One of the Leading Causes of Sleep Disturbanc- Es in Medical Illness Is Pain. Sleep Disturbances

ONE OF THE LEADING CAUSES OF SLEEP DISTURBANCES IN MEDICAL ILLNESS IS PAIN. SLEEP DISTURBANCES ARE REPORTED BY MORE THAN 70% OF patients suffering from painful disorders, including chronic rheumatic diseases, headaches, postherpetic neuralgia, burn injuries, and postoperative pain to name a few.1-5 Pain and other elements of the illness influence and alter the sleep process.6 Reciprocally, disturbances in sleep structure may decrease pain thresholds and interact with the illness and further contribute to daytime symptoms.5,6 Even though there are limited data suggesting that pain relief is sufficient to improve sleep in patients with acute or chronic pain, it is often assumed that effective pain relief is the most helpful intervention to reduce sleep disturbances in such patients.4,7 However, most medications used to treat pain also alter sleep architecture. For example, studies have shown that analgesics such as acetylsalicylic acid and nonsteroidal anti-inflammatory drugs can increase awakenings and reduce both slow-wave sleep (SWS) and rapid-eye movement (REM) sleep.8,9 Although animal studies show that opioids alter sleep,10-12 there is a paucity of information on the effects of opioids on sleep in humans in pain. For example, 1 study observed sleep disturbances in hospitalized patients after the administration of morphine or other opioids.13 Nonetheless, studies conducted in clinical settings are also faced with many other confounding factors such as pain, anxiety, and nonconducive sleep environment and are, therefore, not able to establish independent effects of morphine on sleep. Furthermore, a recent study suggests that severe sleep disturbances are present in a postoperative setting regardless of whether patients received local anesthetics or opioids.14 There are surprisingly few experimental studies describing the effects of morphine or other opioids on normal human sleep. In fact, other than the little information from published abstracts,15,16 the current state of knowledge on this subject originates mainly from the evaluation of former opioid-dependent prisoners.17-19 Even though these studies did not use standard sleep-scoring criteria, their results suggest that morphine increases nocturnal wakefulness and decreases REM and SWS sleep in a dose-dependent manner.17-19 However, this may not be the case clinically, as most patient populations comprise of individuals with little or no prior exposure to opioids. Furthermore, when former opioid addicts are compared with normal subjects, they show a differential Acute Intravenous Administration of Morphine Perturbs Sleep Architecture in Healthy Pain-Free Young Adults: a Preliminary Study