If you recently had or ordered a sleep study to test for sleep apnea, the question foremost in your mind is probably what your results have to say about your sleep health or the health of your patient.
However, unless you know what to look for, your sleep study report may seem more perplexing than informational.
Here are six things you need to know in order to be able to read and understand a sleep study report.
Note: You should review your results with your physician and discuss your diagnosis, next steps and treatment options.
1. The first number you should look for: the AHI or RDI
Also known as the apnea/hypopnea index, this statistic is the definitive metric in determining if a patient suffers from sleep apnea. It counts the average number of apneas and hypopneas—in other words, respiratory events that cause a significant decrease in airflow— that the patient experiences per hour.
A quick look at this number can give you an idea of where you or your patient falls on a scale of sleep apnea severity.
2. Other sleep disruptions: arousals, leg movements
It’s called sleep apnea for a reason, right? In fact, it turns out that this name is a very limited picture of respiratory and brain-related events that can disrupt a patient’s sleep.
Many different events can be of concern. Apneas are probably the most well-known characteristic of this sleep disorder; they occur when a patient’s breath stops completely for at least ten seconds. But a hypopnea, a partial cessation of airflow, can be just as serious. There are also RERAs (respiratory effort related arousals) that can disrupt the breath or depth of sleep without qualifying as either of the two above events. Furthermore, the sleep study should pick up on any arousals (partial awakenings) or excessive movements of the legs. All of these factors should be taken into account when assessing sleep quality and considering treatment options.
Learn more about apneas, hypopneas and arousals here.
3. Sleep stages
During the night, humans progress through several sleep stages, known as N1, N2, N3, and REM sleep.
Adults typically cycle through the stages in that order multiple times per night. However, certain sleep disorders can disrupt and fragment this cycle, making it impossible for patients to achieve normal, revitalizing rest. For instance, sleep apnea can result in arousals that prevent people from ever sinking into the deepest stage of sleep that they need to feel recharged in the morning.
During the sleep study, brain monitors will keep track of which stage of sleep you are experiencing and will allow technicians to observe any irregularities.
For some people, sleep apnea is worse during REM sleep. A 2012 study in the Journal of Clinical Sleep Medicine analyzed 300 sleep studies and found that half of patients had a 2x increase in AHI while in REM sleep.
4. Body position
Similar to sleep stages, body position can also impact the severity of sleep apnea. The same 2012 Journal of Clinical Sleep Medicine study that analyzed 300 sleep studies found that 60% of patients had a 2x increase in AHI while sleeping on their backs. This is why the sleep technician will try to get each patient to sleep on his/her back for at least a portion of the sleep study.
The sleep study should show how much of your sleep time was spent on your right side, left side, prone (on your stomach) and supine (on your back).
5. Oxygen desaturation (SaO2)
If you stop breathing repeatedly during sleep, you’re not getting the amount of oxygen into your bloodstream that you need. Your oxygen saturation (SaO2) measures the percentage your body’s oxygen capacity that is actually being inhaled. In people with very severe sleep apnea, their oxygen levels can fall as low as 60% of ideal or lower during sleep—meaning that they are absorbing slightly over half the oxygen they need to function.
If your saturation dips anywhere below 95%, your brain and body are not getting enough oxygen. This can cause brain damage and serious cardiovascular problems. Fortunately, you can ensure you are getting the airflow you need by using a PAP (positive airway pressure) device, which will restore you to normal breathing and a good night’s sleep.
Check out this post to learn more about how oxygen saturation is measured during a sleep study.
6. Recommended therapy or next steps
Depending on the findings of your sleep study, the interpreting physician may recommend another sleep study or CPAP therapy. Here are a few examples of the most common next steps after completing a sleep study (learn more about the different types of sleep studies here):
- If you had a baseline PSG only which showed sleep apnea, you may need to return for a CPAP titration.
- If your CPAP titration was not complete, you may need to return for another CPAP titration or a bi-level titration (learn more about the different types of PAP devices here).
- If you had a successful CPAP titration, you may need to schedule a CPAP set-up.
- If you had a home sleep apnea test (HST) you may need to have an in-center study, titration or autoPAP titration at home.
- If your doctor suspects narcolepsy, you may need to return for a PSG & MSLT.
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Editor’s Note: This post was originally published in November 2015 and has been edited and updated for accuracy and comprehensiveness.