Feasibility of an electric current stimulator device to assess the sensory response after transversus abdominis plane block in Guinea pigs (Cavia porcellus)

Abstract

Objective To assess the feasibility of using an adjustable intensity nerve stimulator for evaluating the sensory response after a transversus abdominis plane (TAP) block in guinea pigs (Cavia porcellus)Study design Prospective, randomized, blinded, experimental crossover study. Animals A total of six adult guinea pigs (Cavia porcellus).Methods Trial A involved a unilateral TAP block with 0.5% bupivacaine (1 mL kg–1), while trial B was a unilateral sham block with an equivalent volume of 0.9% saline. In both trials, the noninjected side served as the control. An electrical stimulus was bilaterally applied at 10, 20, 30, 60, 90, and 120 minutes postinjection. Stimulus intensity was gradually increased and the current intensity (mA) at which a response (body movements and/or voluntary limb withdrawal and/or vocalization) occurred on each side was registered. Measurements over time (Friedman test) and between sides at each time point (Wilcoxon test) were compared.Results In trial B, nonsignificant differences were observed between sides at each time point. In trial A, when comparing responses at each time point, nonsignificant differences were observed at 60 (p = 0.104), 90 (p = 0.598), and 120 minutes (p = 0.891); however, at 10 (p = 0.043), 20 (p = 0.027), and 30 minutes (p = 0.026), significant differences were observed. The stimulus intensity necessary to evoke a response in the bupivacaine-injected side was at least 23.8% higher than the current intensity required to elicit a response in the control side.Conclusion and clinical significance The electrical stimulus method appears effective in distinguishing the presence or absence of sensory blockade in guinea pigs that received a TAP block. This approach may also serve to assess the onset time and duration of the block.