IV fluids lactated Ringer's or hetastarch for low blood pressure

Abstract

OBJECTIVE: To determine the effect of IV administration of crystalloid (lactated Ringer's solution [LRS]) or colloid (hetastarch) fluid on isoflurane-induced hypotension in dogs. ANIMALS: 6 healthy Beagles. PROCEDURES: On 3 occasions, each dog was anesthetized with propofol and isoflurane and instrumented with a thermodilution catheter (pulmonary artery). Following baseline assessments of hemodynamic variables, end-tidal isoflurane concentration was increased to achieve systolic arterial blood pressure (SABP) of 80 mm Hg. At that time (0 minutes), 1 of 3 IV treatments (no fluid, LRS [80 mL/kg/h], or hetastarch [80 mL/kg/h]) was initiated. Fluid administration continued until SABP was within 10% of baseline or to a maximum volume of 80 mL/kg (LRS) or 40 mL/kg (hetastarch). Hemodynamic variables were measured at intervals (0 through 120 minutes and additionally at 150 and 180 minutes in LRS- or hetastarch-treated dogs). Several clinicopathologic variables including total protein concentration, PCV, colloid osmotic pressure, and viscosity of blood were assessed at baseline and intervals thereafter (0 through 120 minutes). RESULTS: Administration of 80 mL of LRS/kg did not increase SABP in any dog, whereas administration of <or= 40 mL of hetastarch/kg increased SABP in 4 of 6 dogs. Fluid administration increased cardiac index and decreased systemic vascular resistance. Compared with hetastarch treatment, administration of LRS decreased blood viscosity. Treatment with LRS decreased PCV and total protein concentration, whereas treatment with hetastarch increased colloid osmotic pressure. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that IV administration of hetastarch rather than LRS is recommended for the treatment of isoflurane-induced hypotension in dogs.