Oxygen desaturation and adverse events during 6-min walk testing in patients with COPD

bs_bs_banner ORIGINAL ARTICLE Oxygen desaturation and adverse events during 6-min walk testing in patients with COPD MARY M. ROBERTS,1,2 JIN-GUN CHO...
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Oxygen desaturation and adverse events during 6-min walk testing in patients with COPD MARY M. ROBERTS,1,2 JIN-GUN CHO,1,3 JACQUELINE S. SANDOZ1,4 AND JOHN R. WHEATLEY1,2,3 1 Respiratory Ambulatory Care Service, Western Sydney Local Health District, 2Ludwig Engel Centre for Respiratory Research, Westmead Millennium Institute, Westmead, 3Westmead Clinical School, Sydney Medical School, University of Sydney, Sydney, New South Wales, Australia, and 4Division of Respiratory Medicine, Ottawa Hospital, Ottawa, Ontario, Canada

ABSTRACT Background and objective: The 6-min walk test (6MWT) is a simple test assessing functional capacity, but concerns about risks of substantial oxygen desaturation in pulmonary patients have led to nonadherence to the standardised American Thoracic Society guideline. We evaluated the safety of the 6MWT in stable COPD patients and compared the incidence of adverse events in patients with and without substantial exertional hypoxaemia. Methods: 6MWT data were obtained for 1136 patients with moderate to very severe COPD. Demographics, adverse events, oxygen saturation (SpO2), 6-min walk distance, lung function and quality of life measures were compared between patients with substantial exertional hypoxaemia (nadir SpO2 < 85%) and those without (SpO2 ≥ 85%). Comparisons were made using Mann–Whitney U-test for continuous variables and Fisher’s exact test for categorical variables. Results: Twenty-five patients (2.2%) had adverse events, the most common being dizziness, chest tightness, chest pain and palpitations. Substantial exertional hypoxaemia did not increase the incidence of adverse events. No significant morbidity or mortality was recorded. Patients with adverse events had lower baseline SpO2, worse quality of life scores, and higher depression and anxiety scores. However, no significant differences were seen in anthropometric data, spirometric values or SpO2 during and after the 6MWT. Conclusions: Asymptomatic exertional hypoxaemia is not associated with an increased incidence of adverse events during 6MWT in COPD patients. Our data support the ATS guideline that the 6MWT should be continued in the absence of symptoms and that intermittent oximetry monitoring does not assist in preventing adverse events.

Correspondence: Jin-Gun Cho, Department of Respiratory and Sleep Medicine, Westmead Hospital, PO Box 533, Wentworthville, NSW 2145, Australia. Email: jin.cho @sydney.edu.au Received 31 July 2014; invited to revise 5 September 2014; revised 30 October 2014; accepted 20 November 2014 (Associate Editor: Neil Eves). Article first published online: 20 January 2015 © 2015 Asian Pacific Society of Respirology

SUMMARY AT A GLANCE Concerns about significant oxygen desaturation during the 6MWT have led to test cessation or application of supplemental oxygen. Oxygen desaturation during 6MWT in our cohort of COPD patients did not increase the incidence of adverse events during the test. Oxygen desaturation alone is not an indication to stop the 6MWT.

Key words: chronic obstructive pulmonary disease, exercise and pulmonary rehabilitation, hypoxaemia, oxygen desaturation, respiratory function test. Abbreviations: 6MWD, 6-min walk distance; 6MWT, 6-min walk test; ATS, American Thoracic Society; AUC, area under receiver operating characteristic curves; COPD, chronic obstructive pulmonary disease; GOLD, Global Initiative for Chronic Obstructive Lung Disease; HADS, Hospital Anxiety and Depression Scale; SGRQ, St George Respiratory Questionnaire; SpO2, oxygen saturation; WSLHD, Western Sydney Local Health District.

INTRODUCTION The 6-min walk test (6MWT) is a well-established, validated exercise test that assesses functional capacity by measuring the total distance walked over a 6-min period.1 This standardised test is cost-effective, easy to administer and does not require complicated medical equipment. The 6-min walk distance (6MWD) has prognostic value in chronic obstructive pulmonary disease (COPD),2–4 interstitial lung diseases5–7 and pulmonary arterial hypertension,8,9 and may assist in the timing of lung transplantation in end-stage lung disease.10 The American Thoracic Society (ATS) guideline for the 6MWT reviews the protocol and indications for testing, in addition to recommended safety measures.1 Specifically, the guideline suggests that pulse oximetry during testing is optional, but if performed, recommends baseline oxygen saturation (SpO2) values and not constant monitoring during the Respirology (2015) 20, 419–425 doi: 10.1111/resp.12471

420 exercise test.1 In addition, Enright11 states that electrocardiography and SpO2 monitoring are not necessary during the test and that pulse oximeters may be affected by motion artefact, leading to reduced accuracy when compared with arterial blood gas samples.12,13 However, concerns regarding the safety of significant oxygen desaturation in patients with underlying chronic lung disease have led to suggestions to modify the ATS guideline to include continuous pulse oximetry during the 6MWT.14 In order to assess the incidence of any adverse events during 6MWT associated with arterial oxygen desaturation, we reviewed safety data from a large cohort of COPD patients undergoing 6MWT (with pulse oximetry measurement) during assessment for a comprehensive pulmonary rehabilitation programme.

METHODS Patients We performed a retrospective review of 1136 COPD patients referred for clinical assessment prior to pulmonary rehabilitation, who underwent 6MWT through the Respiratory Ambulatory Care Service located in the Western Sydney Local Health District (WSLHD), New South Wales, Australia. Assessments were conducted at two university teaching hospital centres (Westmead and Blacktown Hospitals). The assessment clinic involved medical, nursing and physiotherapy reviews prior to the decision to undertake 6MWT. All patients were referred for pulmonary rehabilitation with a diagnosis of COPD (postbronchodilator forced expiratory volume in 1 s (FEV1)/forced vital capacity ratio

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