Alicia M Skelding, Alexander Valverde
From baseline, all three doses of NE caused significant increases in SAP, MAP, DAP and end-tidal CO2 at 7 and 15 minutes of infusion, and HNE caused a significant increase in CI at 15 minutes (61 ± 13 versus 102 ± 18 mL kg-1 minute-1, respectively; p = 0.002). HR increased significantly at 15 minutes with INE and throughout the infusion with HNE [123 ± 18 at baseline, 149 ± 10 at 7 minutes (p = 0.001) and 155 ± 10 beats minute-1 (p = 0.002)]. INE and HNE were associated with arrhythmias.
OBJECTIVE: To determine the cardiovascular effects of increasing doses of norepinephrine (NE) in healthy, isoflurane-anesthetized cats.
STUDY DESIGN: Prospective experimental study.
ANIMALS: Eight healthy, 1-year-old, neutered male domestic shorthair cats with body masses of 4.7-6.8 kg.
METHODS: Cats were premedicated intramuscularly with butorphanol, midazolam and alfaxalone. Anesthesia was induced with intravenous alfaxalone and maintained with an end-tidal isoflurane concentration of 1.9-2.1% to cause hypotension, under volume-controlled ventilation. NE was administered to cats at three doses in the following order: low, 0.1 μg kg-1 minute-1, intermediate, 0.5 μg kg-1 minute-1 (INE), and high, 1.0 μg kg-1 minute-1 (HNE). Infusions lasted 15 minutes, followed by an interval of 10 minutes, to reach steady state at each phase. Cardiopulmonary variables recorded before (baseline) and during the NE dose included heart rate (HR), cardiac index (CI), and direct systolic, mean and diastolic arterial blood pressures (systolic arterial pressure [SAP], mean arterial pressure [MAP], diastolic arterial pressure [DAP]). Effects within each dose and between doses on cardiovascular variables were compared using one-way and two-way repeated-measures ANOVAs, respectively, followed by multiple pairwise comparisons with a Tukey's test (p < 0.05 was considered significant).
RESULTS: From baseline, all three doses of NE caused significant increases in SAP, MAP, DAP and end-tidal CO2 at 7 and 15 minutes of infusion, and HNE caused a significant increase in CI at 15 minutes (61 ± 13 versus 102 ± 18 mL kg-1 minute-1, respectively; p = 0.002). HR increased significantly at 15 minutes with INE and throughout the infusion with HNE [123 ± 18 at baseline, 149 ± 10 at 7 minutes (p = 0.001) and 155 ± 10 beats minute-1 (p = 0.002)]. INE and HNE were associated with arrhythmias.
CONCLUSIONS AND CLINICAL RELEVANCE: Norepinephrine is effective in a dose-dependent fashion at treating isoflurane-induced hypotension in healthy cats.