Effect of a 7.2% hypertonic saline solution infusion on arterial blood pressure, serum sodium concentration and osmotic pressure in normovolemic heifers.

The effects of an intravenous (i.v.) infusion of a small volume (5 ml/kg) or large volume (15 ml/kg) of hypertonic saline solution (HSS; 7.2%, 2,400 mOsmol/kg.H2O) and those of an i.v. infusion of 5 ml/kg isotonic saline solution (ISS; 300 mOsmol/kg.H2O) on plasma volume, arterial blood pressure, serum sodium concentrations and osmotic pressure were investigated in conscious heifers. Nine heifers (3 heifers/group) were monitored for 120 min after the initiation of fluid replacement. The relative plasma volume (rPV) in the 5 ml/kg HSS and 15 ml/kg HSS progressively increased to 137.7 +/- 2.4% at t = 5 min and 145.2 +/- 5.4% at t = 15 min, respectively. The expanding plasma volume in the 5 ml/kg HSS group remained at an up to 10% higher level until 120 min, but not in the 15 ml/kg HSS group. The 5 ml/kg HSS infusion induced transit high-osmotic (305.3 +/- 4.0 mOsmol/kg.H2O) and sodium levels (155.7 +/- 3.5 mM/l) at t = 5 min. However, the 15 ml/kg HSS infusion induced constant high-osmotic level (321.7-336.7 mOsmol/kg.H2O) and hypernatremia (162.8-170.0 mM/l) from t = 10 min to the rest of the experiment period. In the ISS and 5 ml/kg HSS groups, no changes in PaO2 were observed. The 15 ml/kg HSS infusion induced a significant decrease in the partial pressure of oxygen at the t = 30 min compared to the t = 0 min values. On the basis of these findings, a small volume (5 ml/kg) HSS infusion can be rapidly and safely administered to cattle for expanding the plasma volume without inducing hypernatremia. A 5 ml/kg HSS infusion is thus recommended for the initial field resuscitation of cattle.