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Sleep complaints are common in patients with renal disease. Many studies have assessed end-stage renal disease (ESRD) patients treated with chronic dialysis. Strub et al. (49) evaluated 22 dialysis patients, finding that 14 (63%) of these patients reported sleep disturbances characterized by reduced, fragmented sleep, and increased wakefulness during the night. Holley et al. (50) subsequently assessed sleep quality in 48 hemodialysis patients and 22 continuous ambulatory peritoneal dialysis patients, comparing their perceptions of sleep with 41 healthy subjects. Approximately 50% of the dialysis patients complained of sleep problems, as opposed to only 12% of healthy control subjects. The most common sleep complaints were trouble falling asleep (67%), night-time awakening (80%), early morning awakening (72%), restless legs (83%), and jerking legs (28%). Many of these patients complained of daytime sleepiness, and dialysis patients reported napping an average of 1.1 ± 1.3 hours daily. Polysomnographic evaluations of such patients have confirmed disrupted sleep, with reduced total sleep times, low sleep efficiencies, frequent arousals, and increased periods of wakefulness throughout the night. Polysomnographic studies have also revealed that sleep architecture is usually "lighter," with increased amounts of NREM stage 1 and 2 sleep, and decreased amounts of NREM stage 3, 4, and REM sleep.

OSA also commonly occurs in patients with ESRD. Kimmel et al. (51) performed polysomnography on 30 ESRD patients, of whom 26 were on hemodialysis. Twenty-two of these 30 patients had symptoms suggestive of OSA, and 16 (73%) of these symptomatic patients were found to have clinically significant OSA. More recent studies have confirmed prevalence rates for OSA between 30% and 80% in the ESRD population, which is much greater than reported for the general population. The frequency and severity of OSA do not appear to vary substantially between patients treated with chronic hemodialysis and continuous ambulatory peritoneal dialysis.

This increased risk for OSA in the ESRD population is not well understood. It has been proposed that hypocapnia occurring as a respiratory response to metabolic acidosis and acidemia may predispose patients to an unstable respiratory pattern (52). Beecroft et al. (53) determined that ESRD patients with concurrent OSA have augmented responsiveness of both central and peripheral chemoreflexes, which could promote OSA by destabilizing respiratory control. Upper airway edema as a component of generalized volume overload could promote the development of OSA in this population. It has also been suggested that uremic toxins may depress the central nervous system, thereby reducing upper airway muscle tone during sleep. Both OSA and ESRD are more likely to present in older populations. In a possibly related fashion, dialysis for ESRD has been associated with hormonal changes that emulate the postmenopausal state in women. It has been established that the post-menopausal state substantially increases the risk for OSA in the female gender.

Therapy for OSA in the ESRD population usually includes CPAP therapy. It has also been reported that the use of bicarbonate-based versus acetate-based dialy-sate can decrease OSA severity. Hanly and Pierratos (54) reported that switching patients from the typical three times weekly daytime hemodialysis to more frequent, slower nocturnal hemodialysis sessions reduced the mean AHI from 25 to 8 events per hour in 14 ESRD patients. Tang et al. (55) reported that shifting from continuous ambulatory peritoneal dialysis to nocturnal peritoneal dialysis significantly reduced AHI in ESRD patients. The potential benefit from these changes in dialysis protocol clearly warrants further investigation.

Patients with ESRD frequently complain of daytime sleepiness, which has been confirmed by multiple sleep latency tests and maintenance of wakefulness tests. Potential contributors to daytime sleepiness could include underlying sleep disorders, such as OSA, restless legs syndrome (RLS), and periodic limb movement disorder (PLMD), all of which are more prevalent in the ESRD population. It has also been suggested that a subclinical uremic encephalopathy may be present in dialysis patients that may promote sleepiness (56). There is evidence that dialysis itself may predispose patients to somnolence, in that increased production of somno-genic cytokines, interleukin-1 and TNF-alpha, has been observed in association with both hemodialysis (57) and peritoneal dialysis (58). Therapy for problematic daytime sleepiness in this population remains focused upon treatable underlying causes, including OSA, RLS, PLMD, and insufficient sleep.

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