Why our first choice in any patient who’s tachypnec is NIV or PPV ?

In normal breathing we produce a minute ventilation of around 6000 ml/ min
For example we have in normal breathing Vt 500 X 12 = 6000
But does it all going to alveoli and reach the blood? No
We have something

Called anatomical dead space which is the conducting airway.
This takes around 150 Vt of total VT inhaled.
So let’s do a fast calculation
(500-150)x 12 = 4200 this is called * Alveolar ventilation*
But what if the patient is tachypnec due to any disease

Let’s imagine that he has a shallow breathing of 40 RR
VT 150 x 40 = 6000 minute ventilation ! > this is what we really think about

But let’s check the alveolar ventilation
(150-150)X 40 = 0

This 0 cause an anaerobic metabolism to all respiratory muscle and heart muscle and that’s why the patient will be in cardiac arrest if we didn’t support him.
Sequence of RF is First hypoxemia then cardiac arrest then hypercapnia

We use NIV or intubation to guarantee delivery of Vt to alveolar ventilation to ensure use of the tissue and cells to the O2

Target your focus on Alveolar ventilation