Intravenous regional anesthesia in isoflurane anesthetized cats: lidocaine plasma concentrations and cardiovascular effects

Objective To determine if intravenous regional anesthesia (IVRA,) can be used in cats without resulting in excessive plasma lidocaine concentrations or adverse cardiovascular effects. Study design Prospective, blinded crossover study. Animals Seven healthy male young adult cats weighing 3.96 +/- 0.63 kg. Methods At 2.3% end-tidal isoflurane concentration, lidocaine (L) 3 mg kg(-1) (1%) or saline (S) was injected in a distal cephalic venous catheter after application of two tourniquets to that forelimb which remained in place for 20 minutes. Heart and respiratory rates, arterial blood pressures and ECG were recorded every 5 minutes during tourniquet application and for 20 minutes following tourniquet removal. Lidocaine plasma concentrations were measured 5 minutes after injection and 0.5,1, 2,4, 8, 20 and 40 minutes after tourniquet removal. End tidal isoflurane concentrations were reduced to 1.52.0% to elicit a response to toe pinch (RTP) in the contralateral leg. The study was repeated similarly in the contralateral leg and RTP was graded for 40 minutes. Response was also tested in the leg previously injected, the differences between the two scores determined and those differences compared between the L and S treatments. The data were analyzed using ANOVA for repeated measures comparing values to baseline. Significance was set at p < 0.005 using the Bonferroni method for multiple comparisons. Results There were no significant differences in physiologic parameters at either isoflurane concentration, Differences in RTP were significantly larger in the lidocaine treatment. The highest mean lidocaine concentrations were measured 0.5 minutes after tourniquet removal after both injections and were 2.79 +/- 1.05 and 3.10 +/- 1.11 mug mL(-1). The highest individual plasma concentration was 6.46 mug mL(-1). Conclusion No adverse hemodynamic effects were evident after IVRA lidocaine in any cat. The lidocaine dose studied inhibited a RTP until 20 minutes after tourniquet removal. Lidocaine concentrations varied and were measurable prior to tourniquet removal. Clinical relevance IVRA may be a suitable technique for cats undergoing surgery of the distal limbs.