The predictors of central and obstructive sleep apnoea in haemodialysis patients

Background. Sleep apnoea (SA) is often observed in haemodialysis patients, but there have been few studies on types of SA and their predictors. We therefore investigated the prevalence and types of SA and the associations between types of SA and clinical factors in haemodialysis patients. Methods. We initially examined nocturnal oxygen desaturation index (ODI) (desaturation of > 4%/events per hour) in 119 haemodialysis patients (68 males, mean age of 61.4 years). Patients with ODI of more than five were diagnosed as having SA. Then, 30 patients underwent polysomnography and we measured Apnoea-hypopnoea index (AHI), which was calculated as the number of apnoeas plus hypopnoeas per hour of sleep. Clinical characteristics were examined in all patients. Results. Forty-one (34.5%) of the 119 patients had SA. Twenty-seven (22.7%) of the 119 patients had SA with subjective symptoms such as daytime somnolence and snoring. There was a significant difference between body mass index (BMI) in patients with SA and that in patients without SA (22.5 vs 19.8 kg/m(2), P < 0.001). There were significantly higher prevalences of hypertension (85.4 vs 66.7%, P < 0.05) and diabetes mellitus (36.6 vs 10.3%, P < 0.01) in patients with SA than those in patients without SA. Multivariable analysis showed that BMI was independently associated with the occurrence of SA (OR 1.20, 95% CI 1.05-1.38). Mean AHI of 30 patients who underwent polysomnography was 53.2 +/- 28.9 [central apnoea, 4.1 +/- 5.6 (8%); obstructive apnoea, 21.7 +/- 21.5 (42%); mixed apnoea, 4.9 +/- 8.0 (9%); hypopnoea, 21.4 +/- 15.5 (41%)]. The number of obstructive apnoea events per hour was significantly correlated with BUN (r = 0.490, P < 0.01), Cr (r = 0.418, P < 0.05) and BMI (r = 0.489, P < 0.01) and was inversely correlated with serum bicarbonate (r = -0.646, P < 0.01) and brain natriuretic peptide (BNP) (r = -0.481, P < 0.01). The number of central apnoea events per hour was correlated inversely with PaO2 (r = -0.393, P < 0.05) and PaCO2 (r = -0.388, P < 0.05) and tended to be correlated with cardiothoracic ratio (CTR) (r = 0.347, P = 0.060). Conclusions. There is a high prevalence of SA in haemodialysis patients. The dominant type of SA in haemodialysis patients is obstructive sleep apnoea (OSA). Uraemia (BUN, Cr), metabolic acidosis (serum bicarbonate) and BMI are good predictors of OSA. PaO2, PaCO2 and CTR are good predictors of central sleep apnoea (CSA). Good management of these factors might improve SA in haemodialysis patients.