Transcapillary fluid balance in pre-eclampsia

Summary. The fluid transport between the plasma and interstitial fluid compartment is governed by the Starling forces, i.e. the capillary pressure (P_c), interstitial fluid hydrostatic pressure (P_i) and colloid osmotic pressure in plasma (COP_p) and interstitial fluid (COP_i). Interstitial fluid was collected from subcutaneous tissue on the thorax and ankle by implanted wicks and Pi was measured using the ‘wick-in-needle’ technique. In pre-eclampsia, COP_p, is reduced due to hypoproteinaemia and this predisposes towards loss of fluid from the vascular compartment. An important oedema-preventing mechanism is reduction of COP_i, which serves as a homeostatic buffer against increased capillary filtra-tion. This mechanism works in moderate, but not in severe preeclampsia. A higher COP_i was found both at the thorax (8·3 vs 7·0 mmHg) and ankle (5·9 vs 3·9 mmHg) in the group with severe pre-eclampsia compared with the group moderate pre-eclampsia, in spite of a significant reduction in COP_p (15·5 vs 19·9 mmHg). These findings suggest that an increased microvascular permeability of plasma proteins to subcutaneous tissue contributes to COP_p reduction in severe pre-eclampsia.