Effect of esmolol on fluid therapy in normovolemia and hypovolemia

β-Adrenergic agonists can enhance vascular volume expansion after a fluid bolus. The present study addresses how the β-adrenergic antagonist esmolol influences volume expansion and fluid balance during normovolemia (series 1) and hypovolemia (series 2). Sheep were instrumented, and the spleen was removed. For series 1, continuous infusion of 50 to 100 μg·kg ^-1·min ^-1 esmolol (n = 6) or control (no drug; n = 6) was begun 30 min before administration of a 24-mL kg ^-1 20-min bolus of 0.9% NaCl. For series 2, anesthetized sheep were infused with 50 to 100 μg·kg ^-1·min ^-1 esmolol (n = 6) or control (no drug; n = 6) 30 min before a·20 mL kg ^-1 hemorrhage. Fluid resuscitation (0.9% NaCl) was begun 30 min after hemorrhage. The 24·mL kg ^-1 20-min bolus was followed by titrated fluid therapy. Hemoglobin, fluid in, and urinary output were used to calculate changes in plasma volume (δPV), extravascular volume (δEVV = fluid in j urinary output - ΔPV), volume expansion efficiency (VEE = fluid in/ΔPV), and fluid distribution ratio (ΔPV/ΔEVV). Hemodynamics for both series were similar with the exception of heart rate. In series 1, peak ΔPV was 9.1 ± 1.0 mL kg ^-1 in control and 3.7 ± 1.0 mL kg ^-1 at study end. Esmolol resulted in a lower peak ΔPV (6.4 ± 2.0 mL kg ^-1) and a negative ΔPV (j0.4 ± 0.6 mL kg ^-1) at study's end. Urinary output was lower, and EVV was greater with esmolol. In series 2, esmolol increased fluid requirements (67 ± 7 mL kg ^-1) compared with control (54 ± 5 mL kg ^-1). Esmolol reduced ΔPV/ΔEVV. These data suggest that esmolol impairs the vascular retention of fluid and may increase the amount of volume support during fluid resuscitation.