Role of Capillary Filtration Coefficient in Volume Expansion in Healthy Volunteers

Abstract

Introduction The goal of intravenous fluid therapy is to expand blood volume (BV). However, only a small portion of the infused fluid volume remains in the vascular compartment. It is generally believed that the rapid vascular escape of fluid is a passive response to volume expansion, specifically, increases in capillary and decreases in oncotic pressure. We sought to determine if the capillary filtration coefficient (Kf) might also be a determinant of vascular volume expansion after a fluid bolus. Methods Healthy volunteers were recruited. Kf, was measured using venous congestion plethysomography before, during and after a 25 mL/kg 0.9% NaCl fluid bolus, administered over 20 minutes. BV expansion (ΔBV) was calculated from the initial plasma volume, by indocyanine dye dilution and from serial hemoglobin measurements Results: There was a rapid but transient BV. Less than 20% of infused fluid remained in the vascular compartment within 45 min after start of fluid bolus. Kf increased 2.5 fold during fluid bolus but returned to baseline values within 60 min. Conclusion Our data suggests rapid fluid extravasation with bolus infusion is augmented by increased capillary filtration coefficient. Research supported by Departmental Funding.