Intraoperative isoflurane end-tidal concentration during infusion of fentanyl, tramadol, or fentanyl–tramadol combination in cats

The aim of this study was to evaluate the end-tidal concentration of isoflurane required, clinical parameters, intraoperative antinociceptive effect, and postoperative analgesia in cats undergoing ovariohysterectomy, receiving fentanyl, tramadol, or fentanyl/tramadol. Sixty-six cats in three groups, were premedicated with dexmedetomidine and infused with one of the following treatments: fentanyl, tramadol, or fentanyl/tramadol combination. Anesthesia was induced with alfaxolone and maintained with isoflurane, titrated to keep heart rate, respiratory rate and systolic arterial pressure within target values recorded at endotracheal intubation. An intraoperative cumulative scale was performed. Postoperatively, a short form of the Glasgow Composite Measure Pain Scale Feline was used at 2, 12, and 24 h. The groups were similar for age, weight, dose of dexmedetomidine, and alfaxalone administered. A greater reduction in the end-tidal isoflurane fraction was observed with the combined fentanyl/tramadol infusion than with either fentanyl or tramadol alone. No differences in the end-tidal isoflurane fraction were found between fentanyl or tramadol alone. Hemodynamic stability associated with minimal cardiopulmonary changes, low response to noxious intraoperative stimulation, and low postoperative pain scores were also observed with the fentanyl/tramadol combination. The fentanyl/tramadol combination provided a reduction in the end-tidal isoflurane fraction compared with fentanyl or tramadol alone.