How to Set the Pressure of a CPAP Machine
CPAP Settings: Why and How They Are Determined
The majority of people who test positive for sleep apnea on their sleep apnea test will pursue CPAP therapy, which is the gold-standard treatment for the disorder. It is critically important to find the proper pressure settings to fix the individual's case of sleep apnea.
Why Is It Necessary to Have the Correct CPAP Pressure Settings?
Improperly treated sleep apnea can lead to both residual symptoms like poor quality sleep and daytime sleepiness as well as long-term medical consequences such as high blood pressure, heart disease, and stroke. The oxygen drops associated with sleep apnea seem to be the main driver for the most dangerous medical repercussions of sleep apnea so it is key that the CPAP machine's settings keep the oxygen levels in the safe zone (90% or higher).
How Are CPAP Machine Settings Determined?
The goal of setting a CPAP machine is to find the lowest effective pressure to keep your airway open in all body positions and all stages of sleep. There are two ways to determine this pressure:
In-Lab PAP Titration Study
In-lab PAP titrations are performed in sleep labs. You will have electrodes hooked up all over your body just as you would for a diagnostic sleep study. During the study, the sleep technologist will "titrate" or adjust the pressure while monitoring you in another room. Typically, you will start out on a CPAP machine. The ultimate goal is to find the lowest pressure that keeps your airway open for at least 15 minutes while you are in "REM-supine" sleep, i.e., you're sleeping on your back and in the rapid eye movement stage of sleep. This condition is considered the worst for your airway. Sometimes that is just not possible to achieve; the general goals are to achieve an AHI at least <5/hour, no oxygen desaturations <90%, and an average oxygen saturation of at least 93%. The technologist will try various pressures, searching for the optimal one.
Bad things that can happen during the titration:
- Central sleep apnea (CSA): sometimes starting CPAP cause the body to "forget" to breathe, which is called central sleep apnea. Sometimes this is a sign of getting too much pressure. Other times, CSA was there from the start but only becomes apparent after the airway is opened up. Both of these cases are typically referred to as "complex sleep apnea." When this happens, the technologist will usually back off the pressure and try to slowly increase it again. If this is ineffective, a more advanced type of PAP such as BiPAP or ASV will be initiated.
Central sleep apnea - the THO (thoracic belt) signal is absent, indicating that the belt around the chest is not detecting any effort to breathe
- Persistent hypoxemia. If the baseline oxygen saturation remains low despite effectively opening up the airway, the patient will either need to be switched to BiPAP or started on supplemental oxygen.
After the In-Lab Titration
Your sleep study will be reviewed by a sleep doctor who will write a report indicating the most effective PAP modality (CPAP, BiPAP, or ASV with or without supplemental oxygen) and pressure settings. You will need to obtain a prescription from your sleep doctor or whomever ordered the sleep study to obtain the equipment. This prescription will be fulfilled by a durable medical equipment company.
Home Auto-PAP Titrations
In this scenario, which is increasingly common, the patient does not have an in-lab PAP titration but is given an auto-titrating PAP machine, usually an auto-CPAP (APAP) to start. The machine will be initially set to a "wide" range of pressures. I typically favor giving the entire range of pressures in the beginning, i.e., 4-20 cwp but I have seen some clinicians give ranges like 5-15 cwp.
The goal for auto-PAP titrations is the same as in-lab PAP titrations. This is how it is typically achieved:
- Let the patient use the wide range of pressures for a limited period of time.
- Assess the pressure that has been found to keep the airway open 90% of the night (P90) or 95% of the night (P95%) - this varies by manufacturer - and change the machine to this setting. I typically do not cap the pressure but let the machine range as high as it needs to go above the P90/95 but some practitioners will but them on a fixed pressure and others will have a more limited range. Monitoring the data in the initial stages of therapy will also indicate if complex sleep apnea has reared its ugly head. Modern CPAP machines are so sophisticated that, not only do they determine fairly accurately how many residual breathing events you are having per hour, they can differentiate obstructive from central breathing events. I typically like at least 2-3 weeks of good data before titrating the machine. In the download below, you can see an example of the P95% pressure setting from the patient's ResMed BiPAP machine indicating 12.2/7.2 cwp. I then remotely changed this patient's machine to 12/7-25/20 cwp.
- Auto-PAP machines are not able to monitor and adjust based on oxygen levels so to verify that oxygen levels have been fixed, an overnight pulse oximetry study is needed. In my experience, about 25% of the time, the oxygen levels will be improved from the baseline sleep study but still not in the desired range and a second adjustment may be indicated.
This initial oxygen level study was from a patient who was "lost to follow up" and never had the machine adjusted for him. Note the "saw-tooth" pattern of oxygen drops during the first half of the study, indicative of ongoing sleep apnea. He dropped to a low of 84% despite using his CPAP machine:
The patient re-established care with us. After enrolling in our monitoring program, we gathered several weeks of data and then adjusted his machine to the P95 pressure. His oxygen levels were dramatically improved:
I made another slight pressure adjustment after this to get him above 90% all night long. Clinically, he is doing great: he reports excellent sleep quality and he has been able to stop taking his blood pressure medication.
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.
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