Central vs Obstructive Apnea: What 'Clear Airway' (CA) Events Mean

If you've opened your CPAP report and spotted events labeled "CA" or "Clear Airway," you've found one of the most misunderstood numbers in sleep therapy. These are central apneas, and they behave very differently from the obstructive events your CPAP was prescribed to treat. Knowing the difference helps you read your data accurately and — when something shifts — bring the right question to your sleep clinician.

What 'clear airway' (CA) means on your report

A clear-airway (CA) event is your machine's term for a central apnea: a pause in breathing of at least 10 seconds during which your airway is open but you make no respiratory effort. Your brain briefly fails to send the "take a breath" signal, so the chest and diaphragm go still even though nothing is physically blocking the airway.

Different manufacturers label this the same idea with different words:

The word "clear" is the key. Your CPAP detects whether the airway is open by sending a tiny test pulse during a pause; if air moves freely, the airway is "clear," and the machine concludes the cause is central rather than obstructive. (For a side-by-side of every code on your report, see CPAP Event Types Decoded.)

It's normal to log a handful of central events some nights — brief centrals can occur at sleep onset or after a position change in healthy sleepers. A few scattered CAs are usually noise, not a trend. What matters is the pattern over weeks, which we'll come back to.

How CA differs from obstructive apnea

Both event types stop airflow for 10+ seconds, but the mechanism is opposite — and that's why the treatment story is different.

• Obstructive apnea (OA): The airway physically collapses or is blocked. You keep trying to breathe — chest and belly strain against a closed throat — but no air moves. This is the classic mechanical problem CPAP was built to solve.
• Central apnea (CA / clear airway): The airway is open, but the drive to breathe pauses. There's no effort to detect because the signal never arrived.

A simple way to hold the two apart:

A third category, mixed apnea, starts central and ends obstructive (or the reverse). For the full three-way breakdown, see Obstructive vs Central vs Mixed Sleep Apnea and the broader Understanding Sleep Apnea pillar.

One caveat worth knowing: home machines estimate event types from airflow and a forced-oscillation pulse — they don't measure brain waves or chest effort the way an in-lab study does. So device-reported CA counts are good for spotting trends, but a formal central-apnea diagnosis still belongs to a sleep study with effort belts and EEG. (More on that distinction in In-Lab PSG vs Home Test.)

What CPAP can and can't do for central events

Here's the part that trips up many users. CPAP is designed to splint the airway open — it pushes a column of pressurized air down the throat to keep soft tissue from collapsing. That's exactly the right tool for obstructive events, and it reliably resolves them.

But a clear-airway event isn't a collapse problem. Pressure can't manufacture the missing signal to breathe, so CPAP does not directly correct the unstable breathing drive behind central events. Splinting an already-open airway does nothing for a pause that has no obstruction to fix.

And critically: raising your pressure does not fix central apneas — and higher pressure can sometimes provoke more of them. This is why chasing a rising CA number by turning the machine up is the wrong move. It's also one of several reasons we never walk readers through self-adjusting prescribed pressure (see Can I Adjust My Own CPAP Pressure?).

This doesn't mean CPAP is useless when centrals appear. As you'll see next, continued CPAP under clinician guidance is often part of the solution — just not by adding pressure.

When rising CA events matter

The signal to watch isn't a single night — it's a sustained, climbing trend in your clear-airway count, especially if it's a new pattern. A specific scenario has a name: treatment-emergent central sleep apnea (TECSA), also called complex sleep apnea. This is when your obstructive events resolve nicely on CPAP, but central events emerge or persist on therapy.

A few facts that put TECSA in perspective:

• It appears in roughly 5–15% of PAP titrations — uncommon, but far from rare.
• In about 60–80% of cases it resolves on its own within weeks to a few months of continued CPAP use.
• The usual first step is watchful waiting on CPAP under clinician guidance — not more pressure, and not stopping therapy.
• Persistent cases may warrant a switch to BiPAP or ASV (adaptive servo-ventilation), added oxygen, or other measures your clinician selects.

So a temporary bump in centrals during your first weeks of therapy is often part of the body adjusting. What deserves a closer look is when CA events stay elevated, or climb, alongside any of these:

• Returning daytime sleepiness or symptoms you thought CPAP had fixed
• Deep oxygen drops at night
• New medications — opioids are a classic central-apnea trigger
• New or worsening heart or kidney conditions
• A breathing rhythm that waxes and wanes in a repeating crescendo-decrescendo pattern, which can point toward periodic breathing or Cheyne-Stokes respiration (see Periodic Breathing & Cheyne-Stokes on Your CPAP Chart and the heart connection)

For a deeper dive on this exact scenario, our companion guide Central Apneas Showing Up on CPAP: Treatment-Emergent CSA Explained walks through what to track and what to expect.

Where your residual AHI fits

The widely used benchmark for effective CPAP therapy is a residual AHI below 5 events per hour — the AASM defines an "optimal" titration as reducing AHI under 5, which is also the normal, non-apneic range. Some clinicians aim lower when it's comfortably achievable, but there's no formal guideline establishing "below 2" as a target, and goals are individualized with your provider. (More on what counts as good in What Is a Good AHI on CPAP?.)

The number that matters here isn't just whether your AHI is under 5 — it's what it's made of. An AHI of 4 that's almost entirely clear-airway events is a different conversation than an AHI of 4 that's mostly obstructive, because CPAP can't address the central portion the same way. This is exactly where seeing your data broken down pays off. SomniCharts splits your AHI into obstructive versus clear-airway events automatically and in plain language — across ResMed, Philips Respironics (including the encrypted DreamStation 2), and Löwenstein prisma data — so you can see at a glance whether your residual events are the kind CPAP can't fix, and carry that breakdown straight to your provider.

The clinician conversation (do not self-adjust)

If your clear-airway events are trending up, the right response is to use your data to start an informed conversation with your sleep clinician — not to change settings yourself. Central apnea is a breathing-control issue that can intersect with medications, heart and kidney health, and the very pressure your machine delivers; sorting that out is a clinical job.

Bring concrete evidence rather than a single bad night. A useful packet looks like:

1. Your CA trend over several weeks, not one night — single-night swings are mostly noise (see Why Does My AHI Change Night to Night?).
2. The obstructive-vs-central split of your residual AHI, so your clinician can see what CPAP is and isn't handling.
3. Your leak data, because high leak can distort and under-report event counts (more in What's an Acceptable CPAP Leak Rate).
4. Any recent changes — new medications (especially opioids), new heart or kidney diagnoses, or returning symptoms.

What not to do: don't raise your pressure to push the central number down. It doesn't work, and it can make centrals worse. The defensible, effective path is the same one your prescription assumes — read your data, watch the trend, and let your clinician decide whether watchful waiting on CPAP, a switch to BiPAP/ASV, or further testing is the right next step.

Clear-airway events aren't a sign you're "doing CPAP wrong." They're a different kind of breathing pause that your machine is honest enough to flag — and a well-organized look at the trend is the most useful thing you can put in front of your doctor.