APAP = auto positive airway pressure
The device is set to a certain range of pressure and the pressure then fluctuates depending on the need of the patient throughout the night.
Many home care companies, those who provide and sell the device, place patients on APAP without knowing what the exact pressure needed for patients.
Often it does the trick of treating patient who have simple obstructive sleep apnea. However, it is generally not advised if a patient has complex medical history such as chronic pain, heart trouble or neurological disorders.
If you are not doing well on CPAP, then you should seek consultation from your local sleep doctors.