Acute Normovolemic Hemodilution in the Pig Is Associated with Renal Tissue Edema, Impaired Renal Microvascular Oxygenation, and Functional Loss

Background: The authors investigated the impact of acute normovolemic hemodilution (ANH) on intrarenal oxygenation and its functional short-term consequences in pigs. Methods: Renal microvascular oxygenation (mu Po-2) was measured in cortex, outer and inner medulla via three implanted optical fibers by oxygen-dependent quenching of phosphorescence. Besides systemic hemodynamics, renal function, histopathology, and hypoxia-inducible factor-1 alpha expression were determined. ANH was performed in n = 18 pigs with either colloids (hydroxyethyl starch 6% 130/0.4) or crystalloids (full electrolyte solution), in three steps from a hematocrit of 30% at baseline to a hematocrit of 15% (H3). Results: ANH with crystalloids decreased mu Po-2 in cortex and outer medulla approximately by 65% (P < 0.05) and in inner medulla by 30% (P < 0.05) from baseline to H3. In contrast, mu Po-2 remained unaltered during ANH with colloids. Furthermore, renal function decreased by approximately 45% from baseline to H3 (P < 0.05) only in the crystalloid group. Three times more volume of crystalloids was administered compared with the colloid group. Alterations in systemic and renal regional hemodynamics, oxygen delivery and oxygen consumption during ANH, gave no obvious explanation for the deterioration of mu Po-2 in the crystalloid group. However, ANH with crystalloids was associated with the highest formation of renal tissue edema and the highest expression of hypoxia-inducible factor-1a, which was mainly localized in distal convoluted tubules. Conclusions: ANH to a hematocrit of 15% statistically significantly impaired mu Po-2 and renal function in the crystalloid group. Less tissue edema formation and an unimpaired renal mu Po-2 in the colloid group might account for a preserved renal function.