V/Q in self ventilating and ventilated pts

Question 1

What do V and Q stand for?

Answer 1

V = ventilation - volume of air entering the alveoli
Q = perfusion - volume of blood flowing through the lungs

Question 2

In a self-ventilating pt where is ventilation and perfusion most optimal and why?

Answer 2

Ventilation and perfusion are both optimal in the lower 1/3 of the lung; AKA dependant lung region.
ventilation - the dependant lung regions sre partially expanded but still has capacity for further expansion and volume change
perfusion - the dependant lung regions are more influenced by gravity, so blood is drawn down to the base

Question 3

In a ventilated pt where is ventilation and perfusion optimal and why?

Answer 3

Ventilation distribution is different due to the positive pressure breath delivered by the ventilator. Air will take the path of least resisitance. Therefore ventilation is optimal in the upper 1/3 of the lung ; AKA non-dependant lung region
Perfusion remains the same - optimal in the lower 1/3 of the lung; AKA dependant lung regions.
There is ALWAYS a V/Q mismatch in ventilated pts.

Question 4

How do you position self-ventilating pts and why?

Answer 4

‘bad lung up’
Encourages postural drainage of the secreted lung with gravity assist
Creates a V/Q match which maximises gaseous exchange

Question 5

How do you position ventilated pts and why?

Answer 5

‘good lung up’
This will cause postural drainage but creates a V/Q mismatch that favours ventilation.

‘bad lung up’ - benefits postural drainage but V/Q mismatch has poor ventilation. Not helpful for ventilated pts.