Respiratory - West Zones and pulmonary perfusion Flashcards
What was J.B. Wests big discovery
The gravitational model was established stating that, due to gravity, in the upright patient, the ventilation and perfusion increased from the top to the bottom of the lung.
J.B West recognized that, in addition to the effects of gravity, capillary blood flow to the alveolus is dependent on the pressure of the gas within the alveolus.
Very NB in anaesthesia as PPV significantly alters alveolar pressure
What are the west zones and how are they numbered
West Zone 1 –> top of lung
West zone 2 –> middle
West zone 3 –> base
The arterial, venous and alveolar pressure differ in each zone and hence have implications for the V:Q ratio
How do changes in arterial, venous and alveolar pressure vary relative to each other in each of the west zones 1 - 3. How is the V:Q ration in each zone affected
West Zone 1: PA > Pa > Pv: Very high V:Q (no perfusion)
West Zone 2: Pa > PA > Pv: High V:G (flow only in systole)
West Zone 3:Pa > Pv > PA: Lower V:Q (flow in diastole and systole)
Which of the zones does not exist in normal lungs
West Zone 1
When does West Zone 1 become clinically significant
what happens when West zone 1 does occur
- Very low pulmonary artery pressure (Pa) e.g. shock
- Very high PA –> e.g. high intrinsic PEEP in severe asthma
The result is increase in alveolar dead space and ventilation is wasted
What West zone should the tip of a pulmonary aretery catheter be inflated and why
How can this be tested during placement of the PCWP tip
In West Zone 3.
In order for the measured PCWP to accurately estimate the pulmonary venous pressure (and hence left atrial pressure) there needs to be communication with an uninterrupted static column of blood between the pulmonary artery and the left atrium.
Increase PEEP by 10 cmH2O –> if the PCWP increases by more than 25% it is likely that the tip is not in West Zone 3
