## 3 Results  
The Prevalence of Abnormal SpO2 Was 34.8% in the Study Population, and Approximately 10.9% of the Study Patients Had OSA  
Finally, 92 MHD patients were included in our study sample with complete medical records and follow-up. The baseline biochemical characteristics and laboratory features of the whole study population were demonstrated in Table 1. The mean age showed 62.8 \(\pm\) 10.2 years; approximately 45% were male. The mean duration of follow-up was 23.4 \(\pm\) 12.4 months. The mean body weight and BMI were 60.9 \(\pm\) 9.9 kg and 23.9 \(\pm\) 2.8 kg/m\({}^{2}\), respectively. The prevalence of DM, hypertension, OSA and CAD were 39.1%, 43.5%, 10.9% and 39.1%, respectively. According to the definition given by the Unites States Food and Drug Administration, the prevalence of abnormal pre-dialytic SpO2 was 34.8% in our observational study. The overall mortality rate was 25.0% during the 2152.8 patient-months of follow up. Among deceased patients, fifteen patients (65.2%) died from CV causes and the remaining eight (34.8%) were non-CV deaths. \begin{table}
\begin{tabular}{c c} \hline \hline
**Variables** & **Overall (\(n\) = 92)** \\ \hline Age (years) & 62.8 \(\pm\) 10.2 \\ Male, \(n\) (\%) & 43 (44.2) \\ Diabetes mellitus, \(n\) (\%) & 38 (41.3) \\ Obstructive sleep apnea, \(n\) (\%) & 10 (10.9) \\ Epworth Sleepiness Score & 8.6 \(\pm\) 1.7 \\ Hypertension, \(n\) (\%) & 40 (43.5) \\ Prior coronary artery disease, \(n\) (\%) & 36 (39.1) \\ Pre-dialytic SpO2 (\%) & 94.6 \(\pm\) 3.3 \\ Abnormal SpO2, \(n\) (\%) & 32 (34.8) \\ Body weight (kg) & 60.9 \(\pm\) 9.9 \\ Body mass index (kg/m\({}^{2}\)) & 23.9 \(\pm\) 2.8 \\ Systolic blood pressure (mmHg) & 139 \(\pm\) 26 \\ Diastolic blood pressure (mmHg) & 80 \(\pm\) 17 \\ Hemodialysis vintage (months) & 35.3 \(\pm\) 23.2 \\ Aspartate aminotransferase (IU/L) & 16.6 \(\pm\) 7.8 \\ Albumin (g/dL) & 3.9 \(\pm\) 0.5 \\ Total cholesterol (mg/dL) & 199.8 \(\pm\) 53.6 \\ Triglyceride (mg/dL) & 225.2 \(\pm\) 184.1 \\ Blood urea nitrogen (mg/dL) & 65.5 \(\pm\) 16.0 \\ Creatinine (mg/dL) & 10.3 \(\pm\) 1.7 \\ Uric acid (mg/dL) & 7.6 \(\pm\) 1.4 \\ Potassium (mmol L\({}^{-1}\)) & 4.6 \(\pm\) 0.8 \\ Adjusted calcium (mg/dL) & 9.4 \(\pm\) 0.8 \\ Phosphate (mg/dL) & 4.6 \(\pm\) 1.5 \\ Iron (\(\mu\)g/dL) & 78.5 \(\pm\) 31.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Baseline biochemical characteristics and laboratory features of the whole study population. DM, Prior CAD History, OSA, and Pre-Dialytic SpO2 Values Differed Significantly between Event and Non-Event Groups According to All-Cause and CV Mortality  
The prior CAD history, DM, prevalent OSA and pre-dialytic SpO2 values were significantly different between the death event and event-free groups according to all-cause mortality (Table 2). Specifically, the comparison between survivors and non-survivors demonstrated prior CAD history (33.3 vs. 56.5%; \(p\)-value < 0.05), DM (33.3 vs. 65.2%; \(p\)-value < 0.01); OSA (5.8 vs. 26.1%; \(p\)-value < 0.05); and pre-dialytic SpO2 value (95.2 \(\pm\) 2.2% vs. 93.0 \(\pm\) 5.0%; \(p\)-value < 0.05), respectively. Compared with the non-event group, the event group of all-cause mortality had higher prevalence of hypertension and the mean systolic and diastolic blood pressure (27 (39.1%) vs. 13 (56.5%); 136 \(\pm\) 23 vs. 148 \(\pm\) 32 mmHg; 78 \(\pm\) 14 vs. 85 \(\pm\) 24 mmHg, respectively). However, the \(p\)-value was insignificant (0.148; 0.063; 0.056, respectively). Likewise, the event group compared with the event-free group favored higher circulating levels of total cholesterol (212.3 \(\pm\) 45.0 vs. 192.3 \(\pm\) 52.8 mg/dL), lower levels of serum albumin (3.8 \(\pm\) 0.4 vs. 3.9 \(\pm\) 0.5 g/dL, \(p\) = 0.508), hemoglobin (10.2 \(\pm\) 1.4 vs. 10.8 \(\pm\) 1.4 g/dL, \(p\) = 0.116) and hematocrit (31.0 \(\pm\) 4.3 vs. 32.4 \(\pm\) 4.3%,