"please keep me updated about oximeters "
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Is AHI a good measurement unit?
There are (only) 3 things there is international consensus about when we talk Sleep Apnea.
1. AHI (Apnea Hypopneas events > 10 seconds per hour)
2. SaO2 Desaturations.
3. The full PSG study as the "Gold Standard".
Furthermore, there is international consensus on an AHI scale of severity:
Mild SA = AHI between 5 and 15
Moderate SA = AHI between 15 and 30
Severe SA = AHI > 30
Of course I agree that AHI is a good measuring unit to detect SA. But as with previous measurement of Nocturnal pulse oximetry, I believe that this unit has several shortcomings.
After this measurement unit was introduced, we have got a lot of new knowledge, e.g. about UARS. Most of PSG studies cannot measure this.
Even when we discuss the severity of SA, I am not sure this unit is good. For example, a person with severe SA can have very little or no desaturations, and conversely, a person with very mild SA can have strong desaturations. Corresponding with symptoms. I have also seen new studies that indicate that even AHI <5 can bring severe sleep problems.
I therefore think it is pointless to talk about the severity associated with AHI. I don’t know who and how this scale has been decided, but it is certainly comfortable among some doctors because they can use it for the preparation of guidelines and I have even seen that this scale is used in a simple decision table to determine the severity and the treatment of SA (or maybe the lack of treatment).
IMO There is too much focus on the AHI as the sole determinant of the severity of SA, from Sleep centers, Public health care systems and maybe especially Insurance companies.
I think that we need to look more at the whole person, and all of the symptoms until we have a better measuring unit.
Let me hear your opinion.
Henning
1. AHI (Apnea Hypopneas events > 10 seconds per hour)
2. SaO2 Desaturations.
3. The full PSG study as the "Gold Standard".
Furthermore, there is international consensus on an AHI scale of severity:
Mild SA = AHI between 5 and 15
Moderate SA = AHI between 15 and 30
Severe SA = AHI > 30
Of course I agree that AHI is a good measuring unit to detect SA. But as with previous measurement of Nocturnal pulse oximetry, I believe that this unit has several shortcomings.
After this measurement unit was introduced, we have got a lot of new knowledge, e.g. about UARS. Most of PSG studies cannot measure this.
Even when we discuss the severity of SA, I am not sure this unit is good. For example, a person with severe SA can have very little or no desaturations, and conversely, a person with very mild SA can have strong desaturations. Corresponding with symptoms. I have also seen new studies that indicate that even AHI <5 can bring severe sleep problems.
I therefore think it is pointless to talk about the severity associated with AHI. I don’t know who and how this scale has been decided, but it is certainly comfortable among some doctors because they can use it for the preparation of guidelines and I have even seen that this scale is used in a simple decision table to determine the severity and the treatment of SA (or maybe the lack of treatment).
IMO There is too much focus on the AHI as the sole determinant of the severity of SA, from Sleep centers, Public health care systems and maybe especially Insurance companies.
I think that we need to look more at the whole person, and all of the symptoms until we have a better measuring unit.
Let me hear your opinion.
Henning
Views: 3490
Replies to This Discussion
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Permalink Reply by RichM on
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I just changed over to a BiPap this past month it is a Auto M series I got it off the machine. I am still trying to get my full report from my last sleep study. He was an extended sleep study to also check for seizers. I dont get much sleep each night since my accident 2 years ago I get appox 2-3 hrs but not constant. my past week was 61.9. I have not notice much leaking. what would be a normal leak rate per min ?
Daniel Levy said:You need to clarify. By mentioning a 30-day average, I assume that you are reading information from the display on a Respironics CPAP/Auto or BiPAP. If the display says your AHI is 68.1 while using your device, it means either: a) You have very severe sleep apnea even with PAP therapy, or B) Something is very amiss with your pressure settings, mask fit, or the device itself. My gut says B, and if that's the case, you should head to your provider immediately to figure out what's going on.
If your AHI was 68.1 for your diagnostic sleep study, than you do indeed have very severe sleep apnea. Basically, your breathing is disturbing your sleep more than once a minute. If you think you're severe, at SomniHealth, I have a patient whose AHI was 145 events per hour! After two weeks with her CPAP, her AHI registered 6 on her device. More important than that was the vitality I could see in her. She gave me a big hug and told me that I had given her life back to her. For two year's now, she's been SomniHealth's "Poster Girl"
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Permalink Reply by Daniel on
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Leak rate is very difficult to interpret with Respironics devices, since the device does not distinguish between intentional leak (the exhaust port) and unintentional leak (mouth breathing or poor mask fit). An acceptable leak rate is a function of both the pressure settings and the type of mask you are using. A very rough rule of thumb is about 50 Liters per minute. If the leak rate is higher than that, you should have someone who can download and interpret the detailed data from the seven most recent sessions help you to figure out if the problem is the mask, mouth-breathing, or body position-related.
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Dan, it was 41 so I take it that might not be the problem with having a 61.9 AHI for the past week
Daniel Levy said:Leak rate is very difficult to interpret with Respironics devices, since the device does not distinguish between intentional leak (the exhaust port) and unintentional leak (mouth breathing or poor mask fit). An acceptable leak rate is a function of both the pressure settings and the type of mask you are using. A very rough rule of thumb is about 50 Liters per minute. If the leak rate is higher than that, you should have someone who can download and interpret the detailed data from the seven most recent sessions help you to figure out if the problem is the mask, mouth-breathing, or body position-related.
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Permalink Reply by Judy on
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You can get a rough idea by finding the table chart in your mask's literature for the intentional or allowed vent rate for your mask at your set pressure and subtracting that figure from your reported leak rate. That table chart isn't the clearest piece of literature you will ever look at but its close enough to give you a good rough guess-timate.
With a Resmed device and a Resmed mask the device does the Leak calculation for you (assuming it is set to the correct Mask Selection setting). HOWEVER, if you use a non-Resmed mask then you should use the Standard mask selection setting. In the Standard setting the Resmeds have automatically subtracted 0.4 L/s (24 L/M) from the reported leak rate so you must ADD that 0.4 L/s or 24 L/M to the reported leak rate and compare that to the allowed vent rate at your setting in your mask literature.
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Permalink Reply by Henning on
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Hi Daniel,
I've thought about it for a while. As I see it, it is important to select the right sleep center, and the right sleep doctor.
In another discussion, I have read that Judy mentioned that the patient often not have a subsequent interview with the sleep physician. This may mean that other factors are not involved in the diagnosis.
Currently I am waiting for a new sleep study (a full PSG study). I have chosen the most professional sleep center in the country. And although we have a treatment guarantee of one month, then it is such that some sleep centers have a waiting list. So I opted to wait 3 months at a sleep study in this case.
Henning
Daniel Levy said:In cases where AHI is less than 15, Medicare has specified certain instances wherein beneficiaries may still qualify. The provider must have documentation on file from the prescribing physician stating one or more of the following:
- Excessive Daytime Sleepiness
- Impaired Cognition
- Insomnia
- Mood Disorders
- Hypertension
- Ischemic Heart Disease
- History of Stroke
Most private insurance companies also adhere to these guidellines, although it can be an arduous appeal process to get approved. It's pretty easy for a doctor to qualify any low AHI patient under the Excessive Daytime Sleepiness or Insomnia conditions, if they truly want to get a CPAP.
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You are absolutely correct about the importance of selecting the right sleep center and the right doctor. You have the benefit of extensive self-education and prior experience. However, when someone first suspects that there is something wrong with their sleep, how can they begin to know how to select the right sleep center or doctor? They usually don't even know what questions they should ask in order to figure it out.
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You are probably right.
But I would never go to a doctor (or a sleep center) before I have checked them on the internet. Of course it is no guarantee, but in many cases you can get a good insight in the service they provide.
BTW. I always do this, also with other companies, I am dealing with.
Henning
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Well, after not being too impressed w/an "accredited" sleep lab I learned: if it is w/in a reasonable distance at all GO TO THE LAB, ask to see the sleeping rooms, talk to the staff and ask questions: do they take self-referrals or is your own doctor's referral needed? do you have a consult w/the doctor BEFORE your sleep evaluation? do you have a consult w/the doctor AFTER your titration if Dx'd w/OSA and BEFORE your equipment order (script) is written? do you have any input into the equipment that will be ordered? who does the scoring? are all of their sleep techs RPSGTs or are some in training? what is the prime specialty of the sleep doctor who will be interpreting and dicating results of your studies? is this doctor a certified sleep specialist? is the sleep doctor averse to your taking an active part in your therapy, will he/she be willing to work w/you as a TEAM? how long does it usually take to get your test results? are you provided w/a copy of just the doctor's dictation or also w/a copy of the full scored data summary report w/condensed graphs? how soon can you expect to receive them? will the doctor go over and explain those results w/you?
And, of course, you want to call your insurance company to ask what sleep centers they are contracted w/and what local DME suppliers they are contracted with.
National Jewish in Colorado and Stanford in California appear to be two of the top sleep centers in the USA. If you have lung problems in addition to plain ole garden variety sleep disorder(s) I'd tend to pick National Jewish as the leading lung center in the country.
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I had a consultation with my ENT surgeon today. For 2 - 3 month ago I had a nose surgery (deviated septum, sinus surgery and a coblation on my turbinate’s).
Before this surgery I had a lot of problems even with a very low AHI.
Read my discussion:
http://www.sleepguide.com/forum/topics/apnea-pressure-harmful-effects
Today my nose really are function very well (the best for decades). Currently I don't use my CPAP. But if I use it then my AHI is the same as before my nose surgery, but today I really feel good, so I'm sure that the AHI numbers do not tell how you have it. Only you self can do this.
So I'm sure there are a lot of other factors who should be considered, to find out the severity for SA, and the treatment.
I’m sure that I am not “cured” for my SA, but for this moment I feel better without my CPAP than before my surgery – with my CPAP. In fact I feel I'm "normal".
I'm waiting for my next sleep study (a full PSG) and I am curious to the outcome, and then I will take care of my further treatment.
Henning
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Of course AHI has some importance, especially with severe SA as you have.
But I am still of the view that there is too much focus on the numbers of AHI.
After your treatment, your AHI numbers are very fine, but IMO the question is - do you feel well. If so then your treatment is a success. Of course I am aware that it may take some time before the treatment works.
Henning
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We see more and more there seems to be well treated for their SA, seen from the AHI numbers. But they still complain of a wide range of symptoms. I think that there are numerous other factors in sleep disorders that plays a role.
It is the one part, but I also believe that perhaps in many cases it requires a change in lifestyle. Perhaps, for example overweight is not a major factor in SA, but I believe it is a major factor in one's wellbeing. This also applies to persons without SA.
I also believe that exercise is an important factor. So because we are well treated as SA patients, we get it not automatically better than those without SA.
We also need to do something by ourselves, like people without SA, for our wellbeing.
Henning
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Permalink Reply by Steven Y. Park, MD on
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Sorry to jump in so late, but having a newborn baby can really put a damper on my computer discussions time :)
I totally agree with Henning. The AHI is an outdated measure that really hasn't changed significantly in decades. The sleep docs have been debating this problems for years, but so far there's no consensus and the debates go on. Sometimes, there's no correlation between the AHI, oxygen desaturation, or clinical symptoms. I have some patients with an AHI in the 80s who have no symptoms whatsoever, and others with an AHI of 6 who can't function at all.
One area of constant debate is the definition of hypopnea. In this month's issue of SLEEP, an article describes the new American Academy of Sleep Medicine's criteria for scoring hypopneas, and how it compares with two other definitions. We all agree that an apnea is a total cessation of breathing for 10 seconds or longer. The AHI is the (total number of apneas plus the hypopneas) / total number of hours. In brief, there are three ways of defining hypopnea:
1. The "Chicago" criteria (1999): >10 second pauses of >50% decrease in airflow, or those with lesser airflow limitation with oxygen desaturation of 3% or more.
2. The AASM "recommended" criteria (2001): >10 second event with >30% decrease in nasal pressure AND >4% oxygen desaturation. This is what Medicare uses.
3. The "alternative" criteria:>10 second pauses of >50% decrease in nasal pressure AND (>3% desaturation OR arousal).
What the paper showed was that there is a significant difference in the total AHI reported by using theses three definitions of hypopnea. In their sample patients (328 total), here are the AHI calculations using the three different criteria:
Chicago: 25.1
Recommended: 8.3
Alternative: 14.9
What a big difference!
I wish they would get their act together and require only one definition across the board. Since Medicare uses the AHI threshold of 5 for people who are symptomatic or have complications of obstructive sleep apnea, this has huge implications. Better yet, as Henning and all the sleep researchers suggest, come up with a totally different way of quantifying the severity of sleep-breathing problems.
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