"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: 3527
Replies to This Discussion
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Permalink Reply by Mike on
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I've given this some thought myself, wondering whether level of oxygen desaturation should really be the metric of focus. after all, we are concerned about AHI primarily because of it's effect on oxygen in the blood, no?
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Permalink Reply by Henning on
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That's my point.
There is no clear correlation between AHI and the oxygen desaturations. There is neither any correlation between CPAP pressure and AHI.
Henning
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Permalink Reply by Bonnie Neathamer on
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It would be nice if you would post a listing of definitions of words and abreviations used in this type of discussion so I would know what the heck you're talking about! I have SA but I'm not a medical person.
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Permalink Reply by sleepycarol on
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This has been posted prior to this discussion. If you search the forum you will find it.
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Thank you Carol,
I was looking after this definitions list. (I knew I had read it). I'm nor a medical person, but have read a lot about SA.
Henning
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I'm not well-versed on this, but there is a newer push afoot in the sleep medicine profession to utilize the RDI (respiratory disturbance index) instead of the AHI (apnea and hypopnea index) which would include those respiratory events that don't meet the AHI criteria. I believe that this would help to determine UARS (upper airway resistance syndrome ?? I did say I wasn't well-versed in this!) .
And we must all keep in mind that OSA and the newer recognized UARS are NOT the only sleep disturbances that can be detected by a full PSG (polysomnography) and, at least for now, most of these other sleep disturbances can't be detected by at-home testing.
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Permalink Reply by Edward Grandi on
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Some years back eminent researchers in sleep apnea debated the issue. Here is link to a summary -
http://www.pulmonaryreviews.com/sep02/pr_sep02_AHIndex.html
Edward Grandi
ASAA
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Permalink Reply by Rock Conner RRT on
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As always, Ed, a helpful contribution to the discussion.
Edward Grandi said:Some years back eminent researchers in sleep apnea debated the issue. Here is link to a summary -
http://www.pulmonaryreviews.com/sep02/pr_sep02_AHIndex.html
Edward Grandi
ASAA
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Hi Judy,
I think in a lot of studies then AHI and RDI is the same. I have found this about AHI vs. RDI:
“The AHI (apnea/hypopneas index) is the average number of apneas and hypopneas per hour of sleep. The RDI (respiratory disturbance index) includes apneas and hypopneas, and may also include other respiratory disturbances such as snoring arousals, hypoventilation episodes, desaturations events, etc. They are often identical, but depending upon what is scored, the RDI may be larger than the AHI.”
It seems to me, that you can use more sensors, and then the RDI score may be larger than the AHI. Whether this includes the PES measurement (Pressure in the esophageal), I don’t know. As far as I know then the PES measurement is the only way to measure for UARS.
But perhaps some of the professionals here can provide a detailed explanation.
I disagree with you about the “at-home testing”.
Take a look at this link:
http://www.embla.com/products/diagnostic/embla/pdf/EmblaBrochure.pdf
This system has been developed for in-lab studies and for at-home studies as well (full PSG). It is a 60 channel system including 32 channels dedicated ECG. I'm sure that many (in-lab) sleep centers don't have such advanced equipment.
At this link you can see some of the sensors:
http://www.embla.com/Products/StudyAccess/
Henning
Judy said:I'm not well-versed on this, but there is a newer push afoot in the sleep medicine profession to utilize the RDI (respiratory disturbance index) instead of the AHI (apnea and hypopnea index) which would include those respiratory events that don't meet the AHI criteria. I believe that this would help to determine UARS (upper airway resistance syndrome ?? I did say I wasn't well-versed in this!) .
And we must all keep in mind that OSA and the newer recognized UARS are NOT the only sleep disturbances that can be detected by a full PSG (polysomnography) and, at least for now, most of these other sleep disturbances can't be detected by at-home testing.
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Thank you yet again, for the information you've been supplying, Henning!!! I, for one, greatly appreciate it!
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It is an interesting article, but also somewhat surprising.
This phrase is actually the most positive regarding AHI I found in the article.
"Because the AHI is imperfect, Dr. Rapoport views it as a marker for the apnea-hypopnea syndrome and not as a definitive metric. He has found the AHI most useful for detecting severe apnea-hypopnea syndrome."
What also was new for me was the following sentence:
"The lack of a standard definition for hypopnea is another limitation of the AHI. Furthermore, measuring hypopnea is difficult because of the inaccuracy of the devices currently available to monitor patients’ airflow during sleep."
I made a little search and I found four different definitions of hypopneas.
That means that there may be differences in AHI between sleep centers, if they use different definitions for hypopneas and/or different equipment.
I think this is a good reason to require a fully data capable CPAP. I am suddenly very happy for my Auto CPAP.
The article is from 2002. I hope that something has changed since. It seems to me that the article is written before the AHI scale of severity was made.
Henning
Edward Grandi said:Some years back eminent researchers in sleep apnea debated the issue. Here is link to a summary -
http://www.pulmonaryreviews.com/sep02/pr_sep02_AHIndex.html
Edward Grandi
ASAA
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Permalink Reply by Daniel on
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I'm a little late to this discussion, but I'd like to contribute a few points:
- UARS can only be detected using PES. Not all sleep labs have PES equipment, and of those that do, some patients decline to have it measured, because the probe stuck up your nose and down your throat can be uncomfortable.
- RDI does not include PES stats. RDI in general has been rejected by the insurance industry, which tends to solely look at AHI. Another statistic, RERA (Respiratory Event Related Arousals) does take the PES measurement into account. With UARS, people can overcome obstructions of the upper airway and get the oxygen levels they need, so there are no apneas and hypopneas. However, the effort to clear the obstruction is so great that it can lead to arousals, sleep fragmentation, and excessive daytime sleepiness.
- It's my understanding the AHI scale was defined at Stanford, and they are the first to acknowledge that the scale does not adequately address the severity of the symptoms of sleep apnea.
- When I work with patients, I always give them a device that records AHI and teach them how to use it and what it means. However, I also remind them that ultimately, it isn't about the numbers. It's about how you feel when you wake up in the morning. ResMed devices have an optional feature called Auto-Appear, which displays the results from the previous night when you turn the device off in the morning. SomniHealth's policy is to leave this feature OFF, because I don't want patients to obsess about their AHI.
- Unless you add some very expensive extras to your CPAP, it does not measure oxygen levels in your bloodstream. Therefore, the "Hypopneas" as measured by a data-collecting CPAP use a definition of hypopnea that has little to do with the variable measures used in sleep labs. Each brand uses a different definition of hypopnea. I have a patient who has both a BiPAP Auto and a VPAP Auto. He uses them with fixed pressures, but the HI on the ResMed device is much higher. At best, the hypopneas readings from your CPAP are only a rough estimate.
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