Background: Chronic opioid therapy for pain management has increased dramatically without adequate study of potential deleterious effects on breathing during sleep. Methods: A retrospective cohort study comparing 60 patients taking chronic opioids matched for age, sex, and body mass index with 60 patients not taking opioids was conducted to determine the effect of morphine dose equivalent on breathing patterns during sleep. Results: The apnea-hypopnea index was greater in the opioid group (43.5/h vs 30.2/h, p < .05) due to increased central apneas (12.8/h vs 2.1/h; p < .001). Arterial oxygen saturation (SpO2) in the opioid group was significantly lower during both wakefulness (difference 2.1%, p < .001) and non-rapid eye movement (NREM) sleep (difference 2.2%, p < .001) but not during rapid eye movement (REM) sleep (difference 1.2%) than in the nonopioid group. Within the opioid group, and after controlling for body mass index, age, and sex, there was a dose-response relationship between morphine dose equivalent and apnea-hypopnea (p < .001), obstructive apnea (p < .001), hypopnea (p < .001), and central apnea indexes (p < .001). Body mass index was inversely related to apnea-hypopnea index severity in the opioid group. Ataxic or irregular breathing during NREM sleep was also more prevalent in patients who chronically used opioids (70% vs 5.0%, p < .001) and more frequent (92%) at a morphine dose equivalent of 200 mg or higher (odds ratio = 15.4, p = .017). Conclusions: There is a dose-dependent relationship between chronic opioid use and the development of a peculiar pattern of respiration consisting of central sleep apneas and ataxic breathing. Although potentially significant, the clinical relevance of these observations remains to be established.
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