The effect of an intravenous (IV) infusion of hypertonic saline solution (HSS; 7.2%, 2,400 mOsmol/kg·H 2 O) was evaluated by serum electrolyte concentrations and osmotic pressure in the anesthetized beagles. Sixteen beagles were assigned to 3 experimental groups (2.5, 5 or 15 ml/kg of HSS IV infusion) or a control group (5 ml/kg of isotonic saline solution (ISS) IV infusion) and were monitored for 120 min after the initiation of fluid infusion. The relative plasma volume (rPV) in the 5 ml/kg

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... 15 ml/kg HSS groups progressively expanded to 143.1 ± 7.4% at 3 min and 156.4 ± 5.9% at 5 min after the initiation of the fluid infusion, respectively. Significant increases were not produced by ISS and 2.5 ml/kg HSS infusion. The serum sodium and chloride concentrations in the ISS group were not altered. The 5 ml/kg HSS infusion induced transient high osmotic and sodium levels, and the serum sodium concentration remained under the 160 mM/l after the completion of the HSS infusion. However, the 15 ml/kg HSS infusion induced a constant high osmotic level (340.5-352.8 mOsmol/kg·H 2 O) and hypernatremia (161.4-174.5 mM/l) from 10 to 90 min after the initiation of the fluid infusion. The 15 ml/kg HSS infusion induced significant decreases in the partial pressure of oxygen (PaO 2 ), reaching 63.7 ± 8.0 mmHg at 120 min after the initiation of the fluid infusion compared with an immediately before fluid infusion value. On the basis of these findings, 5 ml/kg HSS infusion can be safely administered to healthy beagles for expanding the plasma volume without inducing hypernatremia. A 5 ml/kg HSS infusion is thus recommended for the initial field resuscitation of dogs.-KEY WORDS: arterial blood pressure, canine (beagle), hypernatremia, hypertonic saline solution, plasma volume.