Posted by sleepsurgeon on July 16, 2009 at 08:28:58:In Reply to: Re: Comments posted by biam2009 on July 16, 2009 at 00:51:01:
RDI (sleep study results) certainly is compared and every sleep specialist does it because it is really the only objective test we have. However, in comparing the results, one must keep the following in mind. I know all the patients focus on the RDIs. I have resisted in going over this particular issue because I did not want to make things more confusing for people. But I guess people need to know. The following disucssin is really not commonly known for the majority of the surgeons.
First, sleep study is just a snap shot of the overall sleep. There can be up to 30% night to night variability in the sleep study results because we don't always have the same sleep every night.
Second, although it is an "objective" test, it is extremely subjective. The test is scored by a technician and interpreted by a sleep physician. Every lab is different and every technician is different and most importantly, every sleep physician is different. The testing equipment is different between each labs-some more sensitivity than others. The major issue is the sleep physician's interpretation. The apnea scoring is pretty easy and is uniformally accepted, but the hypopnea is a real problem and a controversial issue in sleep medicine. The definition of a hypopnea is 30% reduction of air flow with a 4% reduction of oxygen saturation. The problem is that less flow restriction can still cause sleep arousals, thus many sleep physicians counts flow limitations which do not qualify as hypopneas. I am certainly not saying this is wrong but hence the problem in comparing studies. Some sleep physicians will score lots of hypopneas while others very little. You can have a study from the same lab where one physician will read it as mild but another will read it as moderate or evern severe, depending on how the hypopnea is counted. How do we count shallow air flow lasting 20 seconds as comparing to continuous shallow air flow lasting minutes the same or do we count them at all? This really is the biggest problem with comparing sleep studies. But it is all we got.
Again, a sleep study is a good diagnostic test but needs to be correlated with clinical symptoms. The fact is that you still have symptoms and the same RDI after surgery certainly makes people discouraged.
At the end of the day, this is really an academic point that people should know. The most important thing is that when patients are still tired and fatigued, they need help, especially when the sleep study still show sleep apnea.
- Re: Comments theDreamer 13:56 7/16/09 (1)
- Re: Comments sleepsurgeon 07:07 7/18/09 (0)