Estimating CPAP Pressure Requirement

Brent Hutto · Post by **Brent Hutto** » Fri Mar 03, 2006 1:24 pm

I happened across an interesting formula in a medical journal article [1] I was reading. It gives an estimation equation for the pressure required in CPAP treatment. Here's the formula (units in centimeters):

Pressure = -5.12 + (0.13*BMI) + (0.16*Neck Circumference) + (0.04*AHI)

It might be neat to run this calculation using your own BMI and neck circumference along with the AHI estimated from your baseline sleep study. Then you could compare the predicted pressure with the pressure that you actually used when you started CPAP therapy. Mine works out to between 6cm and 7cm so it will be interesting to see if that's what my titration study came up with. Actually, that would be nice since that's a lower pressure than many people apparently have to sleep with.

[1] Series F. and I. Marc (1997). "Efficacy of Automatic Continuous Positive Airway Pressure Therapy That Uses an Estimated Required Pressure in the Treatment of the Obstructive Sleep Apnea Syndrome". Annals of Internal Medicine.

th · Post by th » Fri Mar 03, 2006 1:58 pm

Brent, I must be doing something wrong....with the formula

any help...data below

BMI is 30.2
neck size is 19
AHI sleep study 59

My titration was 9

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CPAPopedia Keywords Contained In This Post (Click For Definition): Titration, AHI

Brent Hutto · Post by **Brent Hutto** » Fri Mar 03, 2006 2:06 pm

th wrote: BMI is 30.2
neck size is 19
AHI sleep study 59

My titration was 9

You have to express the neck size in centimeters (19"=48cm) which by my ciphering gives you a predicted pressure setting of 8.9cm. Sounds like you're the poster child for that prediction formula.

th · Post by th » Fri Mar 03, 2006 2:10 pm

Brent

Thanks,...........I never did like math

And to think I paid them over $5000.00 When I could have bought a $2 calculator
th

wading thru the muck! · Post by **wading thru the muck!** » Fri Mar 03, 2006 2:18 pm

Works for me too???

This formula results in nearly exactly my titrated pressure... the problem is, my titrated pressure of 7cm is 2cm less than the 9cm I require as proven out by 16 months of APAP data.

Brent Hutto · Post by **Brent Hutto** » Fri Mar 03, 2006 2:26 pm

Well Mucky, for the people in the study I cited the formula tended to either be correct or underestimate them by a couple cm so it sounds like you and TH pretty much bracketed the usual range of results. Look at it this way, with the $5,000 you save on sleep study you can buy a really nice APAP.

Note: Just Kidding! Lest anyone think I posted the formula because I don't think you need an actual diagnosis...no way.[/i]

snorzalot · Post by **snorzalot** » Fri Mar 03, 2006 2:36 pm

This is an interesting formula and is exactly where my PAP setting was configured in 1999 @ 8cm H2O.

Height = 6'7", Weight = 280, BMI = 31.5, Neck = 18 inches or 45.72 cm, AHI=50.5, so

1. Pressure = -5.12 + (0.13*31.5) + (0.16*45.72) + (0.04*50.5)
2. Pressure = -5.12 + (4.095) + (7.3152) + (2.02)
3. Pressure = 8.3102 cm H2O

That's nice, but I still had an AHI of 22 with a pressure setting of 10!
I'm currently on BiPAP with 16 iPAP and 12 ePAP and it's working well

I like this formula though!

Thanks!

snoozalot · Post by **snoozalot** » Fri Mar 03, 2006 2:41 pm

Pretty amazing! I was titrated at 6. The formula says 6.3! I have my apap set for 6-10, and spend about 70% of my time at 6-7, with the balance in the 8-9 range.

Brent Hutto · Post by **Brent Hutto** » Fri Mar 03, 2006 2:50 pm

It is pretty cool. I do this stuff for a living and when something gets published like that it usually works for like 90% of the people in a similar population to the one they used to develop the formula (if it didn't work that well it wouldn't have been published and cited).

Of course anything that's just a regression equation fitted to a whole population is going to have a few people where it doesn't work at all. But on the other hand, there will be a few people who have a full-night titration study and end up with a totally wrong effective pressure measurement. Nothing like this is ever quite so cut-and-dried and "scientific" as it seems.

th · Post by th » Fri Mar 03, 2006 2:58 pm

Brent, Thanks for posting this. This is amazing how many people this works for.......... You know I never did see any sleep equipment at the sleep lab I went to. I bet there was only a tech in the next room with a $2 calculator doing my titration
th

wading thru the muck! · Post by **wading thru the muck!** » Fri Mar 03, 2006 3:04 pm

th wrote:Brent, Thanks for posting this. This is amazing how many people this works for.......... You know I never did see any sleep equipment at the sleep lab I went to. I bet there was only a tech in the next room with a $2 calculator doing my titration
th

th,

This is exactly what I was thinking.

...maybe we need to open the cpaptalk "virtual sleep lab."

Goofproof · Post by **Goofproof** » Fri Mar 03, 2006 10:35 pm

Which shell was the pea under again?

scuba-do · Post by **scuba-do** » Sat Mar 04, 2006 12:55 am

I guess I am an exception to the equation. The equation would estimate my required pressure to be 3.6cm. My titration pressure was 8cm and I am currently using 9cm but think I may need to move up to 10cm.

Darth Vader Look · Post by **Darth Vader Look** » Sun Mar 05, 2006 1:42 am

Math, you gotta love it. Haven't had a chance to check it out yet but I will see if I fit the bill for this.