Document ID: chunk:federal_register_of_legislation:F2023L00203:clause:1_120
Version: federal_register_of_legislation:F2023L00203
Segment Type: clause
Provision Reference: sch 1 cl 120
Character Range: 81968–82914

120     An overnight sleep study is used to define the severity of sleep-related disorders of breathing and can be used to define impairment after appropriate treatment has been implemented. During the overnight sleep study there is continuous monitoring of breathing pattern, respiratory effort, arterial oxygen saturation, electrocardiogram, and sleep state. Results of sleep studies cannot readily be expressed in terms of a percentage of predicted values. Consequently, impairment is rated by assigning scores to the degree of abnormality at sleep study (Figure 2-B: Calculating obstructive sleep apnoea score and Table 2.4: WPI derived from obstructive sleep apnoea score). These ratings are based on frequency of disordered breathing, frequency of sleep disturbance, degree of hypoxaemia and, as appropriate, hypercapnoea during sleep. In addition, degree of daytime sleepiness is assessed using the Epworth sleepiness scale (Johns, 1991).