Pulmonary vascular filtration of starch-based macromolecules: effects on lung fluid balance

Pulmonary edema is a complication of critical care fluid management that may be restricted by the use of oncotically effective resuscitation fluids. Potentially beneficial oncotic properties of starch-based plasma volume expanders such as hetastarch (Het), pentafraction (Pen), and Dextran-70 (Dex) may be compromised by their broad range of molecular masses, some of which are small enough to filter from the circulation. Leakage of these molecules into the pulmonary interstitium may limit their oncotic effectiveness and enhance fluid filtration. We measured the filtration of these three resuscitation solutions into lung lymph to evaluate their oncotic contribution to pulmonary edema formation.

Unanesthetized euvolemic adult sheep, prepared with chronic lung lymph fistulae, underwent plasma volume expansion with Het (n = 6), Pen (n = 6), or Dex (n = 6 ) (6%, 35 ml/kg/90 min). Oncotic effectiveness was determined by measuring plasma and lymph oncotic pressures and the oncotic pressures contributed by each starch. Pulmonary hydrostatic pressures and lung lymph flows (Q(L)) were also measured. Results are expressed as means +/- SEM. Comparisons were made by two-factor analysis of variance.

Dex contributed 9.0 +/- 0.9 mmHg to the plasma oncotic pressure, significantly more than Het and Pen (5.3 +/- 0.6, 6.5 +/- 0.6 mmHg, respectively). However, Dex filtration also contributed 6.1 +/- 0.5 mmHg to the lymph oncotic pressure, compared to 3.1 +/- 0.3 and 4.7 +/- 0.5 mmHg for Het and Pen, respectively (P < or = 0.05). Dex, Het, and Pen raised Q(L) over baseline by 7.7 +/- 1.5, 4.3 +/- 1.0, and 3.2 +/- 0.7 ml/30 min, respectively (P < or = 0.05). Dex increased Q(L) significantly more than Het or Pen.

Pen and Het demonstrated greater oncotic effectiveness because of restricted plasma-to-lymph macromolecular filtration and limited transvascular fluid flux. By comparison, Dex filtered rapidly and increased transvascular fluid filtration. Pen appears to possess filtration properties that optimize critical care fluid management compared to currently available colloid solutions such as Het and Dex.