The choice of the intravenous fluid influences the tolerance of acute normovolemic anemia in anesthetized domestic pigs

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.

Crystalloids versus colloids during acute normovolemic anemia: the quest continues...

“…During severe hemodilution, exhaustion of subendocardial flow reserves will cause local ischemia and is the main complication of further blood loss. As shown in the study by Pape and colleagues [1], cardiac index did significantly increase in all groups until the Hb crit was reached in the Ringer's solution. Thereafter, only small changes could be found.…”

“…With this technique the authors could show that the choice of fluid replacement impacts the onset and extent of the Hb crit . In conclusion, the authors propose tetrastarch preparations (for example, HES 130/0.4) as the 'most advantageous regarding maintenance of tissue oxygenation during progressive anemia' [1]. However, this present study undoubtedly has some limitations that suggest a more careful approach regarding the interpretation of its results.…”

“…Pape and colleagues discuss the effect of different volume replacements in a previous issue of Critical Care [1]. In light of the numerous risks associated with allogeneic blood transfusions, many e orts have been made towards blood-sparing management of the perioperative phase [2].…”

“…Pape and colleagues add evidence for the ongoing quest for optimal fluid replacement strategies during acute hemorrhage and address the unresolved controversy of crystalloid versus colloid fluid replacement strategies with the help of an established porcine hemorrhage model [1]. In this particular porcine model Pape and colleagues simultaneously withdrew blood and replaced the volume with 'plasma-expansion-rate-adjusted' amounts of Ringer's solution, gelatine, 6% hydroxyethyl starch (HES) 130/0.4 or 6% HES 450/0.7 and assessed the Hb crit by repetitively measuring oxygen uptake (VO 2 ) in conjunction with a computed regression analysis to detect deterioration indicating critical hemoglobin values.…”

The Limit of Anemia Tolerance during Hyperoxic Ventilation with Pure Oxygen in Anesthetized Domestic Pigs

“…While the use of HES in the clinical setting is presently a matter of controversy, mid-molecular HES preparations have at least in the experimental setting proven effective regarding the maintenance of tissue oxygenation in profound anemia and were in this respect superior to gelatin or to crystalloids [23]. The advantages of HES 130/0.4 were explained with a lower degree of extravasation resulting in a more sustained volume effect and reduced tissue edema formation.…”