What Are Clear Airway (CA) Apnea Events on My CPAP Machine?
If you've seen the term "CA" on your CPAP machine download, machine's display, or apps such as MyAir or DreamMapper, you might be scratching your head. What are these events? Are they dangerous? How are they diagnosed? Read on to find out answers to the above and more.
CPAP Machine Download Showing Elevated AHI with Predominantly CA (Central) Events.
The Meaning of CA
Your machine estimates how many residual breathing events that you have while using it. A CA means that your machine thinks that your airway was open but you forgot to breathe for at least 10 seconds. This is in contrast to an obstructive airway (OA) event. With an OA, the machine thinks that your throat was fully-closed for at least 10 seconds.
Are CAs the Same Thing As Central Apneas?
Essentially, they are the same. But central apneas can only technically be diagnosed with a sleep study.
How Does My PAP Machine Detect CAs?
PAP manufacturers have proprietary algorithms to estimate residual abnormal respiratory events. PAP machines need to be able to distinguish between OAs and CAs because OAs mean more pressure is needed while CAs mean that the pressure should not be increased and in some cases the pressure should be decreased as higher pressures can bring out central sleep apnea. Accurate detection of OAs and CAs is essential for the proper function of auto-titrating PAP machines.
Sleep clinicians believe that PAP machines estimate AHI by periodically sending a pulse of air down your airway. This pulse of air is too subtle for users to detect. If the air pulse bounces back, this tells the machine that the airway is closed and it will register in your data report for the night as an OA. If you're on an auto-PAP machine, it will increase the pressure in response to repetitive OAs. If the machine detects that the airway is open AND there is no effort to breathe (based on the pattern of airflow exiting the machine), it will register as a CA. In this situation, Auto-PAP machines should keep the pressure steady.
How Valid Are CA Numbers?
They are reasonably accurate. In my experience, PAP machines tend to underestimate the number of residual abnormal breathing events, both obstructive and central.
However, it's importantly to realize that you can artificially inflate CA numbers by doing deep breathing or breath-holding exercises while wearing your CPAP machine. The machine, of course, doesn't know if you're awake or asleep and any breath-holding spell will be logged as CAs.
Are CAs Dangerous?
Excessive CAs could indicate that your sleep apnea is not effectively treated. Suboptimally treated sleep apnea can keep you at risk for long-term medical problems like high blood pressure, heart disease, stroke, and dementia.
How Many Is Too Many?
Generally, an AHI >5 is a red flag. In my experience, if PAP is working really well the AHI should be <3. If the AHI is >5 and the majority of the events are CAs then it could indicate that your therapy needs to be adjusted. However, at lower numbers CAs could still be problematic - it all depends on your "clinical response" or how well you are sleeping and feeling during the day. Validated scales like the Epworth Sleepiness Score can help quantify if you have abnormally high levels of daytime sleepiness.
What Should I Do If I Have A Lot of CAs?
First, don't panic if it's just one night. Look for trends. If your CA index has consistently been high, make sure that your mask leak is in the acceptable range. High leak can cause your machine to ramp up the pressure in a compensatory response which can in turn cause more CAs.
If your CA index is chronically high and you're having any of the following symptoms, make an appointment with a sleep doctor:
- Not feeling great when you wake up despite getting at least 7-8 hours of sleep and using your PAP machine religiously
- Waking up gasping for air while using your PAP
- Your bedpartner hears you taking shallow breaths or having pauses in your breathing during PAP use
- Excessive daytime sleepiness or fatigue
Joseph Krainin, M.D., FAASM is the founder of Singular Sleep, the world's first online sleep center. He is a Fellow of the American Academy of Sleep Medicine and board-certified in both sleep medicine and neurology. He has been practicing medicine for over 10 years.