Abstract
IntroductionThe correction of hypovolemia with acellular fluids results in acute normovolemic anemia. Whether the choice of the infusion fluid has an impact on the maintenance of oxygen (O2) supply during acute normovolemic anemia has not been investigated so far.MethodsThirty-six anesthetized and mechanically ventilated pigs were hemodiluted to their physiological limit of anemia tolerance, reflected by the individual critical hemoglobin concentration (Hbcrit). Hbcrit was defined as the Hb-concentration corresponding with the onset of supply-dependency of total body O2-consumption (VO2). The hemodilution protocol was randomly performed with either tetrastarch (6% HES 130/0.4, TS-group, n = 9), gelatin (3.5% urea-crosslinked polygeline, GEL-group, n = 9), hetastarch (6% HES 450/0.7, HS-group, n = 9) or Ringer's solution (RS-group, n = 9). The primary endpoint was the dimension of Hbcrit, secondary endpoints were parameters of central hemodynamics, O2 transport and tissue oxygenation.ResultsIn each animal, normovolemia was maintained throughout the protocol. Hbcrit was met at 3.7 ± 0.6 g/dl (RS), 3.0 ± 0.6 g/dl (HS P < 0.05 vs. RS), 2.7 ± 0.6 g/dl (GEL, P < 0.05 vs. RS) and 2.1 ± 0.4 g/dl (TS, P < 0.05 vs. GEL, HS and RS). Hemodilution with RS resulted in a significant increase of extravascular lung water index (EVLWI) and a decrease of arterial oxygen partial pressure (paO2), and O2 extraction ratio was increased, when animals of the TS-, GEL- and HS-groups met their individual Hbcrit.ConclusionsThe choice of the intravenous fluid has an impact on the tolerance of acute normovolemic anemia induced by acellular volume replacement. Third-generation tetrastarch preparations (e.g., HES 130/0.4) appear most advantageous regarding maintenance of tissue oxygenation during progressive anemia. The underlying mechanism includes a lower degree of extravasation and favourable effects on microcirculatory function.
Highlights
The correction of hypovolemia with acellular fluids results in acute normovolemic anemia
Primary endpoint: critical Hb concentation (Hbcrit) Depending on the plasma substitute used for hemodilution, critical hemoglobin concentration (Hbcrit) was met at 2.1 ± 0.4 g/dL (TS-group), 2.7 ± 0.6 g/dL (GEL-group), 3.0 ± 0.6 g/dL (HS-group) and 3.7 ± 0.6 g/dL (RS-group)
The induction of critical normovolemic anemia required the exchange of 69 ± 21% of the circulating blood volume (BV) for Ringer’s solution, 71 ± 19% BV for hetastarch, 93 ± 44% BV for gelatin (P < 0.05 vs. HS- and RS-groups) and 107 ± 28% BV for tetrastarch (P < 0.05 vs. HS- and RS-groups)
Summary
The correction of hypovolemia with acellular fluids results in acute normovolemic anemia. Currently available IV fluids differ in their pharmacodynamic and kinetic profile (for example, molecular weight, plasma half-life, volume expansion effect) and in their effects on rheology and microcirculatory function. We hypothesized that these properties might have an influence on the tolerance of acute normovolemic anemia. In this regard, the present study was conceived to compare potential effects of four commonly used IV fluids: low-molecular hydroxyethyl starch (HES) (tetrastarch, 6% HES 130/0.4), high-molecular HES (hetastarch, 6% HES 450/0.7), gelatin (3.5% urea-crosslinked polygeline), and crystalloid volume replacement with Ringer’s solution
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