Exercise-induced oxygen desaturation in COPD patients without resting hypoxemia
Graphical abstract
A combination of certain lung function and baseline oxygen saturation characteristics revealed that the highest proportion of patients (95%) who exhibited exercise-induced oxygen desaturation (nadir-SpO2 ≤88%) are characterized by DLco <50% predicted and FEV1 <45% predicted with resting values of PaO2 <10 kPa and SpO2 <95%.
Introduction
Chronic obstructive pulmonary disease (COPD) is a highly prevalent chronic respiratory disease, characterized by partially irreversible airflow limitation (Vestbo et al., 2013). Patients with COPD frequently experience a significant fall of oxygen saturation during exercise that is attributed to the imbalance between oxygen delivery and demand during exercise (Vogiatzis and Zakynthinos, 2012). Exercise-induced oxygen desaturation (EID) has been related to reduced exercise performance, a faster decline in forced expiratory volume in the first second (FEV1), and increased mortality in patients with COPD (Casanova et al., 2008, Kim et al., 2012). Moreover, ambulatory oxygen supplementation reduces exercise-induced breathlessness and oxygen desaturation; and improves exercise performance in patients with COPD, irrespective of resting arterial oxygen pressure (Jolly et al., 2001, Somfay et al., 2001). In fact, oxygen saturation ≤88% with physical activity is currently an indication for reimbursement of continuous oxygen use by Centres for Medicare & Medicaid Services in COPD patients with resting non-hypoxemia (Stoller et al., 2010). Therefore, identifying non-hypoxemic COPD patients with EID seems clinically relevant, but has not been studied previously.
A six-minute walk test (6MWT) has been suggested as preferred measure to identify COPD patients with EID (Knower et al., 2001). Indeed, EID occurs frequently during 6MWT in patients with COPD (Jenkins and Cecins, 2011). Moreover, the 6MWT is more sensitive for identifying EID in patients with COPD compared to a cardiopulmonary exercise test (Poulain et al., 2003).
Even though the 6MWT is a relatively simple test (Salzman, 2009), several screening tests have been proposed to predict which COPD patients will (not) have EID, including FEV1, diffusion capacity for carbon monoxide (DLCO) and/or baseline standard pulse oximetry (SpO2) (Kelley et al., 1986, Knower et al., 2001, Owens et al., 1984). Indeed, Knower and colleagues suggested that a resting SpO2 of 95% or less is a good screening test for the detection of EID during a 6MWT (sensitivity: 73%; negative predictive value: 84%), especially in patients with a DLCO >36% of the predicted value (sensitivity: 100%; negative predictive value: 100%) (Knower et al., 2001). To date, this readily available office screening procedure has not been validated in a large cohort of non-hypoxemic patients with COPD.
Herein, we report a prospective analysis in a large clinical cohort of patients with COPD undergoing baseline evaluation for pulmonary rehabilitation (Spruit et al., 2008). The aim of the study was two-fold: (1) to validate the cut off of resting SpO2 of 95% or less as a simple screening procedure to predict EID during a 6MWT in patients with COPD as proposed by Knower et al. (2001); and (2) to study the characteristics of non-hypoxemic patients with COPD who have a nadir SpO2 ≤88% during the 6MWT. A priori, resting SpO2 was expected not to be accurate enough to identify non-hypoxemic patients with EID.
Section snippets
Setting and participants
Patients with COPD (Decramer et al., 2003) referred for a comprehensive pulmonary rehabilitation program at CIRO+ or its pulmonary rehabilitation network were recruited prospectively (Spruit et al., 2008). Age between 45 and 85 years was set as inclusion criterion. The use of long-term oxygen therapy and/or treatment or hospitalization for an acute exacerbation in the last 4 weeks before the study and resting hypoxemia were pre-defined exclusion criteria. The medical ethical committee of the
Patient characteristics
A total of 402 patients (age range: 45–85; mean: 64.3 years) with COPD (174 women) were included in this study. Patients generally had moderate to very severe COPD, an impaired lung diffusion capacity, a normal BMI, normal resting arterial oxygen and carbon dioxide tension, severe symptoms of dyspnea at rest, and a poor functional exercise performance. 158 patients (59%) had EID. Desaturators had a lower BMI, a higher degree of airflow limitation, worse DLCO, more static lung hyperinflation,
Discussion
The current study has two main findings: (1) baseline oxygen saturation threshold of 95% or lower measured by standard pulse oximetry fails to identify accurately EID in 402 non-hypoxemic patients with COPD; and (2) nadir SpO2 ≤88% occurs frequently during a 6MWT in non-hypoxemic patients with COPD, in particular in those patients with a FEV1 <45% predicted, DLCO <50% predicted, resting PaO2 <10 kPa, baseline SpO2 <95%, and in women.
In 2001, Knower and colleagues reported that baseline oxygen
Conclusions
In summary, EID cannot be predicted accurately by just using resting SpO2. Moreover, the current analysis revealed that 39% of the 402 non-hypoxemic patients with COPD had nadir SpO2 ≤88%, which may be suitable candidates for ambulatory oxygen therapy. Obviously, future trials have to corroborate the current findings, in particular the observed influence of gender.
Funding
Vasileios Andrianopoulos obtained an ERS Long Term Research Fellowship (LTRF 63-2012).
Acknowledgement
The authors like to thank all patients who volunteered to participate in the present study.
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On behalf of the CIRO+ Rehabilitation Network. The CIRO+ Rehabilitation Network consists of CIRO+, centre of expertise for chronic organ failure in Horn, The Netherlands; Maastricht University Medical Centre (MUMC+) in Maastricht, The Netherlands; St. Jans Gasthuis in Weert, The Netherlands; Laurentius Hospital in Roermond, The Netherlands; St. Anna Hospital in Geldrop, The Netherlands; and Elkerliek Hospital in Helmond, The Netherlands.