If you have been diagnosed with sleep apnea, you are probably prescribed continuous positive airway pressure, or CPAP, as the best possible treatment. However, what most people wonder whether the severity of sleep apnea measured by the AHI is compatible with the needed CPAP pressure. So, we decided to discuss how CPAP settings are related to the severity of sleep apnea. Additionally, we will talk about the additional factors which can be involved in determining the optional treatment.
Sleep Apnea Severity and CPAP Pressure
One would assume there is a close relationship between the degree of obstructive sleep apnea and the prescribed CPAP pressure setting. However, this connection isn’t so direct when treating sleep apnea.
In order to diagnose obstructive sleep apnea, a patient has to undergo an overnight sleep study or home sleep apnea test. These tests determine the number of times per hour of sleep that the upper airway collapses, which results in a drop of blood oxygen levels or awakenings from sleep. So, if the airway completely collapses this is called apnea and the total number of these events per hour of sleep is known as the apnea-hypopnea index (AHI).
The Apnea-Hypoxia Index
The apnea-hypopnea index is, in fact, a general classification of the severity of sleep apnea. Hence, it is considered normal when there are fewer than 5 events per hour. However, a patient has mild obstructive sleep apnea if 5 to 15 events per hour are recorded. More than 15 but fewer than 30 events recorded indicate that a person has moderate OSA, while over 30 events per hour of sleep show that the person experiences severe obstructive sleep apnea.
What most people think is that the more severe sleep apnea is, the higher CPAP pressure setting will be required. However, this doesn’t always seem to be the case. Most of the times, the treatment starts at a low setting and gradually increases.
The lowest setting on CPAP machines may be 4 to 5 centimeters of water pressure (CWP), while the maximum setting varies, but it’s usually 25 or 30 CWP.
How to Determine the Required CPAP Pressure to Resolve Sleep Apnea
When the CPAP pressure setting is determined as part of an overnight study, the polysomnography technologist will observe the process and adjust the setting while you sleep. The main aim is to eliminate sleep apnea and snoring. It is also important to optimize the setting while you sleep on your back, a position which makes sleep apnea worse.
However, many people opt for a self-adjusting CPAP machine, known as Auto CPAP or APAP. When this is the case, the prescribing physician allows a range of pressures. This means that the pressure will start at a low level and adjust as needed in response to measured airway resistance.
Nevertheless, the severity of sleep apnea doesn’t directly correlate to the required CPAP pressure. That means that people with severe OSA can need relatively modest pressures, while people with mild OSA can need high pressures. People with severe sleep apnea require higher pressures on CPAP or even bilevel therapy.
Additional Factors Which Can Affect the CPAP Pressure Setting
There are a number of additional factors which can affect determining the required CPAP pressure setting, including the nature of the airway obstruction and the anatomy of the upper airway. Additionally, obesity and being overweight can also affect the setting, as well as, medications that relax airway muscles, alcohol use, and sleeping on your back.
Proper Setting May Depend on Review of the Residual AHI
So, from everything we mentioned so far, determining the CPAP pressure setting which is needed to treat your sleep apnea is not an easy job. This pressure setting might vary while you sleep. So, your sleep apnea won’t be controlled if the pressure is too low, while high pressure can lead to mask leak or air swallowing.
Therefore, it is crucial to consult a sleep specialist who will set the machine properly and ensure the greatest benefits. So, it might be better to use an Auto CPAP machine that is able to adjust to these other variables.