Pulmonary Vascular Permeability Index (PVPI)
When pulmonary oedema is present (measured using Extravascular Lung Water), the next important question is: What is the reason for the pulmonary oedema?
In general there are two main sources of pulmonary oedema:
- Cardiogenic pulmonary oedema
Caused by intravascular fluid overload, hydrostatic pressures increase. The causes fluids to leak into the extravascular space.
- Permeability pulmonary oedema
Vascular permeability is increased by an inflammatory reaction caused, for example, by sepsis. This leads to the increased transfer of fluids, electrolytes and proteins from the intravascular to the extravascular space, along with a normal to low intravascular fluid status and hydrostatic pressure.
A differential diagnosis of the pulmonary oedema is important because the therapeutic approach is quite different. In cardiogenic pulmonary oedema, a negative fluid balance is sought, while in cases of permeability pulmonary oedema treating the cause of inflammation has priority. The Pulmonary Vascular Permeability Index (PVPI) enables this differential diagnosis. This parameter is calculated from the relation between Extravascular Lung Water (EVLW) and Pulmonary Blood Volume (PBV). A PVPI value in the range of 1 to 3 points to a cardiogenic pulmonary oedema, while a PVPI value greater than 3 suggests a permeability pulmonary oedema.
Fig. Cardiogenic vs. permeability pulmonary oedema