How does your CPAP pressure compare to your predictive value?

[IDRIck]

Some studies have used prediction equations to determine pressures for CPAP while others have used them as an aid in manual sleep laboratory titrations. The equations have some utility but they are not as accurate as a lab titration or an auto titration. How does your cpap or apap pressure compare to the your predicted pressure? Use one of the equations shown below. Note the following abbreviations were used in the equations:

ODI = oxygen desaturation index
NC = neck circumference in centimeters
BMI = body mass index
AHI = apnea-hyponea index

[IDRIck]

Using the Series equation, my predicted pressure is 12.8 cm.
Using the Hoffstein equation, my predicted pressure is 12.1 cm.
My sleep doctor recommended a fixed CPAP pressure of 15 cm.
Using my autoset in apap mode (13 to 17 cm range), the median pressure was 14.9 cm and 95% pressure was 16.9 cm.

[SuperSleeper]

Wow, interesting predictors...

ODI = oxygen desaturation index

I can't seem to find this, but how do find out our Oxygen Desaturation Index? We would have to have a pulse oximeter for that, right? How is the Index figured?

[IDRIck]

Researchers use pulse oximeters that record and electronically score the data. I'm not sure if it's possible to determine with patient grade tools... ODI and AHI are moderately to strongly correlated, depending on the study. I see where you're going though, it would fascinating to see our actual ODI scores and compare with how we respond to therapy or how it changes with changing pressures...

[IDRIck]

I did find some detail that may be helpful if you pulse oximetry data:

"A pulse oximeter with a recording device* is attached to the subject’s finger using a flexible probe; typically, the probe can be attached with tape. The instrument detects 10 data points per minute, each point representing the lowest saturation in a six-second interval. A desaturation event is considered when the hemoglobin saturation level (SaO2) falls below 4% from the baseline saturation. Baseline saturation was considered as the mean saturation in the previous minute. Falls in oxygen saturation to >4% in the interval 90–100% of saturation are also considered as desaturations. The signals are digitalized and recorded using the package software, and manually reviewed by two observers. The total number of desaturations is divided by the hours in bed and an oxygen desaturation index per hour (ODI) is obtained for each patient with three cut-off points: >5 (ODI-5), >10 (ODI-10), and >15 (ODI-15). "

As I understand the above, ODI's are the number of desaturation events per hour. The device evaluates the oximetry data in six second intervals. A desaturation event occurs if the oxygen level is more than 4% below baseline in this six second period. As a side note, during my sleep study, my O2 was below 90% for 110 minutes so I would have a high ODI score if it had been calculated... There would have been 1100 consecutive desaturation events in a row (baseline O2 was 94)...

[SuperSleeper]

Thanks IDRIck...

Paging Paula.... Paging Paula... (or anyone else with one of the consumer-level pulse oximeters)...

Does your device allow you measure the Oxygen Desaturation Index as IDRIck describes above?

[jdireton]

Rick,

Thanks for posting this. My numbers
Series - 11.3
Hoffstein - 10.3

Against a sleep study titration of 12 cmH2O. Very close for a predictive equation.

My CMS 50E pulse oximeter should be capable of giving me the ODI number. I haven't used it in a while but I'll run it tonight and see how well that equation works. Another tool we can use! Interesting stuff.

Thanks again.

[PaulaO2]

Um, no clue. Brain not on all cylinders yet.

Here's a screenshot of a random overnight oximeter reading from back in April. This is the "oximetry summary" report (well, a section of the screenshot I took of it).

[Shastzi]

Using a CMS50-F oximeter here. I'll have to look up the numbers later when I can get to the data files.

[IDRIck]

Shastzi, Jdireton, and Paula, are your ODI numbers before using a CPAP machine? The prediction equations need the pre-treatment values. The ODI equation maybe a good "guess" for those without a sleep study but exhibiting strong symptoms of sleep apnea...

Shastzi, Jdireton, and PaulaO2 how frequently do you use your oximeter?