E. F. Van-dam-van-isselt, Pain in patients with COPD: a systematic review and meta-analysis, BMJ Open, vol.4, p.5898, 2014.

A. L. Lee, S. L. Harrison, R. S. Goldstein, and D. Brooks, Pain and its clinical associations in individuals with COPD: a systematic review, Chest, vol.147, pp.1246-1258, 2015.

C. R. Borge, A. K. Wahl, and T. Moum, Pain and quality of life with chronic obstructive pulmonary disease, Heart Lung, vol.40, pp.90-101, 2011.

B. Hajghanbari, S. J. Garland, J. D. Road, and W. D. Reid, Pain and physical performance in people with COPD, Respir Med, vol.107, pp.1692-1699, 2013.

S. B. Bentsen, C. Miaskowski, and T. Rustøen, Demographic and clinical characteristics associated with quality of life in patients with chronic obstructive pulmonary disease, Qual Life Res, vol.23, pp.991-998, 2014.

A. Romem, Pain management at the end of life: A comparative study of cancer, dementia, and chronic obstructive pulmonary disease patients, Palliat Med, 2015.

J. M. Habraken, Health-related quality of life in end-stage COPD and lung cancer patients, J Pain Symptom Manage, vol.37, pp.973-981, 2009.

M. H. Roberts, D. W. Mapel, A. Hartry, A. Von-worley, and H. Thomson, Chronic pain and pain medication use in chronic obstructive pulmonary disease. A cross-sectional study, Ann Am Thorac Soc, vol.10, pp.290-298, 2013.

Z. Ahmadi, E. Bernelid, D. C. Currow, and M. Ekström, Prescription of opioids for breathlessness in end-stage COPD: a national population-based study, Int J Chron Obstruct Pulmon Dis, vol.11, pp.2651-2657, 2016.

N. T. Vozoris, Incident opioid drug use among older adults with chronic obstructive pulmonary disease: a population-based cohort study, Br J Clin Pharmacol, vol.81, pp.161-170, 2016.

N. T. Vozoris, Incident opioid drug use and adverse respiratory outcomes among older adults with COPD, Eur. Respir. J, vol.48, pp.683-693, 2016.

M. P. Ekström, A. Bornefalk-hermansson, A. P. Abernethy, and D. C. Currow, Safety of benzodiazepines and opioids in very severe respiratory disease: national prospective study, BMJ, vol.348, p.445, 2014.

D. J. Janssen, S. M. De-hosson, E. Bij-de-vaate, K. J. Mooren, and A. A. Baas, Attitudes toward opioids for refractory dyspnea in COPD among Dutch chest physicians, Chron Respir Dis, vol.12, pp.85-92, 2015.

J. Perrone, L. S. Nelson, and D. M. Yealy, Choosing Analgesics Wisely: What We Know (and Still Need to Know) About Long-Term Consequences of Opioids, Ann Emerg Med, vol.65, pp.500-502, 2015.

J. A. Hoppe, H. Kim, and K. Heard, Association of emergency department opioid initiation with recurrent opioid use, Ann Emerg Med, vol.65, pp.493-499, 2015.

J. R. Landis and G. G. Koch, The measurement of observer agreement for categorical data, Biometrics, vol.33, pp.159-174, 1977.

S. R. Cole and M. A. Hernán, Constructing inverse probability weights for marginal structural models, Am. J. Epidemiol, vol.168, pp.656-664, 2008.

S. Bailly, R. Pirracchio, and J. F. Timsit, What's new in the quantification of causal effects from longitudinal cohort studies: a brief introduction to marginal structural models for intensivists, Intensive Care Med, vol.42, pp.576-579, 2016.

J. F. Foss, E. Orelind, and L. I. Goldberg, Effects of methylnaltrexone on morphine-induced cough suppression in guinea pigs, Life Sci, vol.59, pp.235-238, 1996.

H. L. Rittner, N. Roewer, and A. Brack, The clinical (ir)relevance of opioid-induced immune suppression, Curr Opin Anaesthesiol, vol.23, pp.588-592, 2010.

A. Jennings, A. N. Davies, J. P. Higgins, J. S. Gibbs, and K. E. Broadley, A systematic review of the use of opioids in the management of dyspnoea, Thorax, vol.57, pp.939-944, 2002.

D. C. Currow, Once-daily opioids for chronic dyspnea: a dose increment and pharmacovigilance study, J Pain Symptom Manage, vol.42, pp.388-399, 2011.

D. Viglino and M. Maignan, Opioids and adverse outcomes in elderly chronic obstructive pulmonary disease patients, Eur. Respir. J, vol.48, p.1817, 2016.

H. Barnes, J. Mcdonald, N. Smallwood, and R. Manser, Opioids for the palliation of refractory breathlessness in adults with advanced disease and terminal illness, Cochrane Database Syst Rev, vol.3, p.11008, 2016.

D. A. Mahler, American College of Chest Physicians consensus statement on the management of dyspnea in patients with advanced lung or heart disease, Chest, vol.137, pp.674-691, 2010.

D. D. Marciniuk, Managing dyspnea in patients with advanced chronic obstructive pulmonary disease: a Canadian Thoracic Society clinical practice guideline, Can. Respir. J, vol.18, pp.69-78, 2011.

L. Pisani, N. S. Hill, A. M. Pacilli, M. Polastri, and S. Nava, Management of Dyspnea in the Terminally Ill, Chest, vol.154, pp.925-934, 2018.

G. Rocker, J. Bourbeau, and J. Downar, The New 'Opioid Crisis': Scientific Bias, Media Attention, and Potential Harms for Patients with Refractory Dyspnea, J Palliat Med, vol.21, pp.120-122, 2018.

J. Constantin, Remifentanil-based sedation to treat noninvasive ventilation failure: a preliminary study, Intensive Care Med, vol.33, pp.82-87, 2007.

G. Rocker, Palliation of dyspnoea in advanced COPD: revisiting a role for opioids, Thorax, vol.64, pp.910-915, 2009.

J. A. Wedzicha, S. E. Brill, J. P. Allinson, and G. C. Donaldson, Mechanisms and impact of the frequent exacerbator phenotype in chronic obstructive pulmonary disease, BMC Med, vol.11, p.181, 2013.

J. R. Hurst, Susceptibility to exacerbation in chronic obstructive pulmonary disease, N. Engl. J. Med, vol.363, pp.1128-1138, 2010.