What Is the Goal AHI for CPAP Treatment of Sleep Apnea?
Continuous positive airway pressure (CPAP) is commonly prescribed to treat sleep apnea, a condition diagnosed via a sleep study. The goal is to improve breathing at night, but how do you know if treatment such as the CPAP is working well enough? The apnea-hypopnea index (AHI) can be a helpful measure to diagnose the severity of the condition at baseline and track the effectiveness of your treatment.
What does the AHI reading mean on a sleep study or CPAP machine? What is considered an event? If the AHI number is elevated, you may ask, “How do I adjust my CPAP machine?”
Learn what your goal AHI should be to maximize the benefits of using CPAP for optimal therapy and how the pressures are determined and should be adjusted.
What Is AHI?
First, it is important to understand what the apnea-hypopnea index (AHI) reading means, both with sleep studies and on a CPAP machine.
This measurement is often presented within the context of a sleep studyreport. It is the number of times per hour of sleep that your upper airway (tongue or soft palate at the throat) partially or completely collapses, leading to a brief arousal or awakening from sleep or a drop in blood oxygen levels.
The partial collapse of the airway is called a hypopnea.
The complete absence of airflow through the nose and mouth, despite an effort to breathe as measured at the chest and abdomen, is called an apnea event.
The AHI is used to classify the severity of sleep apnea. This same classification is used to assess how well treatment, such as the CPAP machine, is working.
The following guidelines are used in adults:
Normal: Fewer than 5 breathing events per hour of sleep
Mild sleep apnea: 5 to 14.9 breathing events per hour of sleep
Moderate sleep apnea: 15 to 29.9 breathing events per hour of sleep
Severe sleep apnea: 30 or more breathing events per hour of sleep
Children’s sleep is analyzed with stricter criteria and more than one event per hour of sleep is considered to be abnormal.
AHI Measurement in a Sleep Study
A sleep study (polysomnogram) is performed in a sleep disorder center and is typically used to diagnose sleep apnea. It is also possible for the condition to be diagnosed based on home sleep apnea testing.
A lot of information is collected, and part of the purpose of these studies consists of tracking your breathing patterns through the night. This is accomplished with several sensors:
Nasal oxygen cannula (or thermistor) with plastic prongs that sit in the nostrils
Respiratory effort belts that stretch across the chest and/or stomach
An oximeter clip that measures continuous oxygen and pulse rate by shining a laser light through a fingertip
All of this information is analyzed to determine how many times you breathe shallowly or stop breathing altogether during the night. Any partial obstruction of the airway is called a hypopnea. Hypopnea refers to a transient reduction of airflow (often while asleep) that lasts for at least 10 seconds. Shallow breathing or an abnormally low respiratory rate may be called hypoventilation.
A complete cessation in breathing is called apnea (from the Greek meaning “no breath”). Hypopnea is less severe than apnea (which is a more complete loss of airflow). It may likewise result in a decreased amount of air movement into the lungs and can cause oxygen levels in the blood to drop. Sleep apnea is more commonly due to partial obstruction of the upper airway.
In order to count in the AHI these pauses in breathing must last for 10 seconds and be associated with a decrease in the oxygen levels of the blood or cause an awakening called an arousal. These awakenings may fragment sleep, make it unrefreshing, and lead to daytime sleepiness.
There are some sleep facilities that use other measures to assess this degree of severity. The respiratory-disturbance index (RDI) may be used if a measurement of airway resistance with a pressure esophageal manometer is also included in the study. The oxygen-desaturation index (ODI) attempts to calculate the number of apnea or hypopnea events per hour that lead to an oxygen drop of at least 3 percent. This is thought to be important in assessing the risk of long-term cardiovascular (high blood pressure, heart attack, and heart failure) or neurocognitive (stroke and dementia) consequences.
If your sleep study does not contain these more specific measures, this is nothing to worry about.
Goal AHI to Optimize CPAP Therapy
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“Alaska Sleep Clinic has a history of providing the most comprehensive sleep medicine services in the state of Alaska. Its potential has only begun. I am here to take these high-quality, comprehensive services to all Alaskans.”
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Brent Fisher has held leadership positions spanning a wide variety of complex and start-up organizations: manufacturing (pharmaceutical & medical device), software development, hospitals (academic and community), medical groups, consulting, hospice, military, engineered devices, engineered plastics, and private equity.
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His writings have been published in various magazines, trade journals, and medical journals, including the Physician Executive Journal, Healthcare Executive, Modern Healthcare, Group Practice Journal, New England Journal of Medicine, and Journal of Healthcare Management (Best Article Award).
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