If you have a nightly AHI (Apnea-Hypopnea Index) of more than 5 events of any kind per hour, you are considered at risk and need refinement of existing treatment or to start treatment.

If you have persistent CSAs (central sleep apnea), which the RESMED clan call 'open airway', then a BiPAP will not serve you well. You need what is called an ASV (adaptive-servo-ventilator). They cost an arm and a couple of your legs, but you can look on the open market, or even get a good used one, for a lot less than the DMEs will sell you one (Durable Medical Equipment suppliers). It is a shame that so many sleep experts and DME sellers will suggest that BiPAP machines will help someone with CSA. They do not. A BiPAP will help to stent the airway when pressures are insufficient to those set as the main settings by adjusting flow to suit the need. That is not how to treat CSAs.