APAP results in lower mean airway pressure compared to CPAP

The use of APAP therapy, in lieu of fixed CPAP, has become the norm for many practitioners of sleep medicine treating patients with OSA. From a practical standpoint, APAP does not require a preceding in-laboratory titration, and thus affected patients can get started on therapy more proximately to their diagnosis. In addition, because APAP varies the amount of pressure administered based upon event detection algorithms, with an effort to provide the lowest pressure necessary to maintain airway patency, the mean airway pressure provided by APAP is generally significantly lower than that provided by CPAP. As a result, APAP has been proposed as preferable to CPAP in patients who have poor tolerance of high pressures throughout the night. APAP also provides an advantage for patients with significant night-to-night variability as can be seen in patients with position-dependent or alcohol-dependent OSA.

Several randomized trials have shown that patients treated with APAP demonstrate slightly greater use of therapy than those treated with CPAP, although this difference is quite modest, usually on the order of less than 15 min per night. This increased use of therapy has not been associated with any improvement in functional status or subjective sleepiness. Patients treated with APAP tend to have slightly higher residual AHIs than those treated with CPAP; this is likely due to the tendency of the former device to use to lowest effective pressure throughout the night.

While the exact mechanism by which APAP detects fluctuations in airflow (and thus can determine whether it should adjust pressure upwards) varies from device to device, all of the algorithms used for this purpose depend upon maintenance of modest leak levels; significant leak can prevent the device from detecting events and titrating upwards, leading to a greater degree of residual disease. Other potential barriers to APAP effectiveness include the presence of central apneas, which are often not accurately identified by the machine, and thus may result in a counterproductive further increase in PAP level.1

Footnotes

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