By Satvinder

Sharing my understanding on some important aspects we learnt in this journey of understanding machine breathing.

1. Tidal volume should be 6-8 times of body weight in kg. E.g. 50 kg should be between 300-480. Start with lower side of range, so you can move forward to higher range when needed( with months/years time, alveoli regions available for gas exchange will get reduced). We started with 280 in 2010 and it was set around 400 in 2018.
2. Expiratory pressure or peep can be set to 6 comfortably.
3. Setting the breadth per min (BPM)could be tricky as there are many parameters which must be changed when you change this. Generally I feel 13-16 should be ideal. However, if your loved ones is comfortable with good oxygenation at lower or higher value- let that remains.
We started with 12, but during the time of machine received after servicing, this required change. This was around 16 in 2018.
4. Oxygenation in the body depends on volume of air exchange per min. E.g if you set BPM at 12 and tidal volume 300-300*12 equal to 3600 minute ventilation. While setting the same to 15 would lead to 4500 , a jump of 25% and you will see body oxygenation will automatically increase.(however, it should be rightly set according to total minute ventilation one should target according to weight and size of patient).
5. BPM of 15 means each breath made of 4 seconds. So we also need to see how we divide this to correct ratio of inspiratory and expiratory time. When you change anything, try to adjust inspiratory time to value which do not disturb this ratio. Sometimes tweaking here has a huge impact.
6. Now coming to using which machine – bipap, trilogy or any other machine. What we learnt is that *pressure* mode ventilation works best for ALS patients. So the target is to to achieve minimum minute ventilation atleast, so the mode should be set which has range of inspiratory pressure defined. E.g. *bipap avaps* . And good part is machines now have avaps rates (1-5) which is the rate by which machine try to increase or decrease the pressure, if set tidal volume is not achieved and that transition is smooth compared to volume modes
7. You need to keep monitoring for few minutes each breadth and it’s associated parameters displayed on screen to get idea if machine is actually doing what it designed for. I have seen two A40 machines, where this min pressure wasn’t increasing despite higher inspiratory pressure point was set, when tidal volume wasn’t achieved and machine kept on alarming LMV(low mins ventilation).
8. Our mother was too much against ABG test due to pain associated. So we hardly got that done.(only 4-5 times in first year). Main rule of thumb is – if patient is physiologically looking good + basic parameters fine in pulsoxymeter + ventilation in machine is looking good. No need for any investigations or ABG at all.

If you are in doubt about the BIBAP AVAPS setting the general guid line is to use these numbers for the following parameters:

Tidal Volume – 350 to 420
IPAP – 12 to 16
EPAP – 6
Breadth Per Min BPM – 15 to 16

The actual setting for the patient can be attained only after looking at the patients comfort level, speaking to doctors and some trial and error.