Excellent post by DB above. For more information, do a Google search for
respiratory drive You will find terms like hypoxic and hypercapnic drive.
Also see
Insurance Guidelines for bilevel and ASV. This summary from Resmed is pretty good.
Getting ASV approval is a difficult process, as a medical necessity must be established for the equipment. The patient must try CPAP and it must be proven ineffective in order to progress to bi-level. Then bi-level must also be failed and a medical justification written that non-invasive ventilation is necessary and in the doctor's opinion will be beneficial.
Medicare will cover a bi-level respiratory assist device without backup (this is what they call a bi-level or BiPAP) for patients with obstructive sleep apnea if the patient meets the criteria for PAP therapy (outlined above) and:
CPAP is tried and proven ineffective based on therpeutic trial conducted in either a facility (sleep center) or home setting.
A face-to-face clinical re-evaluation is completed during the 3-month trial period. The physician must document that the following issues were addressed prior to changing from CPAP:
Mask fit and comfort (read more about different types of mask and how they fit here)
CPAP pressure setting prevent tolerating therapy and lower settings were tried, but failed to:
Control symptoms of OSA; or
Improve sleep; or
Reduce AHI/RDI to acceptable levels
If the patient switches to a bi-level device within the 3-month trial, the length of the trial is not changed as long as there are at least 30 days remaining. If less than 30 days remain of the trial period, re-evaluation must occur before the 120th day (following the same criteria as CPAP adherence).