Plasma volume expansion with colloids increases blood-tissue albumin transport

Abstract

Extravasation of plasma proteins is increased after volume expansion with whole blood or plasma. To investigate the mechanisms responsible for this phenomenon, we measured extravascular accumulation of exogenous 131I-labeled bovine serum albumin in several tissues and organs of anesthetized rats. Plasma volume was increased acutely by infusion of isoncotic albumin or polyvinylpyrrolidone, with or without subsequent infusion of a 1:10 dilution of the colloid to induce blood-to-tissue fluid movement. Controls were given only a slow sustaining infusion of saline. The amounts of fluid and plasma protein lost from the circulation were followed simultaneously by two methods: 1) material balance in the whole animal, and 2) changes in 131I-labeled albumin uptake (VA) and water content (VW) in the individual tissues. Plasma volume expansion of 80-90% increased plasma protein extravasation in the whole rat by an average of 2.7-fold over a 30-min period. Of the protein extravasated, 42% entered the abdominal cavity. The rest was distributed in the interstitial compartment of various tissues and organs. Tracer albumin accumulation (averaged over 30 min) was increased 38-82% in skin and paw, 40-59% in skeletal muscles, 131% in hearts, and 167-230% in different parts of the intestine. Increased convective transport does not appear to be a major factor. There was little or no relation of albumin transport increase to the magnitude or direction of net fluid transfer. Coupling of albumin transport to volume flow was not greater than previously reported for saline infusion or venous congestion. Convective redistribution (convective transport without net fluid transfer, "volume recirculation") is estimated to increase albumin transport no more than 10% under the conditions of our experiments. The greater part of the increase is thus dissipative, i.e., attributable to increased diffusion or increased vesicular exchange. Control of dissipative transport of albumin may play an important role in regulating plasma volume.

Volume expansion and plasma protein clearance during intravenous infusion of 5% albumin and autologous plasma

“…Renkin et al [1] reported the increased elimination of 125 I-labelled albumin 30 and 60 min after letting iso-oncotic albumin expand the plasma volume by 80-90 % in rats. Albumin uptake was found in the viscera, heart and skin.…”

“…The plasma concentrations of infused proteins increase, whereas the dilution resulting from the plasma volume expansion reduces the concentrations of other proteins. Moreover, the transport of albumin from blood to the interstitial fluid increases [1]. The sum of these alterations may be relevant to postoperative morbidity and to critical illness, which includes organ dysfunction associated with a high transcapillary escape rate for proteins [2,3] and coagulation disorders [4].…”

Starling, plasma protein in tissue fluid, and capillary pulse pressure

“…In the intact animals [7,9,10] circulation was driven by the heart, by a pulsatile (confirmed by Rippe) pump in the isolated limbs, vasodilatated by papaverine [8]. Vasodilatation may have occurred in the plasma volume-expanded rats, e.g., because increased central venous pressure did not raise arterial pressure [9]. Does very high P V enhance [8] or induce [10] vasodilatation metabolically?…”

“…Might the explanation reside in two sets of pores ( Figure 1)? Small pores of the glycocalyx which lines the luminal side of endothelial cells, fenestrae and cell junctions permit filtration of very low-protein fluid, while very sparse large pores offer little resistance to convection of protein [6][7][8][9][10][11]. Increase of COP t seems to oppose absorption at small pore ( Figure 1B) and fenestral exits [11].…”

“…At low venous pressure (P V ), clearance can be calculated to have increased in the order, rat muscle [7,9], dog paw [10], muscle of plasma volume-expanded rats [9], all in intact animals and (increase ,7-fold) isolated rat limbs [8]. Clearance increased gradually at a moderate rise of P V , very strongly at P V ,50 mmHg ( [8,10] incl.…”