A retrospective study of the isoflurane-sparing and cardiovascular effects of combined remifentanil-ketamine infusions with and without lidocaine in cats

OBJECTIVE: This retrospective study aimed to evaluate the intraoperative isoflurane-sparing and cardiovascular effects of a combined infusion of remifentanil-lidocaine-ketamine versus remifentanil-ketamine for balanced anaesthesia in cats to investigate the effect of lidocaine infusion in various clinical situations.

MATERIALS AND METHODS: Among patients with various health statuses undergoing surgical procedures, 18 cats administered remifentanil-lidocaine-ketamine were compared with 20 cats administered remifentanil-ketamine. In the remifentanil-lidocaine-ketamine group, lidocaine was initially infused at 50 μg/kg/minute with a loading dose of 0.6 mg/kg, and the infusion rate was controlled depending on cardiovascular alterations. Linear regression was used to relate end-tidal isoflurane and cardiovascular effects, including blood pressure [expressed as the ratio of mild hypotension duration (mean arterial pressure <60 mmHg) to total anaesthesia time] and heart rate (interquartile range) with patient, surgical and anaesthetic variables including lidocaine infusion.

RESULTS: In the remifentanil-lidocaine-ketamine group, the average lidocaine infusion rate during the entire anaesthetic period was 46.00 ± 12.00 (range: 22.67 to 64.63) μg/kg/minute. The multivariable regression model of end-tidal isoflurane showed a correlation with the duration of the procedure and lidocaine infusion. The end-tidal isoflurane concentration exhibited a significant reduction in the remifentanil-lidocaine-ketamine group (1.16% ± 0.19%), compared with that of the remifentanil-ketamine group (1.27% ± 0.14%). The association between lidocaine administration and hypotension was not significant, nor was that with heart rate.

CLINICAL SIGNIFICANCE: Although the use of intravenous lidocaine in cats has been associated with concerns regarding cardiovascular toxicity, the findings of this study suggest that lidocaine infusion, as part of the remifentanil-lidocaine-ketamine combination, can be considered a component of balanced anaesthesia in cats.