A Study of Sleep Disorders in Patients with Chronic Kidney Disease (CKD)

Abstract

Sleep apnea is an important comorbidity in patients with chronic kidney disease (CKD). Although the increased prevalence of sleep apnea in patients with CKD is well established, few studies have examined the full spectrum of kidney function. We sought to determine the prevalence of sleep apnea and associated nocturnal hypoxia in patients with CKD. We hypothesized that the prevalence of sleep apnea would increase progressively as kidney function declines. 45 patients were recruited from outpatient nephrology clinics, nephrology department, and hemodialysis units. All patients completed an overnight inpatient polysomnograhy test to determine the prevalence of sleep apnea (AHI ≥ 5 events /h) and nocturnal hypoxia (oxygen saturation (SaO2) below 90% for ≥12% of the nocturnal monitoring time). Patients were stratified according to their estimated glomerular filtration rate (eGFR) at the time of the study visit into three groups as follows: CKD stage 2 (eGFR 60 to 89 mL/min/1.73 m2) (control group), CKD stages 3 and 4 (eGFR 15 to 59 mL/min/1.73 m2), and CKD stage 5 (eGFR less than 15 mL/min/1.73 m2). eGFR was calculated using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation. Out of the 45 patients included in our study with the full spectrum of kidney function, ranging from those with eGFR 60 to 89 ml/min./1.73m2 to patients with eGFR less than 15 ml/min./1.73m2, 15 (33.3%) had sleep apnea (Mean AHI; 8.71±5.86). Our study found that prevalence of sleep apnea increased as kidney function declined (Group (I), 20%; Group (II), 36.4%; Group (III), 37.5%). Furthermore, severity of sleep apnea increased as kidney function declined (Group (I), mean AHI: 5.75±0.35; Group (II), mean AHI: 6±1.38; Group (III), mean AHI: 10.6±7.04). We also found that prevalence of nocturnal hypoxia which is characteristically associated with sleep apnea was greater among groups (II) and (III) (27.3% and 16.7%, respectively) than in group (I) (10%). Severity of nocturnal hypoxia increased as kidney function declined (Group (I), 13%; Group (II), 13.6±1.22%; Group (III), 16.75±3.30%). Overall, 8 out of the 45 studied CKD patients (17.8%) had nocturnal hypoxia (Mean SaO2 below 90% for ≥12% of the nocturnal monitoring time; 15.1±2.87%). Our study revealed that as kidney function declined, Apnea/Hypopnea (AHI) indices increased, oxygen desaturation indices increased, minimal peripheral capillary oxygen saturation values decreased, peripheral capillary oxygen saturation time less than 90% increased, and snore indices increased. Also, respiratory distress index (RDI) was higher among groups (II) and (III) than in group (I). However, only differences between groups as regards respiratory distress events, respiratory distress indices, snore events, and snore indices were statistically significant. These results show that as kidney function declines, several respiratory parameters deteriorate during sleep. In addition, wake events and indices, and sleep stage 1 (%) increased as kidney function deteriorated. Sleep efficiency (%) was highest among group (I) patients and lower among groups (II) and (III), Light sleep (%) was lowest among group (I) patients and higher among groups (II) and (III), and deep sleep (%) was highest among group (I) patients and lower among groups (II) and (III). It is clear from the above results that as kidney function declines, sleep efficiency deteriorates, wake indices increase, light sleep (%) increases, and deep sleep (%) decreases. We concluded that prevalence and severity of sleep apnea in patients with CKD increase as kidney function declines. Almost 18% of patients with CKD experience nocturnal hypoxia, which may contribute to loss of kidney function.