Effect of anesthetic technique on acute formalin-induced pain in mice

Background and Objectives. The aim of this study was to determine if anesthetic technique influences the degree of acute formalin-induced pain in mice. Methods. Mice were randomized to receive either combined spinal/general anesthesia or general anesthesia prior to a subcutaneous injection of formalin in a hindpaw. The mice in the combined spinal/general anesthesia group received halothane anesthesia and subarachnoid lidocaine. The mice in the general anesthesia group received halothane anesthesia only. After the mice recovered from anesthesia, paw-licking behavior was recorded for 1 hour. A statistical comparison was made using analysis of variance and the Kolmogorov-Smirnov test. Results. The mice in the combined spinal/general anesthesia group (n = 20) had a significantly shorter time to first paw lick (mean ± SD) after formalin injection compared to the mice in the general anesthesia group (n = 20) (16.1 ± 4.5 vs. 22.1 ± 6.3 min, P = .002). No difference was observed in the number of paw licks in the mice receiving either combined spinal/general anesthesia or general anesthesia (40 ± 15 vs. 44 ± 18, P = .47). No difference was observed in the duration of paw licking in either group (231 ± 76 vs. 237 ± 124 s, P = .84). Conclusions. The administration of a pre-emptive subarachnoid lidocaine block in the combined spinal/general anesthesia group did not reduce the degree of formalin-induced paw-licking behavior. Combined spinal/general anesthesia did not decrease acute formalin-induced pain in mice.