Sleep Apnea Terminology

by  Find-A-Code
January 3rd, 2018

According to CGS and Noridian Medicare Administrative Contractors, the following terms and their definitions are linked to the prescription and use of positive airway pressure devices for the treatment of obstructive sleep apnea. Apnea: The cessation of airflow for at least 10 seconds.

Apnea-Hypopnea Index (AHI): The average number of episodes of apnea and hypopnea per hour of sleep without the use of a positive airway pressure device. Respiratory effort related arousals (RERAs) are not included in the calculation of the AHI. Sleep time can only be measured in a Type I or (facility based polysomnogram) Type II sleep study.

BiPAP: Bilevel positive airway pressure device, which provides two settings (different from CPAP which only offers a continuous high pressure air flow). A BiPAP device allows settings for a prescribed pressure and exhalation pressure; allowing patients to exhale more easily and not fight against a continuous or high pressure airflow.

CPAP: Continuous positive airway pressure device consists of a mask hooked to a pump that forces a steady stream of pressurized air through obstructed, or partially obstructed, airway passages to keep them open while sleeping.

Hypopnea: An abnormal respiratory event lasting at least 10 seconds associated with at least a 30% reduction in thoracoabdominal movement or airflow as compared to baseline, and with at least a 4% decrease in oxygen saturation.

Obstructed Sleep Apnea (OSD): A serious disorder in which the patient repeatedly starts and stops breathing, for periods of 10 seconds or more, while sleeping, due to the muscles of the throat relaxing and blocking the airway.

Respiratory Disturbance Index (RDI): The average number of apneas plus hypopneas per hour of recording without the use of a positive airway pressure device. (RERAs) are not included in the calculation of the RDI. The RDI is reported in Type III and Type IV, and Other home sleep studies.


Sleep Apnea Terminology. (2018, January 3). Find-A-Code Articles. Retrieved from

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