ABSTRACT
BackgroundThe 6-Minute Walk Test (6MWT) is a standardised method routinely used to screen for and monitor interstitiel lunge disease and/or pulmonary arterial hypertension in patients with systemic sclerosis (SSc). Studies shows that esaturations during the 6MWT are associated with severity of pulmonary manifestations in patients with SSc [1]. Digital sensors are commonly used to measure peripheral oxygen saturation (SpO2) during the 6MWT. However, digital-based sensors may have important limitations in patients with SSc due to disease-related microangiopathy, Raynaud's phenomenon, sclerodactyly and motion artifacts during the 6MWT [2]. Sensors located at more central body positions may therefore be more accurate as these as less prone to Raynaud attacks.ObjectivesTo determine the validity and re-test reliability of peripheral oxygen saturation measured at the finger, forehead, and ear during the 6MWT in patients with SSc.Methods82 patients with SSc had an arterial line placed while performing the 6MWT. Peripheral oxygen saturation was simultaneously measured by finger, forehead, and earlobe sensors and compared to the arterial oxygen saturation (SaO2) measured before and after the 6MWT. 40 patients repeated the 6MWT one week later. We used Bland-Altman plots to display the agreement between SpO2 and SaO2, and between the minimal SpO2 (minSpO2) one week apart. The intraclass correlation coefficient (ICC, 95% confidence interval 95% CI]) for repeated measurement of minSpO2 was calculated.ResultsThe mean difference (SpO2 - SaO2, ± standard deviation [SD]) after the 6MWT was –3.3% (±4.82), 0.15% (±1.55), and 1.36% (±1.93) for the finger, forehead, and earlobe, respectively (Table 1).The finger minSpO2 also demonstrated the poorest re-test reliability: The mean difference in minSpO2 (visit2-visit1, ±SD) was 1.28% (±5.3), 0.74% (±4.36) and –1.10% (±2.87),). The ICC (95% CI) showed good agreement using the ear and forehead probe (ICCear = 0.89 [0.80;0.94];ICCforehead = 0.88 [0.60;0.87]), while a modest reliability was found using the finger probe (ICCfinger = 0.65 [0.43;0.80]).ConclusionPeripheral oxygen saturation should be measured using either the earlobe or forehead during the 6MWT in patients with SSc.References[1]Villalba, W. O. et al. Six-minute walk test for the evaluation of pulmonary disease severity in scleroderma patients. Chest 131, 217–222 (2007).[2]Pathania, Y. S. Alternatives for erroneous finger probe pulse oximetry in systemic sclerosis patients during COVID-19 pandemic. Rheumatol. Int. 41, 2243–2244 (2021).Table 1.Validity and re-test reliability of peripheral oxygen during the 6MWT (n= 82)Finger probeForehead probeEar probeMean difference SpO2 - SaO2 Mean difference pre-test (+/-SD)–0.68% (±1.88)0.13% (±1.26)1.54% (±0.69) Mean difference post--test (+/-SD)–3.30% (±4.82)0.15% (±1.55)1.36% (±1.93)Mean difference of the minSpO2 (visit2-visit1) Mean difference (±SD)1.28% (±5.3)0.74% (±4.36)1.10% (±2.87)Abbreviations: SpO2, Peripheral oxygen saturation;SaO2, Arterial oxygen saturation;SD, Standard deviation.Acknowledgements:NIL.Disclosure of InterestsAmanda Lynggaard Riis: None declared, Esben Naeser Paid instructor for: Boehringer Ingelheim Denmark, Katja Thorup Aaen: None declared, Henrik Hovgaard: None declared, Peter Juhl-Olsen: None declared, Elisabeth Bendstrup Speakers bureau: Hoffman-la-Roche.Boehringer Ingelheim.Glaxo Smith Kleine.Daichii Sankyo, Klaus Soendergaard Speakers bureau: Boehringer Ingelheim, Consultant of: Boehringer Ingelheim, Grant/research support from: Boehringer Ingelheim.