A Comparison of Dobutamine, Norepinephrine, Vasopressin, and Hetastarch for the Treatment of Isoflurane-Induced Hypotension in Healthy, Normovolemic Dogs

SIMPLE SUMMARY: In anesthetized dogs, hypotension, defined as a mean arterial pressure (MAP) of <60–70 mmHg, has an incidence of up to 60%. It is therefore imperative to avoid the occurrence of hypotension and undertake immediate strategies to treat it. Treatment protocols for the correction of isoflurane-mediated hypotension include lowering or terminating isoflurane administration; lowering isoflurane requirement by using anesthetic adjuncts and analgesics; intravenous crystalloid and/or colloid bolus; and delivering anticholinergics, positive inotropes, and vasopressor drugs. The present study evaluated and compared the hemodynamic effects of dobutamine (DOB), norepinephrine (NEP), vasopressin (VAS), and hetastarch (HES) for the treatment of isoflurane-induced hypotension and established the most effective dosage regimen for the correction of hypotension. In healthy, anesthetized Beagle dogs undergoing acute, severe isoflurane-induced hypotension, NEP administered as an infusion was the most efficient therapy for correcting MAP. However, the DOB, VAS, and HES treatments were unsuccessful in stabilizing the MAP to >65 mmHg, even at maximum doses. ABSTRACT: Isoflurane is a commonly used inhalation anesthetic in species undergoing veterinary care that induces hypotension, impacting organ perfusion, making it imperative to minimize its occurrence or identify effective strategies for treating it. This study evaluated and compared the hemodynamic effects of DOB, NEP, VAS, and HES in twelve isoflurane-anesthetized Beagle dogs. The order of the first three treatments was randomized. HES was administered last. Data were collected before treatments (baseline) and after 10 min of a sustained MAP of <45 mmHg induced by a high end-tidal isoflurane concentration (T0). Once treatment was initiated and the target MAP was achieved (65 to 80 mmHg) or the maximum dose reached, data were collected after 15 min of stabilization (T1) and 15 min after (T2). A 15 min washout period with a MAP of ≥65 mmHg was allowed between treatments. The intravenous dosage regimens started and were increased by 50% every five minutes until the target MAP or maximum dose was reached. The dosages were as follows: DOB, 5–15 μg/kg/min; NEP, 0.1–2 μg/kg/min; VAS, 0.5–5 mU/kg/min; and HET, 6% 1–20 mL/kg/min. DOB improved CO, DO(2), and VO(2), but reduced SVR. VAS elevated SVR, but decreased CO, DO(2), and VO(2). HES minimally changed BP and mildly augmented CO, DO(2), and VO(2). These treatments failed to reach the target MAP. NEP increased the arterial BP, CO, MPAP, and PAWP, but reduced HR. Norepinephrine infusion at 0.44 ± 0.19 μg/kg/min was the most efficient therapy for correcting isoflurane-induced hypotension.