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Polysomnogram (PSG) is a multi-channel ("poly") recording ("gram") during sleep ("somno"). A doctor may order a polysomnogram because the patient has a complaint such as daytime fatigue or sleepiness that may be from interrupted sleep. Typically, doctors order a polysomnogram to diagnose or rule out obstructive sleep apnea. Although the PSG can be done during the day or night, the vast majority of sleep studies are done at night, when most people sleep. Shift workers and people with circadian rhythm sleep disorders can be accommodated in some labs by having the test at other times of day.For the standard test the patient comes to a sleep lab in the early evening, and over the next 1-2 hours is introduced to the setting and "wired up" so that multiple channels of data can be recorded when he/she falls asleep. The sleep lab may be in a hospital, a free-standing medical office, or in a hotel. A sleep technician should always be in attendance and is responsible for attaching the electrodes to the patient and monitoring the patient during the study.
Uses A polysomnogram usually records:
Example of summary report from overnight 'diagnostic' sleep study (PSG) Mr. J
-, age 41, 5’8” tall, 265 lbs., came to the sleep lab to rule out obstructive sleep apnea. He complains of some snoring and daytime sleepiness. His score on the Epworth Sleepiness Scale is elevated at 15 (out of possible 24 points), affirming excessive daytime sleepiness (normal is <10/24).This single-night diagnostic sleep study shows evidence for obstructive sleep apnea (OSA). For the full night his apnea+hypopnea index was elevated at 18.1 events/hr. (normal <5 events/hr; this is “moderate” OSA). While sleeping supine, his AHI was twice that, at 37.1 events/hr. He also had some oxygen desaturation; for 11% of sleep time his SaO2 was between 80% and 90%. Results of this study indicate Mr. J
would benefit from CPAP. To this end, I recommend that he return to the lab for a CPAP titration study. (Interpreted by Dr. M.)
'Split night' sleep studies The above report mentions CPAP as treatment for obstructive sleep apnea. CPAP is continuous positive airway pressure, and is delivered via a tight fitting mask to the patient's nose or nose & mouth (some masks cover one, some both). CPAP is typically prescribed after the diagnosis of OSA is made from a sleep study (i.e., after a PSG test). To determine the correct amount of pressure, the right mask size, and also to make sure the patient is tolerant of this therapy, a 'CPAP titration study' is recommended. This is the same as a 'PSG', but with the addition of the mask applied, so the technician can increase the airway pressure inside the mask as needed, until all (or most all) of the patient's airway obstructions are eliminated. The above report recommends Mr.J
return for a CPAP titration study, which means return to the lab for a 2nd all night PSG (this one with the mask applied). Often, however, when a patient manifests OSA in the first 2 or 3 hours of the intial PSG, the technician will interrupt the study and apply the mask right then and there; the patient is literally woken up and fitted for a mask. The rest of the sleep study is then a 'CPAP titration.' When both the diagnostic PSG and a CPAP titration are done the same night, the entire study is called 'Split Night'.The advantages of the split night study are: 1) the patient only has to come to the lab once, so it is less disruptive than coming two different nights; 2) it is 'half as expensive' to whomever is paying for the study. The disadvantages of a split night study are 1) less time to make a diagnosis of OSA (Medicare requires a minimum of 2 hours of diagnosis time before the mask can be applied); and 2) less time to assure an adequate CPAP titration. If the titration is begun with only a few hours of sleep left, the remaining time may not assure a proper CPAP titration, and the patient may still have to return to the lab. Because of costs, more and more studies for 'sleep apnea' are attempted as split night when there is early evidence for OSA. Note that both types of study - with and without a CPAP mask - are still polysomnograms. When the CPAP mask is worn, however, the flow measurement lead in the patient's nose is removed, and a wire coming directly from the mask then measures air flow.
Example of summary report from a 'split night' sleep study (PSG) Mr. B---, age 38, 6 ft. tall, 348 lbs., came to the Hospital Sleep Lab to diagnose or rule out obstructive sleep apnea. This polysomnogram consisted of overnight recording of left and right EOG, submental EMG, left and right anterior EMG, central and occipital EEG, EKG, airflow measurement, respiratory effort and pulse oximetry. The test was done without supplemental oxygen. His latency to sleep onset was slightly prolonged at 28.5 minutes. Sleep efficiency was
normal at 89.3% (413.5 minutes sleep time out of 463 minutes in bed). During the first 71 minutes of sleep Mr. B
manifested 83 obstructive apneas, 3 central apneas, 1 mixed apnea and 28 hypopneas, for an elevated apnea+hyponea index (AHI) of 97 events/hr. (= “severe” OSA). His lowest SaO2 during the pre-CPAP period was 72%. CPAP was then applied at 5 cm H2O, and sequentially titrated to a final pressure of 17 cm H2O. At this pressure his AHI was 4 events/hr. and the low SaO2 had increased to 89%. This final titration level occurred while he was in REM sleep. Mask used was a Respironics Classic nasal (medium-size).In summary, this split night study shows severe OSA in the pre-CPAP period, with definite improvement on high levels of CPAP. At 17 cm H2O his AHI was normal at 4 events/hr. and low SaO2 was 89%. Based on this split night study I recommend he start on nasal CPAP 17 cm H2O along with heated humidity. (Interpreted by Dr. M.)
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