Intravenous 15% isoflurane lipid nanoemulsion for general anesthesia in dogs

To investigate the efficacy of a new intravenous (IV) nanoemulsified isoflurane formulation for maintenance of general anesthesia in dogs.

Prospective, crossover, experimental study.

Seven healthy, mature, mixed-breed dogs, three male and four female, weighing 11.5 ± 1.5 kg.

Anesthesia was induced with propofol for instrumentation. Measurements were obtained before administration of either inhaled isoflurane (Iso-I) or IV 15% isoflurane-loaded lipid nanoemulsion (Iso-nano). The minimum alveolar concentration (MAC) of isoflurane was determined using the 'up-and-down' technique. A tail clamp was applied every 15 minutes for a total time of 90 minutes and isoflurane administration was adjusted according to the response. Data were recorded at 30, 60 and 90 minutes for end-tidal isoflurane concentration (Fe´Iso), end-tidal carbon dioxide partial pressure (Pe'CO₂), inspired isoflurane concentration (FIIso), arterial hemoglobin oxygen saturation (SaO₂), peripheral hemoglobin oxygen saturation (SpO₂), respiratory rate (f_R), heart rate (HR), arterial blood pH, PaCO₂, PaO₂, base excess (BE), bicarbonate (HCO₃^-), systemic arterial pressure (sAP), and biochemical variables of blood urea nitrogen, alanine aminotransferase, creatine kinase and creatinine.

No significant differences between treatments were detected for HR, f_R, SaO₂ or any biochemical variables (p > 0.05). In the Iso-nano treatment, sAP was significantly decreased throughout the study. Significant decreases in pH, Pe'CO₂, BE and HCO₃^- were measured in the Iso-nano treatment. Isoflurane MAC was significantly lower in the Iso-nano than the Iso-I treatment. The dose of isoflurane (g hour^-1) required to maintain general anesthesia did not differ significantly between treatments.

Administration of 15% isoflurane-loaded lipid nanoemulsion IV was effective in maintaining general anesthesia in dogs but did not reduce the amount of isoflurane necessary to maintain general anesthesia. Significant hypotension and nonrespiratory acidosis occurred with the injectable form.