Summary and Comment: Impact of Obstructive Sleep Apnea in Hemodialysis Patients

Haemodialysis Patients with Sleep Apnoea Syndrome Experience Increased Central Adiposity andAlteredMuscular Composition and Functionality. Sakkas GK, Gourgoulianis KI, Karatzaferi C, Liakopoulos V, Maridaki MD, Pastaka C, Lavdas E, Soher BJ, Dovas S, Fezoulidis I, Hadjigeorgiou GM, Stefanidis I. Nephrol Dial Transplant 23:336–344, 2008 Among the many comorbid conditions associated with end-stage renal disease (ESRD), one that is often under-recognized is sleep apnea. Sleep apnea is characterized by abnormal respiratory patterns during sleep (apnea, hypopnea) and disturbed sleep (snoring, restlessness) resulting in daytime sleepiness and fatigue which may reduce quality of life (QoL) and functional capacity. Based on polysomnographic testing, sleep apnea is often defined as an apnea–hypopnea index (AHI) > 5—more than five apnea and hypopnea episodes per hour. The prevalence of sleep apnea in the general population is around 20% (1), whereas in hemodialysis (HD) patients, cohort studies have reported sleep apnea prevalence rates ranging from 30% to 80% depending upon the definition used and if the diagnosis is based upon self-report questionnaires or polysomnography (2–4). Risk factors for sleep apnea include obesity, smoking, and diabetes. The hypoxic episodes that occur with sleep apnea are thought to result in sympathetic nervous system activation, endothelial dysfunction, inflammation, and oxidative stress, which may be associated with arterial hypertension and other adverse cardiovascular outcomes (5–8). Treatment ofmild sleep apnea involves lifestyle modifications such as weight loss and changing sleeping positions. Moderate to severe sleep apnea can be treated with continuous positive airway pressure (CPAP) with improvement in sleep quality, daytime functioning, and blood pressure. As in the general population, sleep apnea in HD patients is associated with increased cardiovascular disease risk and reduced sleep quality (9–12). Decreased sleep quality among dialysis patients has been linked to decreased QoL and increased healthcare utilization. Because sleep apnea is a treatable condition with potentially important adverse consequences, its timely diagnosis and treatment is important. This observational study (13) sought to define the impact of sleep apnea upon the functional status and QoL of chronic HD patients. Patients underwent polysomnography, dual energy X-ray absorptiometry (DEXA), computerized tomography (CT) scanning, andmeasurement of waist-to-hip ratios (WHR) to determine adipose tissue distribution and body composition. Functional capacity was determined by walk tests and sit-to-stand cycles. QoL was determined using the SF-36 questionnaire. Subjects were divided into two groups according to high (>5) or low (£5) AHI. At baseline, the group with high AHI (n = 22) was significantly older (mean age 60.6 vs. 47.9 years, p = 0.01), and had greater body mass index (BMI; 26.5 vs. 23.5 kg ⁄m, p = 0.01), dialysis vintage (2.4 vs. 1.6 years, p = 0.01), and WHR (1.0 vs. 0.9, p = 0.01) than those with low AHI (n = 21). Contrary to other studies, QoL scores were similar in the two groups. The absence of a difference in QoL scores in this study may have been due to the small sample size and short duration of the study; alternatively, the impact of sleep apnea on QoL may be overshadowed by the effects of other comorbidities and of other aspects of having ESRD. Subjects in the high AHI group had impaired functional capacity as measured by walk tests and sit-to-stand ratios. The groupwith highAHI also had greater central adiposity, with CT scans demonstrating greater visceral adipose tissue (67.5 vs. 41.8%, p = 0.01), visceral to total adipose tissue ratio (0.5 vs. 0.3, p = 0.01), visceral to subcutaneous adipose tissue ratio (0.9 vs. 0.5, p = 0.01), and thigh muscle extramyocellular lipids (22.4 vs. 17.7 cm, p = 0.01) in the high AHI compared with low AHI groups. DEXA scan measurements were not different between the two groups. While this was a small study of cross-sectional design involving a single dialysis unit, other cohort studies in HD patients have found a strong association between BMI and the presence of sleep apnea (14), an association that has been reported in the general population as well (15). Sakkas et al. (13) propose that reduced sleep quantity and poor sleep quality resulting from sleep apnea may lead to diminished functional capacity as has been suggested in the general population (16,17). Address correspondence to: Jeffrey S. Berns, MD, FASN, University of Pennsylvania School of Medicine, 3400 Spruce Street, 1 Founders, Philadelphia, PA 19104-4206, or e-mail: jeffrey.berns@uphs.upenn. edu. Seminars in Dialysis—Vol 22, No 3 (May–June) 2009 pp. 308–310 DOI: 10.1111/j.1525-139X.2009. 00572.x a 2009 Copyright the Authors. Journal compilation a 2009 Wiley Periodicals, Inc.