(10-23-2019, 09:08 AM)slowriter Wrote: So are you saying those respiration numbers indicate, on balance, an improvement? 600 median TV should be better than 480 or 500?
I know TV is related to body size/height. I'm a 6' male.
When I started typing this reply I had no idea it would get this long. Well it is here now. I hope you find it of some value. Lol.
At 6' tall a median Minute Volume of 9.13 and median Tidal Volume of 600mL on an ongoing basis are considered undesirably high and puts you at higher risk of Ventilator Induced Lung Injury (VILI).
So what should Minute Ventilation and Tidal Volume be?
Theoretically attaining, monitoring and maintaining of balance of ideal SpO2 and ETCO2 levels would be the method to determine the exact proper Minute Ventilation needs for each person.
In the absence of a means to measure ETCO2 we assume general 'normals' until we learn a reason to deviate.
Normal Tidal Volume for a 6' male:
A generally accepted default goal TV seems to 6mL/Kg * Predicted Body Weight (PBW).
For in hospital ventilation and long term xPAPs the most common current view I see is for a Protective Lung Ventilation strategy using Minute Ventilation of 6mL/Kg per minute for health people, and sometimes 4mL/Kg for restricted lung patients and examples even down to 2mL/Kg + 100% Oxygen for use during surgeries where TV is set very low to keep reduce lung movement.
Below is a handy dandy table to identify your Predicted Body Weight and recommended Tidal Volume at 6mL/Kg. I really like this version of the table because it up top it includes a nicely simple presentation of the ARDSNet Ventilation implementation protocol. Step by step. Those steps do not directly tie to home xPAP use and in no way replace any of the existing titration guides. I like visibility of the ARDSNet protocol as a tool to better understand the overall dynamics of what we are trying to achieve.
At 6' tall your PBW is 78 Kg and your ideal Low Tidal Volume Lung Protective value that provides for a healthy balance of both enough not too much airflow is 466mL
(TV=466mL/breath).
[attachment=16470] ... for some reason the cool handy-dandy Predicted Body Weight & Tidal Volume lookup table attachment appears at the bottom of the message.
Normal Minute Ventilation for a 6' male: MV = Reps Rate * Tidal Volume
Most often I see 6L/min listed at the norm for health patients and the acceptable population range 5-8L/min. The common printed example is (TV=500mL) * (RR=12) = 6L/min.
At the expected norm of 12 breaths per minute this gives you baseline target sleeping Minute Ventilation of 5.6L/min (12 breaths a min * TV of 466ml).
If a Minute Vent of 5.6L/min seems a bit low that is because it is. The HHS/NIH and ARDSNet protocols are published with expected short term, 28 days of use. It is accepted that these recommended TV values are known to not be enough volume to flush out enough CO2 for long term use.
Ok, so what should is my ideal Minute Ventilation Value:
We know some studies report an average healthy ~35 year old male has a Tidal Volume at rest during the day of 7.3L/min and at night 7.15L/min. So if I was 6' tall to create my real MV target I would personally just adopt the 466mL per breath as the Tidal Volume currently recommended as the best number/value to protect and preserve my pulmonary system and mate it to my rough average Respiratory Rate of 15.
This will give me a baseline ideal of Minute Volume of 7 L/min (MV 6.99L/min = (RR 15bpm * TV 466ml)) which quite nicely maps to commonly published normal MV around 7L/min.
So we have our pragmatic working baseline ideals:
- Minute Volume of 7 L/min (6.99L/min) (RR 15bpm * TV 466ml)
- Tidal Volume of 466mL per breath
- Respiratory Rate of 15 breaths per min
At 6' I would use a Minute Volume (MV) of 7 L/min as an anchor value everything adjusts around. When Respiratory Rate increases or decreases I will seek to adjust (as much as I can) my Tidal Volume up or down to always maintain 7 L/ min of MV (MV 7L/min = RR & TV).
WillSleep