Acute intravenous administration of morphine perturbs sleep architecture in healthy pain-free young adults: A preliminary study

Abstract

Study Objectives: Pain is a leading cause of sleep disturbances in medical illness, Providing effective analgesia is considered an important intervention to reduce these sleep disturbances. Opioids remain the treatment of choice to relieve postoperative pain in hospitalized patients. However, their effects on sleep in pain patients or normal subjects remain unclear, as previous studies have been conducted mainly with former opioid addicts. The purpose of this investigation was to evaluate and describe the effects of acute clinical doses of morphine on sleep in healthy pain-free subjects. Design: Subjects were randomly assigned to untreated (baseline), morphine (intravenous injections of 1 mg/kg), and placebo (intravenous injections of 0.9% NaCl) conditions. Setting: Sleep laboratory. Participants: Seven healthy pain-free, nonaddicts (5 women, 2 men; mean age = 25 ± 1.6 years). Measurements and Results: Standard polysomnographic sleep and respiratory variables were measured during 3 experimental conditions. The treatment effect was analyzed with a Latin square cross-over design followed, when appropriate, by Tukey contrasts. Morphine altered sleep architecture by reducing slow-wave sleep (non-rapid eye movement stages 3-4) and rapid eye movement sleep, and by increasing non-rapid eye movement stage 2 sleep. Results did not reveal any statistical differences for other sleep and respiratory variables. Conclusions: Similar to earlier findings in animals, nondependent opiate addicts, and postoperative patients, morphine was found to reduce duration of slow-wave sleep. Unlike previous reports, however, its acute administration produced a moderate reduction in rapid eye movement sleep and did not increase correlates of arousal (ie, awakenings, electroencephalogram arousals, wake after sleep onset). Future studies should correlate these findings in patients with pain and evaluate whether optimal pain relief with opioid therapy can improve sleep disturbances in pain patients.