Abstract
Dear Editor:
I read with interest the article carried out by James Hallenbeck 1 who reviews the pathophysiology of dyspnea and then discusses the possible effects of opioids on these pathophysiologies. I would like to raise a number of questions, drawing on the knowledge of the author and the readers:
1. Although several studies suggest that most opioids alleviate dyspnea, 2 from the physiological point of view, how would you justify that is morphine and no other opioids, the most related?
2. Many studies show that dyspnea in advanced cancer is usually multifactorial 3 and a significant proportion of the underlying causes are irreversible. How could two or more etiologic factors interfere pathophysiologically? Synergistically? Ever?
3. Most studies 4 show the symptomatic effect of opioids in relation to baseline dyspnea, which could be the pathophysiological explanation for not objectifing this effect on dyspnea.
4. Palliative medicine doctors know that not all patients with dyspnea respond equally to the beneficial effect of opioids. Currow and colleagues 5 failed to demonstrate how clinical effects could be associated with a greater response. Could there be any mechanism to justify that difference in pathophysiological response?
5. Abernethy and colleagues 6 demonstrated that fewer doses of morphine were required to relieve dyspnea than to relieve the pain. Would there be any model that would justify this finding?
6. Although the symptomatic response of systemic morphine in cancer patients with dyspnea is well known, the majority of randomized clinical trials have shown the beneficial effect of opioids in patients with COPD. 7 Could there be any pathophysiological reason for this?