Why do I have to come back to the sleep lab!?

March 27, 2017

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Well, by this time someone thought you might have sleep apnea and sent you to the sleep lab. You put on all the wires, belts, cannulas and probes– making you fell like neo waking up (matrix reference). So somehow you managed to sleep but now they are telling you that you have to return for another sleep study!?!? Well although you might think people are out for you money, there is actually a very good reason why you might have to come back.

Before we get into it further, all you need to know is that there are 3 severities of sleep apnea: mild, moderate and severe. Severity is measured by the apnea-hypopnea index (AHI). AHI less than 5 equals no sleep apnea 5-14 equals mild; 5-29 equals moderate; Above 30 equals severe sleep apnea.

OK, with that out of the way what you need to know is that there are really 2 broad types of sleep studies. Home sleep studies and attended sleep studies (AKA polysomnogram or PSG). If you are at a point where you have never had a sleep study, it may be beneficial to ask your doctor about home sleep apnea testing (HSAT). Home sleep apnea test (as the name implies) can be done at home and is less expensive. It is less intrusive and has less input signals. An HSAT has, usually, 4 signals: oxygen sensor, heart rate, respiratory rate and flow sensor through the nose. A doctor will then interpret this information. In order to have an HSAT you have to carry a high likelihood of having obstructive sleep apnea (OSA). If you only snore occasionally or really have a small chance of having OSA, HSAT is not a good test for you.

For everyone else there is PSG.

There are three types of PSGs. First is the baseline PSG. This is the most common type. On this test you will come in, get hooked up, and sleep as much as you can—-not easy, I know. Now if you are having occasional apneas and score less than a 14 AHI total then most likely the test will continue until morning hits. The baseline PSG is over. The test is scored by your doctor and he/she recommends CPAP so then you have to come back for test #2 which is a titration study.

A titration study is the same as above but with positive airway pressure, usually CPAP. As the night ticks away, the sleep technician will adjust the pressures. They usually start at 5 cmH20 and increase to eliminate snoring. You can compare this to going to the eye doctor to get the exact prescription for you eye glasses. Optimally by the end of the night we have the exact pressure needed to stop you apneas. Now, this is still the gold standard of getting started on PAP therapy. There is something called APAP however which will obviate the need for a titration study.

The last type of study is the split night. Split night sleep study is the combination of both a baseline and a titration study. The main difference here is that the study is started as a baseline. As the test continues it is very evident that the person is having bad sleep apnea. Usually their AHI will be above 20. At this time the study stops, and is switched (or “split”) into a titration study. For the remainder of the night, the sleep technician tries to adjust the pressure to each specific patient. The only caveat to this is that now you have less time to arrive at a perfect pressure.

TL;DR

Now a days you can have a home sleep study or attended sleep study. Home sleep studies are for people with a high pretest probability of having sleep apnea. An attended PSG is where you have to come into the lab. You can have a baseline study which measures your apneas all night, A titration study is when you are started on positive airway pressure (aka CPAP), or a split night which is the combination of these two.

All caught up? I know it seems a bit confusing but the goal is to get you on CPAP (if needed) with the correct pressure. Do you have to come back? Well not always. Sometimes you can defer to start APAP which will automatically “guess” your pressure. APAP is usually for people who do not have many comorbidities. The standard of care is still to come back to make sure you are on the correct pressure.