If you have been diagnosed with sleep apnea and your doctor mentioned CPAP therapy, you may have quickly discovered there are three types — CPAP, BiPAP, and APAP — and nobody told you which one you actually need. This article explains exactly what each machine does, who it is for, and why the choice matters for how well your treatment actually works.
Why the Machine Type Matters
All three devices deliver pressurised air through a mask to keep your airway open during sleep. But they do it differently. Prescribing the wrong type does not just reduce comfort — it can result in incomplete treatment, where apneas continue to occur despite using the device every night. Getting the right machine is as important as using it consistently.
CPAP — Continuous Positive Airway Pressure
CPAP delivers one fixed pressure throughout the night — the same pressure on every breath, all night long. A titration study (in-lab or auto-detected) determines the specific pressure required to keep your airway open, and that pressure is programmed into the machine.
Who it is for
CPAP works well for patients with consistent, predictable obstruction — where the airway collapses at roughly the same pressure throughout the night regardless of sleep position or sleep stage. It is the original gold-standard treatment and remains effective for many patients.
The main limitation
Fixed pressure means you are breathing against the same resistance whether you are in light sleep, deep sleep, on your back, or on your side. Many patients find exhaling against fixed pressure uncomfortable — particularly at higher settings. This is the most common reason people abandon CPAP.
APAP — Auto-Titrating Positive Airway Pressure
APAP is the same concept as CPAP, but instead of one fixed pressure, the machine adjusts pressure breath-by-breath within a range you and your doctor set. A pressure of 6–14 cmH₂O, for example, means the machine can deliver anywhere from 6 to 14 depending on what it detects in your airway in real time.
Who it is for
APAP is the preferred first-line treatment for most patients with obstructive sleep apnea at Respire. It handles variation in pressure requirements — which change with sleep position, REM sleep, alcohol, weight fluctuation, and nasal congestion — far better than fixed CPAP. The average delivered pressure is typically lower than fixed CPAP, which improves comfort and compliance significantly.
The main advantage
Because it adapts in real time, APAP effectively self-titrates. Patients who have never had an in-lab titration study can often start on APAP and achieve therapeutic AHI levels within the first two weeks. The machine data (downloaded at your follow-up) confirms whether the set range is appropriate.
BiPAP — Bilevel Positive Airway Pressure
BiPAP delivers two separate pressures: a higher IPAP (inspiratory positive airway pressure) when you breathe in, and a lower EPAP (expiratory positive airway pressure) when you breathe out. The pressure difference between the two is what makes breathing feel more natural.
Who it is for
BiPAP is prescribed in specific situations — not as a default upgrade from CPAP. The main indications are:
- Central sleep apnea (CSA): Where the brain fails to signal breathing — CPAP alone is insufficient and can worsen central events.
- Overlap syndrome: COPD and OSA coexisting — higher pressure requirements and CO₂ retention make BiPAP necessary.
- CPAP intolerance at high pressures: When required pressure exceeds 15 cmH₂O, exhaling against it is very difficult — BiPAP resolves this.
- Hypoventilation syndromes: Obesity hypoventilation syndrome, neuromuscular disease, or chest wall disorders.
What BiPAP does not do
BiPAP is not simply "more comfortable CPAP." It is a clinically different prescription for specific indications. Switching to BiPAP without an appropriate diagnosis does not improve treatment and adds unnecessary cost.
How to Know Which One You Need
The decision is based on your diagnosis, AHI severity, home sleep study or PSG results, comorbidities, and how you tolerate the initial device. Here is a simplified guide:
- Straightforward OSA (mild to moderate): APAP first line
- Severe OSA or known fixed pressure requirement: CPAP or APAP
- Central sleep apnea: BiPAP (specifically BiPAP-ST or ASV)
- COPD + OSA overlap: BiPAP
- CPAP intolerant at high pressure: BiPAP or APAP with wider range
What About Mask Type?
The machine is only half the equation. The mask determines whether therapy actually works in practice. Nasal pillow masks work for most patients, particularly side sleepers and those with claustrophobia. Nasal masks handle moderate pressure well. Full-face masks are needed for mouth breathers. A correctly fitted mask eliminates most of the common complaints about PAP therapy — noise, leaks, dry mouth, and aerophagia. At Respire, mask fitting is done by our team — not left to the patient to figure out at home.
The Follow-Up Is Not Optional
Starting PAP therapy without follow-up at 4–6 weeks is one of the most common mistakes. The machine stores data — AHI achieved on therapy, leak rate, usage hours, and pressure distribution. Reviewing this data is the only way to confirm that treatment is working. Many patients feel better subjectively but still have an AHI of 10–15 on therapy — which means the disease is partially treated. A single data review appointment catches this and allows adjustment. See how we manage sleep apnea at Respire →