Assessment of Hypoxemia in Patients with Obstructive Sleep Apnea Hypopnea Syndrome using Weighted Percent of the Total Recorded Time Spent Desaturation

Objective: To develop a quantitative index named weighted percent of the total recorded time spent desaturation (WTS) to assess the severity of hypoxemia in patients with obstructive sleep apnea hypopnea syndrome (OSAHS). Methods: A group of 237 patients with complete polysomnography (PSG) data was reviewed. Multiple indices, including descriptions of various oxygen desaturation (SaO2) levels (e.g. awake (ASaO2), lowest (LSaO2), lowest SaO2 in the longest apnea duration (LASaO2), lowest SaO2 in the longest hypopnea duration (LHSaO2)), percent of the total time spent below various levels of oxygen saturation (TS%) at thresholds <90 (TS90), <85 (TS85), <80 (TS80), <75 (TS75), <70 (TS70), <65% (TS65), and WTS calculated using the weighting method in mathematics, were recorded. All indices were compared in patients with varying degrees of OSAHS using one-way analysis of variance firstly. Then all indices were compared with apnea-hypopnea index (AHI) and Epworth Sleepiness Scale (ESS) using simple linear correlation analysis and multiple linear stepwise regression analysis. In addition, another group of 103 patients with OSAHS was reviewed. The coincidences between the degree of AHI (DA) and degree of hypoxemia (DH) which was assessed using traditional hypoxemia indices such as LSaO2, TS90, and WTS were observed. Results: In the first group, multiple indices, including LSaO2, LASaO2, LHSaO2, TS90, TS85, TS80, TS75, and WTS, were associated with the degree of OSAHS. Among them, WTS index is the most consistently reported parameter associated with AHI and ESS. In the second group, the coincidences were 72.8% between DH assessed using WTS and DA, 57.3% between DH assessed using TS90 and DA, 42.7% between DH assessed using LSaO2 and DA. Conclusion: WTS index, combining time and severity of desaturation, may have high coincidence with AHI, and provide additional useful data in the study of hypoxemia, compared to other traditional indices. Such data may be important in future studies of physiological variables.