The dynamics of vascular volume and fluid shifts of lactated Ringer's solution and hypertonic-saline-dextran solutions infused in normovolemic sheep

Infusions of hyperosmotic-hyperoncotic solutions such as hypertonic saline dextran (HSD) are used in Europe for resuscitation of traumatic shock and p erioperative volume support as an adjunct to conventional isotonic crystall oids. Whereas plasma volume expansion of HSD has been measured at single ti me points after the intravascular volume expansion, the detailed time cours e of fluid shifts during and after infusions have not been reported. We com pared the time course of volume expansion during and after 30-min infusions of 4 mL/kg HSD and 25 mL/kg lactated Ringer's solution (LR) in normovolemi c conscious splenectomized sheep. Peak plasma volume (Evans blue and hemogl obin dilution) expansion was similar for HSD (7.8 +/- 0.9 mL/kg) and the la rger sixfold volume of LR (7.2 +/- 0.5 mL/kg). However, 30 min after the 30 -min infusion (T60), plasma expansion remained larger after HSD (5.1 +/- 0. 9 mL/kg) than after LR (1.7 +/- 0.6 mL/kg). Both solutions caused an equiva lent diuresis. Intravascular volume expansion efficiency (VEE), defined as milliliter plasma expansion/milliliter fluid infused at 0 (T30), 30 (T60), and 60 (T90) min after infusion ended was 1.8, 1.3, and 0.8, respectively f or HSD, whereas LR provided a VEE of only 0.27, 0.07, and 0.07. The relativ e expansion efficiency of HSD versus LR, calculated as the ratio (VEEHSD/VE ELR), was 7-fold that of LR at the end of infusion T30, and 20-fold at T60, but decreased to 9-fold by T120. Intravascular volume dynamic studies of d ifferent volume expanders in animals and patients may provide anesthesiolog ists with a new tool for monitoring the effectiveness of fluid therapy.