Hemodynamic effects of epidural ketamine in isoflurane-anesthetized dogs

Objective—The purpose of this study was to determine the hemodynamic effects of epidural ketamine administered during isoflurane anesthesia in dogs. Study Design—Prospective, single‐dose trial. Animals—Six healthy dogs (five males, one female) weighing 25.3 ± 3.88 kg. Methods—Once anesthesia was induced, dogs were maintained at 1.5 times the predetermined, individual minimum alveolar concentration (MAC) of isoflurane. Dogs were instrumented and allowed to stabilize for 30 minutes before baseline measurements were recorded. Injection of 2 mg/kg of ketamine in 1 mL saline/4.5 kg body weight was then performed at the lumbosacral epidural space. Hemodynamic data were recorded at 5, 10, 15, 20, 30, 45, 60, and 75 minutes after epidural ketamine injection. Statistical analysis included an analysis of variance (ANOVA) for repeated measures over time. All data were compared with baseline values. A P < .05 was considered significant. Results—Baseline values ±standard error of the mean (X ± SEM) for heart rate, mean arterial pressure, mean pulmonary artery pressure, central venous pressure, pulmonary capillary wedge pressure, cardiac index, stroke index, systemic vascular resistance, pulmonary vascular resistance, and rate‐pressure product were 108 ± 6 beats/min, 85 ± 10 mm Hg, 10 ± 2 mm Hg, 3 ± 1 mm Hg, 5 ± 2 mm Hg, 2.3 ± 0.3 L/min/m2, 21.4 ± 1.9 mL/beat/m2, 3386 ± 350 dynes/sec/cm5, 240 ± 37 dynes/sec/cm5, and 12376 ± 1988 beats/min±mm Hg. No significant differences were detected from baseline values at any time after ketamine injection. Conclusions—The epidural injection of 2 mg/kg of ketamine is associated with minimal hemodynamic effects during isoflurane anesthesia. Clinical Relevance—These results suggest that if epidural ketamine is used for analgesia in dogs, it will induce minimal changes in cardiovascular function.