Pulse oximetry is useful for screening sleep apnoea syndrome in dialysis patients.

Abstract

Sir, Sleep apnoea syndrome (SAS) is characterized by repetitive nocturnal hypoxia, while it is also known to be a risk factor for cardiovascular disease [1]. The prevalence of SAS in dialysis patients has been shown to range from 20 to 50% in comparison to a range of 2–4% in the general population [2,3]. Although the main type of SAS in the general population is obstructive type, SAS in dialysis patients includes features of both central and obstructive types [3]. Moreover, uraemia and metabolic acidosis are good predictors of SAS in dialysis patients [3]. The gold standard diagnostic test for SAS is overnight polysomnography (PSG). However, PSG is costly in terms of both time and money. Pulse oximetry and Epworth Sleepiness Scale (ESS), a questionnaire about daytime sleepiness have been widely used to screen for obstructive SAS because these are simple and easy methods to perform [4,5]. However, no screening method for SAS in dialysis patients has yet been clearly evaluated. The purpose of this study is to evaluate the usefulness of pulse oximetry and ESS for screening SAS in dialysis patients. We studied 54 maintenance haemodialysis (HD) patients [male: 50%, age: 66.0 ± 24.2 years, diabetes mellitus: 39.9%, duration of HD: 5.7 ± 5.1 years and BMI: 22.7 ± 9.1] in Koga Red Cross Hospital during the period from April 2004 to March 2005. Patients with active malignancy and pulmonary disease were excluded. The validity of the pulse oximetry was confirmed by the synchronous recording of both PSG (Morpheus, Teijin Pharma Ltd, Japan) and pulse oximetry (PULSOX-Me300, Teijin Pharma Ltd, Japan) on dialysis day. We used the 3% oxygen desaturation index (ODI) and 4% ODI by pulse oximetry as a screening marker. In addition to pulse oximetry, ESS was used to investigate daytime sleepiness. We compared the apnoea–hypopnoea index (AHI) by PSG to 3% ODI, 4% ODI and ESS scores, respectively. Using a cutoff of AHI≥15 and 3% ODI (4% ODI) ≥15, the sensitivity and specificity were 100% (76.0%) and 55.2% (93.1%) respectively (Table ​(Table1).1). On the other hand, the sensitivity and specificity using a cutoff of AHI≥15 and ESS scores≥11 were 20.0% and 82.8% respectively (Table ​(Table11). Table 1 Sensitivity and specificity of pulse oximetry/ESS scores screening for SAS in dialysis patients (n = 54) Both 3% ODI and 4% ODI were significantly correlated with AHI (3% ODI: r = 0.657, P < 0.0001; 4% ODI: r = 0.618, P < 0.0001) (Figure ​(Figure1).1). However, no significant correlation was seen between ESS scores and AHI (r = 0.149, P = 0.283) (Figure ​(Figure11). Fig. 1 Correlation between AHI and 3% ODI (A)/ESS scores (B) in dialysis patients (n = 54). In dialysis patients, pulse oximetry is superior to ESS for detecting SAS. The less efficacy of ESS may be due to the unique characteristics of SAS in dialysis patients [2,3]. We therefore suggest that pulse oximetry is useful for screening SAS in dialysis patients. Conflict of interest statement. None declared.