Polysomnography has demonstrated severe sleep abnormalities in patients nursed in the ICU. They include increased sleep latencies, sleep fragmentation (rapid changes in sleep stage), increases in stage I sleep, and decreased REM sleep. A number of often coexisting factors contribute to the resultant sleep deprivation (Table 1).
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Table 2 Etiology of sleep disturbance in the ICU
Patients with chronic obstructive airways disease and restrictive pulmonary disease are commonly admitted to the ICU with exacerbation of their underlying condition. Typically these patients show increased sleep latencies, and decreased total sleep time and REM sleep. Furthermore, frequent arousals related to hypoxemia, hypercarbia, coughing, and treatment with methylxanthines decrease the time spent in NREM sleep. Obstructive sleep apnea, an under-recognized condition characterized by cyclical upper airway obstruction resulting in hypoxemia and hypercarbia, produces fragmented sleep with frequent arousals and sleep stage changes. Its estimated prevalence is 2 to 4 per cent of the adult male population, and therefore its presence in the ICU, either as the primary disorder or complicating another condition, is common.
The hypoxemia that accompanies sleep may exacerbate myocardial ischemia in patients with coronary artery disease. Nocturnal angina is well recognized and is often related to REM sleep. It may be aggravated by an increase in ventricular ectopy and the autonomic changes associated with sleep. Following myocardial infarction, sleep efficiency may be disrupted for up to 9 days. Patients with congestive heart failure, particularly when associated with Cheyne-Stokes respiration, show increases in stage I sleep with marked decreases in NREM sleep. Arousals are common and are often related to the hyperventilation phase of Cheyne-Stokes respiration.
Sleep disturbance may occur as a consequence of neurological disorders affecting central sleep mechanisms (e.g. in myotonic dystrophy and progressive supranuclear palsy). However, sleep disruption due to neurological disease is most commonly associated with conditions which affect the respiratory pathways, leading to nocturnal hypoventilation and sleep disruption as a consequence of microarousals. Neuromuscular disorders and primary muscle disease may present with respiratory insufficiency and sleep disorders either primarily or in the postoperative period. Examples of such disorders include motor neuron disease, multiple sclerosis, hereditary sensorimotor neuropathy, inflammatory muscle disease, and acid maltase deficiency.
Sleep disturbance is commonly reported in patients with chronic renal failure and consists of a decrease in total sleep time and NREM sleep. Obstructive sleep apnea is common in patients receiving hemodialysis, and the periodic limb movements common in patients with chronic renal failure may contribute to the sleep disruption.
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