activities in some patients with severe COPD needs to be individually assessed.

Key Words: COPD • daily living activity • exercise-induced hypoxemia • exercise-induced dyspnea • left ventricle performance • oxygen therapy


   Introduction
TOP
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 Conclusion
 References
 
Long -term oxygen therapy is the only treatment that has been shown to improve survival in COPD patients with severe hypoxemia, based on the number of hours of daily use.1 2 There are well-established physiologic criteria for prescribing home oxygen.3 4 However, some patients do not meet these criteria during rest, but significant hypoxemia occurs during exertion.5 6 Some studies7 8 9 have found that the short-term benefits of oxygen during exertion include increased exercise performance and reduction in dyspnea. However, other studies did not confirm these findings.10 In fact, there is even a controversy about a placebo effect.7 8 9 10 11 12 The long-term benefits of oxygen when used during exercise alone are unknown.

There are no widely accepted evidence-based criteria for prescribing oxygen only during daily living activities (DLAs) in COPD patients without hypoxemia during rest.7 11 13 14 15 Medicare indications are a PaO2 level of 55 mm Hg or an arterial oxygen saturation (SaO2) level of 88% documented during exercise, but there are no reasons to consider beforehand that only exercise desaturators would benefit with oxygen. There is a need for information about which COPD patients could benefit from such therapy.

To further clarify these points, we conducted a randomized, double-blind, placebo-controlled trial in order to assess desaturation during exercise in COPD patients, and to evaluate the short-term effects of oxygen therapy on dyspnea and performance during activities in COPD patients without resting hypoxemia.


   Materials and Methods
TOP
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 Conclusion
 References
 
Patients
We studied 20 COPD patients (American Thoracic Society grade II/III16 ) with at least 30 days of clinical stability before inclusion in the study, who were recruited from a respiratory rehabilitation program. The protocol was explained to each subject, and they signed an informed consent form, as approved by the institutional review board.

The inclusion criteria were the following: (1) FEV1 < 55% of predicted and/or FEV1/FVC ratio < 50%; and (2) resting PaO2 level of > 60 mm Hg. Patients with peripheral vascular disease, cardiac failure, or active coronary heart disease were excluded.

Initial Assessment
All patients underwent pulmonary function testing. Spirometry was performed according to American Thoracic Society recommendations,16 maximal voluntary ventilation was measured in 12 s, pulmonary volumes were measured by N2 washout, maximal inspiratory pressure was corrected according to residual volume, maximal expiratory pressure was corrected according to total lung capacity, and single-breath diffusing capacity of the lung for carbon monoxide (DLCO) was measured using appropriate equipment (CAD/Net System 1070; Medical Graphics Co; St. Paul, MN).

Measurements of resting arterial blood gas levels while the patients were breathing room air were obtained during a period of clinical stability and were measured with a blood gas analyzer (model ABL3, Radiometer; Copenhagen, Denmark).

Cardiac morphology and ventricular function were evaluated by Doppler echocardiography while the patient was resting. Systolic pulmonary artery pressure was estimated in patients with tricuspid insufficiency. Fractional shortening, obtained by subtracting the left ventricular systolic dimensions from the diastolic dimensions and expressed as a percentage of the diastolic dimensions, was considered to be a global measurement of left ventricular systolic function.

Walking Tests
Performance during a 6-min walking test (WT)17 was considered to be a reliable parameter of DLAs. All patients had been familiarized previously with this test, which was practiced in a hospital corridor 30 m long.

Every patient performed three WTs during the same day, with at least a 45-min interval between each test. The first test (the basal WT [BWT]) was performed with the patient breathing room air. Then every patient was randomized to perform the following: a WT while breathing compressed air (CAWT) and, with an interval of at least 45 min, a WT while breathing oxygen (O2WT); or an O2WT and, with an interval of at least 45 min, another CAWT. Half of the patients were located in each segment.

Two indistinguishable cylinders located at the middle of the corridor, one with compressed air (CA) and one with oxygen, were connected by a Y-piece to a 15-m tube ending in a nasal cannula. One person, who knew the randomly assigned sequence, opened the valve and regulated the gas flow as requested by another technician, who walked behind the patient recording the SaO2 measured by pulse oximetry (SpO2) values. Both this technician and the patient were blind about which gas was added.

Tests with added gas were arbitrarily initiated at a flow of 3 L/min. Gas flow was progressively increased to 6, 9, and then 12 L/min if the SpO2 level decreased to < 90% or if it decreased by 2% from the value of the previous minute.

During each test, the distance was measured in meters. SpO2 level and cardiac rate were measured by a pulse oximeter (model 515 A; Novametrics; Warlington, CT) every minute. The final SpO2 level was the end-exercise saturation reading. Gas flow also was recorded every minute. Immediately before and after a test, the dyspnea index was evaluated with the Borg scale.18 Ventilatory patterns during tests were not recorded.

Data Analysis
The data collected were analyzed in the following two ways. First, patients were divided into desaturator (DS) and nondesaturator (NDS) groups according to the SpO2 behavior during the BWTs. We arbitrarily considered those patients whose SpO2 levels decreased by at least 5% and fell to < 90% to be DS patients. Data from both groups were compared. Second, patients also were divided into oxygen responder and oxygen nonresponder groups. We arbitrarily considered those patients who increased their walking distance by > 10% and/or decreased their Borg index score by at least 3 points from those of their BWTs to be oxygen responders. Data were compared between both groups.

To look for a relationship between basal measured variables and changes in the walked distance or dyspnea index during the O2WT, we analyzed the distribution of responders and nonresponders around each variable median.

Statistical Analysis
Results are presented as the arithmetic mean ± SEM. Results from different tests performed by the same subjects were compared by Student’s t test for paired samples. Results from tests performed by different subjects were compared by Student’s t test for unpaired samples. Nonparametric variables were compared by {chi}2 test. A p value of < 0.05 was considered to be significant.

To evaluate the short-term oxygen effects on the WT results, we computed the change in walked distance and dyspnea index in every patient as a percentage of basal data, and then we looked for the arithmetical mean of those changes in the group.


   Results
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 Conclusion
 References
 
Prevalence of Desaturation
No patient increased SpO2 during BWT. SpO2 remained constant in 5% of patients (one patient). A decrease of at least 4% in SpO2 was seen in 85% of the patients (17 patients). A drop of at least 5% in SpO2 was observed in 70% of the patients (14 patients).

SpO2 decreased by at least 5% and fell to < 90% in 11 patients (55%). These 11 patients were grouped as DS patients. The remaining nine patients, whose arterial saturation was always > 90%, comprised the NDS group.

Prediction of Desaturation
There were no significant differences between DS and NDS patients in demographics, or in the results of basal lung function testing, resting arterial blood gas analysis, or cardiology evaluation. Despite this, there was a trend toward lower PaO2 and DLCO levels in DS patients.

During the BWT, distance, cardiac rate, and initial Borg dyspnea index score were similar in both groups. The final Borg dyspnea index score and the minimum level of SpO2 achieved during the BWT were the only significant differences between them (Table 1 ). Neither a basal parameter nor the results of the BWT allowed us to predict the occurrence of oxygen desaturation during tests.


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  		Table 1. Basal Data of DS and NDS Groups*

 
Gas Administration
During the O2WT, a flow of 3 L was required by 13 patients, 6 L was required by 3 patients, and 9 L was required by 4 patients. During the CAWT, a flow of 3 L was required by one patient, 6 L was required by seven patients, 9 L was required by nine patient, and 12 L was required by four patients. As flows were gradually increased, high flows were administered just for a couple of minutes and were acceptably tolerated.

Response to Oxygen Therapy
In DS patients, oxygen administration avoided critical desaturation during WT, so that no patients had their SpO2 levels fall to < 90%. The distance walked increased in 10 of 11 DS patients. These increases were expressed as a percentage of BWT (Table 2 and Fig 1 ). There was a wide range of increases (range, 2 to 100%), with an average of 22%. The final dyspnea index decreased in 8 of 11 DS patients. These improvements ranged from 1 to 6 points, with an average of 2.09 points, which represent 36% from the basal mean (Table 2 and Fig 2 ).


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  		Table 2. DS Group*

 


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  		Figure 1. Dyspnea index (Borg scale). Individual response to O2 and CA in patients grouped according to SpO2 level during BWTs. NS = not significant.

 


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  		Figure 2. Distance walked (expressed as a percent of the basal data). Individual response to O2 and CA in patients grouped according to SpO2 level during BWTs. See the legend of Figure 1 for any abbreviations not used in the text.

 
In NDS patients, oxygen administration did not significantly modify the distance walked in relation to the basal test, but it did decrease dyspnea index by an average of 47.4% (Table 3 ).


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  		Table 3. NDS Group*

 
There were important differences in individual responses. Only 4 of 11 DS patients increased the distance walked by > 10%, and 5 of 11 DS patients improved the dyspnea index score by > 2 points. Individual results are presented in Figures 1 and 2 .

Oxygen Responders
Five patients (three DS patients and two NDS patients) increased the distance walked by at least 10% during the O2WT. Seven patients (four DS patients and three NDS patients) experienced a decrease in Borg index score of at least 3 points. One other DS patient fulfilled both conditions. A comparison of these responders (n = 13) and nonresponders (n = 7) is presented in Table 4 .


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  		Table 4. Basal Data of Oxygen Responder and Nonresponder Groups*

 
Responders were evenly distributed below and above the median of each basal variable, except for walking responders with respect to the fractional shortening measured by the basal Doppler echocardiography. The median of the fractional shortening was 42%, and all six walking responders were above that level.

Response to CA
CA administration did not significantly modify the results of the basal tests in any group (Tables 2 , 3 and Figs 1 , 2 ).


   Discussion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
Conclusion
 References
 
Our results show that most patients desaturated during activity and that no basal parameter allowed us to predict it. Oxygen administration avoided critical desaturation in every patient and improved dyspnea index scores among DS and NDS patients. Oxygen therapy also increased the distance walked only in the DS group. CA administration consistently produced no improvement in distance walked or dyspnea index score. Results that were more unexpected than oxygen benefits were the important differences in individual responses to oxygen from one patient to another. The individual response seemed barely related to desaturation levels during the BWT, and no other basal parameter could be considered to be a reliable predictor of the response to oxygen therapy.

We selected saturation assessed during a WT because it seemed to be a parameter that reflected the most demanding situations during DLAs. Walking has been reported to be associated with the lowest mean SaO2 value and the highest number of desaturations, when saturation was measured during different daytime activities like eating, bathing, moving, resting, and nebulization therapy.19

The predictors of exercise-induced desaturation in COPD patients without resting hypoxemia have been studied in several articles. Some have reported that the basal DLCO,6 20 FEV1 20, and/or FEV1/FVC ratio6 are sensible parameters to predict exercise-induced desaturation, and others5 9 11 have failed in finding those or other variables to be helpful.

A DLCO level of > 20 mL/min/mm Hg or 70% of the predicted value was proved to be helpful in identifying patients who were unlikely to desaturate during exercise, as was an FEV1/FVC ratio of > 50%.6 These values are unlikely in patients with severe COPD, and, in fact, all of our patients had values below those values. In our study, basal characteristics could not predict desaturation during WTs, but basal PaO2 and DLCO tended to be lower in DS patients, probably reflecting disease severity. The Borg index score at the end of the BWT was higher (p < 0.05) in DS patients, suggesting some relationship between dyspnea and exercise-induced desaturation. A larger number of patients perhaps could make these differences significant, but no value for these variables could be useful as a cutoff.

Oxygen therapy improved activity performance in the DS group. The distance walked increased an average of 22%, although with important individual differences. In fact, the conditions of only 4 of 11 patients really improved > 10% (Fig 1 , 2) .

Another relevant oxygen effect was the improvement in dyspnea index among DS and NDS patients. Oxygen therapy during the WT decreased the perceived dyspnea by 36% (2 points on the Borg scale) in the DS group and by 47.4% (2.09 points on the Borg scale) in the NDS group. Eight of 20 patients had decreases in Borg scale score of > 2 points.

Our responders did not differ from nonresponders in age, basal spirometric data, arterial blood gas levels, or systolic pulmonary artery pressure. The desaturator rate in responders (8 of 13 patients) was similar to that in nonresponders (3 of 7 patients). Fractional shortening was unique in predicting a nonresponse in distance walked. No patient with fractional shortening that was less than the median (42%) increased the distance walked while breathing oxygen. Although this value is within the normal range, it suggests that cardiovascular limitation could be implicated in the response to oxygen therapy during exercise in some patients with severe COPD.

The short-term benefits of oxygen administration during exercise have been reported in previous articles7 8 9 in patients with COPD and also specifically in patients with dyspnea who had other pulmonary diseases. Our results differ from other reports7 8 as we did not find any placebo effect when administering CA under double-blind conditions, so we considered it to be a valuable therapeutic action.

Several articles7 8 9 10 11 have previously described improvements in dyspnea index and exercise performance when oxygen was administered only during exercise. Some of them stated the difficulties in predicting the response to oxygen9 and specifically described the lack of relationship between short-term oxygen effects and desaturation during exercise.8 9 10 11 The wide range of individual responses is highlighted by almost all of these authors.7 9 11 Our results agreed with those of Lock et al7 that, as a group, patients who desaturated during exercise improved performance, as measured by the number of meters walked, with oxygen therapy. Although, when considering individual patients, some of them showed that they could respond to oxygen therapy irrespective of their desaturation during the BWT.

The aforementioned benefits and the possible reparative effects of oxygen support the recommendation of oxygen use only during exercise in COPD patients with mild hypoxemia while resting. Desaturation during exercise does not seem to be a reliable criterion for the selection of patients to whom oxygen should be prescribed during activities. As the response to this therapy is unpredictable, it is mandatory to evaluate it in every patient.

It is not clear which oxygen response justifies its indication during activities. Improvements of 10%7 or 50%14 from baseline activity have been considered to be necessary by different authors. Probably any increase in performance, even as low as 10% from baseline, could represent a desirable improvement due to the severe impairment in patients with advanced COPD. Also, there is no agreement about what level of decrease in the dyspnea index is relevant enough to indicate oxygen therapy during activity. Authors have reported a decrease of >= 10%8 and of >= 2 points in the used scale8 10 11 as sufficient effects to indicate prescribing oxygen therapy.


   Conclusion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Conclusion
References
 
Most patients with advanced COPD who do not meet the accepted criteria for long-term oxygen therapy experience desaturation during DLAs. Oxygen therapy during a WT avoids desaturation and decreases the dyspnea index score irrespective of desaturation levels. It also increases activity performance in some patients. These improvements are not a placebo effect, and most of these patients would achieve relevant benefits from portable oxygen during DLAs. But the response to oxygen therapy could not be predicted either by basal evaluation or by desaturation during WT, so it needs to be specifically measured.

Because the effects on survival from avoiding desaturation during DLAs remain unevaluated, the only reason to indicate oxygen therapy to these patients is to achieve symptomatic improvement. The wide variation in individual responses indicates the need to test each patient with oxygen before prescribing it.


   Footnotes
 
Abbreviations: BWT = 6-min walking test performed while breathing room air; CA = compressed air; CAWT = 6-min walking test performed while breathing compressed air; DLA = daily living activity; DLCO = diffusing capacity of the lung for carbon monoxide; DS = desaturator; NDS = nondesaturator; O2WT = 6-min walking test performed while breathing oxygen; SaO2 = arterial oxygen saturation; SpO2 = arterial oxygen saturation measured by pulse oximetry; WT = 6-min walking test

Received for publication July 13, 2000. Accepted for publication March 21, 2001.


   References
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Conclusion
 References
 

  1. . Nocturnal Oxygen Therapy Trial Group. (1980) Continuous or nocturnal oxygen therapy in hypoxic chronic obstructive lung disease: a clinical trial. Ann Intern Med 93,391-398
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  3. Zielinski, J, Sliwinski, P (1991) Indications for and methods of long-term oxygen therapy. Eur Respir Rev 1,536-540
  4. . American College of Chest Physician-National Heart, Lung, and Blood Institute (1984) ACCP-NHLBI National Conference on Oxygen Therapy. Chest 86,234-247[Free Full Text]
  5. Freitag, AP, Summers, E, Hamilton, AL, et al (1995) Behavior of arterial oxygen saturation during exercise in normal subjects and patients with pulmonary and cardiac impairment. Chest 108,140S
  6. Ries, AL, Farrow, JT, Clausen, JL (1988) Pulmonary function tests cannot predict exercise-induced hypoxemia in chronic obstructive pulmonary disease. Chest 93,454-459[Abstract/Free Full Text]
  7. Lock, SH, Paul, EA, Rudd, RM, et al (1991) Portable oxygen therapy: assessment and usage. Respir Med 85,407-412[Medline]
  8. Booth, S, Kelly, MJ, Cox, NP, et al (1996) Does oxygen help dyspnea in patients with cancer? Am J Respir Crit Care Med 153,1515-1518[Abstract]
  9. Woodcock, AA, Gross, ER, Geddes, DM (1981) Oxygen relieves breathlessness in "pink puffers." Lancet 1,907-909[ISI][Medline]
  10. Dewan, NA, Bell, W (1994) Effect of low flow and high flow oxygen delivery on exercise tolerance and sensation of dyspnea. Chest 105,1061-1065[Abstract/Free Full Text]
  11. Dean, NC, Brown, JK, Himelman, RB, et al (1992) Oxygen may improve dyspnea and endurance in patients with chronic obstructive pulmonary disease and only mild hipoxemia. Am Rev Respir Dis 146,941-945[ISI][Medline]
  12. O’Donnell, DE, Webb, KA (1992) Breathlessness in patients with severe chronic airflow limitation. Chest 102,824-831[Abstract/Free Full Text]
  13. . American Thoracic Society. (1995) Standards for the diagnosis and care of patients with chronic obstructive pulmonary disease. Am J Respir Crit Care Med 152(suppl),S77-S120
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