CPAP Titration for Sleep Apnoea
On this page
Direct answer
Five centimetres of water is where CPAP titration begins, raised in 1 cm H2O increments held at least 5 minutes each, until apnoeas, hypopnoeas, respiratory-effort-related arousals, snoring and flow limitation are abolished in all stages and positions — above all supine REM, the state in which the upper airway is most collapsible. The ceiling is conventionally about 20 cm H2O: if events persist at 15 or pressure intolerance develops, conversion to bilevel positive airway pressure is the standard move, and rising central events at higher pressures (treatment-emergent central sleep apnoea) call the strategy into question rather than the dose. The final report quotes an optimal or reasonable pressure — commonly the 90th-95th percentile pressure in auto-titrating devices — because adherence, not the number alone, decides whether therapy succeeds.
What you must remember
- Titration grammar: start 5 cm H2O, increase by 1 cm H2O (held at least 5 minutes per AASM convention) until apnoeas, hypopnoeas, RERAs, snoring and flow limitation are abolished across stages and positions; decreases are permitted for aerophagia or intolerance.
- Pressure landmarks: minimum 5, maximum about 20 cm H2O; persistent events at 15 or intolerance prompt bilevel (an IPAP-EPAP difference of 4-5 cm H2O a common start).
- The supine REM rule: a titration is not complete until supine REM has been observed on effective pressure — a pressure that works in N2 sleep in the lateral position routinely fails in supine REM.
- Treatment-emergent central apnoea: complex apnoea appears when pressure itself unloads the stretch receptors; the answer is reassessment, lower pressures, or bilevel backup-rate therapies in selected patients — not simply more pressure.
- Mask and leak management: a large leak invalidates event scoring — refit before interpreting pressure rises as failure; mouth leak on a nasal mask calls for a chin strap or full-face interface.
- Split-night context: titration performed in the second half of a diagnostic study follows the same rules, with the caveat that a short REM representation may under- or over-shoot the final pressure, and follow-up review is expected.
- Auto-CPAP and downloads: auto-titrating devices prescribe ranges; adherence review — hours per night (4 hours the conventional adequate-use threshold), residual AHI (below 5) and leak — makes follow-up objective.
- Non-pressure sequelae: weight loss lowers required pressure; alcohol and supine sleep raise it; nasal obstruction needs treatment before pressure can succeed.
One titration night, stepwise
A 47-year-old with severe OSA (diagnostic AHI 42) begins at 5 cm H2O with a nasal mask. By 7 cm the apnoeas have gone, but the flow contour stays scalloped and arousals persist — flow limitation, the pressure's next task. At 9 cm in stage N2 he sleeps quietly; the scorer waits for REM. At 2 am, supine REM arrives and the events return, and the pressure walks up to 12 cm, where REM runs clean. The morning answer: optimal pressure 12 cm H2O, noting that central-looking events appeared at 14 cm — treatment-emergent central apnoea kept under review. The prescription comes with an adherence plan — device download at four weeks for hours of use, residual AHI and leak — because a perfect number worn two hours a night is a failed therapy.
Where students slip
Quoting "increase until apnoeas stop" is the incomplete answer: apnoeas stop first, hypopnoeas next, flow limitation and RERAs last — titrating only to visible apnoeas under-prescribes and the patient returns symptomatic. The second slip is forgetting supine REM as the acid test of the final pressure; examiners ask specifically which position-stage combination validates the titration, and that pair is the answer. Third, leaks: candidates escalate pressure through a night ruined by mask leak, scoring artefact as disease; the rule is refit first, interpret second. And the modern mark-earner: treatment-emergent central sleep apnoea — central events appearing as CPAP rises — recognised rather than buried. The Indian clinic angle: device downloads are standard follow-up even in smaller centres, and the viva expects "4 hours per night, residual AHI below 5".
Frequently asked questions
At what pressure does CPAP titration start and how is it raised?
Start at 5 cm H2O and increase in 1 cm H2O increments, each held at least about 5 minutes, until apnoeas, hypopnoeas, RERAs, snoring and flow limitation resolve.
Why must supine REM sleep validate the final CPAP pressure?
The upper airway is most collapsible in supine REM, so a pressure adequate in lighter, lateral N2 sleep commonly fails in that position-stage combination.
When is bilevel positive airway pressure preferred over CPAP?
When events persist at high CPAP (around 15 cm H2O or more), when pressure intolerance or aerophagia limits CPAP, or when hypoventilation needs ventilatory support.
What is treatment-emergent central sleep apnoea?
Central apnoeas appearing during CPAP titration, often at higher pressures — managed by pressure reassessment, range devices or bilevel with backup rate in selected patients.
What adherence targets define successful PAP therapy at follow-up?
Conventionally at least 4 hours of use per night on most nights, with residual AHI below 5 and acceptable leak, reviewed from device downloads.