When you are scheduled to undergo a sleep study, you may not realize that there is more than one kind of sleep study.
Aside from the home sleep apnea test (HSAT)—which you may have already experienced—there are three main in-lab, overnight sleep tests you might encounter.
Many people start with an overnight or nocturnal polysomnogram (NPSG), a baseline diagnostic test.
Others may already have an apnea diagnosis and return for a CPAP titration study, which involves starting the night using positive airway pressure (PAP) therapy.
A third test is a blend of both of these, the split night study.
What all sleep studies have in common
You prepare for all sleep studies in more or less the same fashion. You:
Follow the requests provided to you by your sleep center in terms of alcohol consumption, prescription medication use, meals, caffeine intake, etc.
Bring in completed paperwork that was sent to you ahead of time.
Pack the same items to all sleep studies (learn more about packing for a sleep study here).
Will be expected to do the same thing at every test: namely, sleep as best you can.
What is a split night sleep study?
When your sleep physician highly suspects that you have moderate to severe obstructive sleep apnea (OSA), they can write the order for a sleep technologist to conduct what is known as a "split night" study during your overnight polysomnogram.
How would they know to suspect this? Your sleep physician might have seen evidence of it on a prior HSAT, for instance, or you might carry several risk factors for sleep apnea that could predispose you to sleep breathing problems.
If this is the case, your sleep technologist will prepare you for an ordinary overnight test, but will be observing key data from your study in real time to determine whether you might meet prearranged criteria for treatment. These criteria are well established by the American Academy of Sleep Medicine (AASM), which delivers a standard protocol that credentialed sleep centers must follow.
When the sleep technologist identifies certain sleep-breathing episodes and markers after a specific time has passed during your study, they are then ordered by the sleep physician to initiate a trial of therapy using CPAP.
This is why it is called a "split night" study. It combines an ordinary NPSG with a CPAP titration, which occurs partially into the test, "splitting the night."
All of the sensors you are wearing stay put except for the airflow measurements, which the CPAP machine will measure once applied. You need not worry about any of this, however. The sleep technologist knows precisely what to do to prepare you for a split night study.
At the end of the night, after you've completed your test using CPAP, you are "unhooked." The test data your sleep technologist gathered is collected, then scored, reviewed, and interpreted later by your sleep physician, who will discuss the results with you at a separate visit. At that time, they will provide you with their therapy recommendations.
Your sleep technologist is not a medical doctor and cannot interpret your study results; do keep this in mind in the morning as you clean up. Many patients are curious about their study results, but it's outside the scope of a sleep technologist to discuss any of these particulars with you.
Keep in mind that, while your sleep technologist may have orders to start a split night protocol, you still must provide them with enough data to show the need for it. Some people have mild sleep apnea and do not qualify for a split night study because they do not meet the criteria for it.
How do I prepare for a split night study?
You don't have to do anything differently to prepare for this test except for this: you will need to sample a few minutes of CPAP therapy prior to your study. This usually takes place during "hookup," before your test starts.
To prepare for the switch from an ordinary overnight sleep test to a split night test, the sleep technologist will have you try on one or more CPAP masks to find the one you are most comfortable wearing.
This usually takes place prior to the application of test sensors so you can have a favorable first-time encounter with the mask.
Your sleep technologist will also have you try out positive airway pressure by having you place the mask on your face, then turning on the CPAP machine to the lowest setting. This is normally the same setting that your split night study begins with.
By doing this, you are given an opportunity to experience the feeling of using CPAP. You will likely try it while sitting up, and then again while reclined, so the sleep technologist can best adjust your mask.
This process makes it easier for both of you to make the transition later in the evening (should it occur) because the mask you choose will already be pre-fit to your face and, because you have already tried out the therapy before the test, you will not need to have a training session in the middle of the night. The sleep technologist simply enters your room, gently awakens you, and helps you on with your mask so you can begin therapy.
What happens if I can't fall asleep while wearing the CPAP mask?
Many patients who struggle to breathe find using CPAP in the middle of the night a relief, while others may need some time to adjust.
You might be anxious because you have been woken up in the middle of the night and are nervous about using the therapy. This is normal; your best approach is to relax and practice counting your breaths at a slow and steady pace.
By and large, the vast majority of patients, even if they experience some "first night effect," do fall asleep during a split night study and do provide the sleep technologist with adequate data for the sleep physician to interpret later.
Keep in mind that, during your split night study, especially at the beginning, your sleep technologist can and will adjust air pressure, humidity, and settings to improve your comfort. Once you're asleep, they'll continue to treat your upper airway obstructions as they arise throughout the test, ideally until they are resolved, remotely from their station the lab.
The advantages of a split night study
For moderate to severe apnea patients in a split night study, the urgency of their condition warrants starting therapy on the first night of a study so they can get the benefits of therapy immediately.
A split night study also allows your sleep technologist ample opportunity to identify your unique positive airway pressure settings in the same night, without requiring that you return for a second night to do so.
You can equally benefit from a split night study because it gives you a chance to try out several mask types or brands to find the perfect fit, which is so crucial to success using CPAP.
Ultimately, whatever sleep test you end up encountering, the goal is always the same: to identify your sleep disorder—whether it's related to breathing, movement, or other reasons—and get you started on appropriate therapy so you can find your way back to healthy, restorative sleep.