Saline compared to plasma volume replacement after volume depletion in sheep: Lung fluid balance

Abstract

We bled anesthetized sheep until they were severely hypotensive, and immediately infused enough normal saline or autologous plasma to restore systemic blood pressure in order to define differences between the effects of crystalloid and colloid infusions on lung fluid balance. Forces favoring fluid filtration in the pulmonary microcirculation were highest just after the infusion period. Lung lymph flow tripled after saline but increased only 50% after plasma infusion. Lymph flow rate correlated well with the sum of Starling forces throughout the study whether saline or plasma was infused, and the relationship was similar to that when lung vascular pressures were mechanically elevated. Saline-resuscitated animals were the only ones to develop significant increases in postmortem wet-to-dry lung weight ratios (controls = 4.36 ± 0.05; saline = 4.86 ± 0.17, P < .05; plasma = 4.34 ± 0.19, P = NS). After volume depletion, saline eliminated the lymph-to-plasma oncotic pressure gradient while plasma helped to preserve it. Regardless of the type of fluid used to restore circulating volume, hydrostatic pressure was the major determinant of transvascular fluid filtration in the lungs. Lung lymph flow correlated more closely with forces affecting fluid filtration than with lung water content.