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    108 Vascular Permeability Index
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    108 Vascular Permeability Index

    Vascular permeability index: Starling forces, glycocalyx, pulmonary permeability index and causes of oedema.

    The vascular permeability index describes how easily fluid and proteins leak from the blood through the walls of the small exchange vessels (capillaries and venules) into the tissues. Fluid movement across the capillary wall is governed by the Starling principle: hydrostatic pressure pushes fluid out, and the oncotic (colloid osmotic) pressure of plasma proteins holds it in. The revised model emphasises the endothelial glycocalyx, a gel-like layer on the inner surface of vessels that forms the main barrier. When permeability increases, oedema forms; in the lungs this causes pulmonary oedema.

    MicrocirculationOedemaPulmonary oedema
    Governed byStarling forces, glycocalyx
    Clinical index (lungs)PVPI by transpulmonary thermodilution
    PVPI ≤ 3suggests hydrostatic oedema
    PVPI > 3suggests permeability oedema (ARDS)
    Pulmonary vascular permeability index by transpulmonary thermodilution: 3 or below consistent with normal permeability or hydrostatic oedema, above 3 consistent with increased permeability as in acute lung injury Pulmonary vascular permeability index (PVPI) Normal / hydrostatic ≤ 3 3 Increased permeability above 3: ALI/ARDS
    Figure 1. Pulmonary vascular permeability index (PVPI). In one study, PVPI of 3 or more identified ALI/ARDS with high specificity; the cut-off varies between studies.

    Causes of increased permeability

    • Inflammation: sepsis, pneumonia, acute respiratory distress syndrome (ARDS), pancreatitis, burns, major trauma, anaphylaxis
    • Damage to the glycocalyx: sepsis, ischaemia–reperfusion, hyperglycaemia, rapid fluid overload
    • Hypoxia and toxins, some medicines (for example in capillary leak syndromes)

    Oedema can also form without increased permeability when hydrostatic pressure rises (hypertension in the pulmonary circulation, heart failure, fluid overload: "cardiac asthma") or when oncotic pressure falls (low albumin in liver disease, nephrotic syndrome, malnutrition). Distinguishing these mechanisms guides treatment: diuretics and heart support for hydrostatic oedema, treatment of the cause and lung-protective ventilation for permeability oedema.

    Seek emergency care

    for sudden severe breathlessness, especially when lying flat, frothy or pink sputum, rapidly spreading swelling, or swelling of the face and throat.

    References

    1. Woodcock TE, Woodcock TM. Revised Starling equation and the glycocalyx model of transvascular fluid exchange: an improved paradigm for prescribing intravenous fluid therapy. Br J Anaesth. 2012;108(3):384–394.
    2. Monnet X, Anguel N, Osman D, Hamzaoui O, Richard C, Teboul JL. Assessing pulmonary permeability by transpulmonary thermodilution allows differentiation of hydrostatic pulmonary edema from ALI/ARDS. Intensive Care Med. 2007;33(3):448–453. doi:10.1007/s00134-006-0498-6

    This article is for general information and does not replace a consultation with a doctor. Measurements must be interpreted by a physician together with symptoms and other tests.

    Published on 7 May 2024