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

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), and trial B involved 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 post-injection. 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.

Conclusions And Clinical Relevance: The electrical stimulus method appears effective in distinguishing the presence or absence of sensory block in guinea pigs that were administered a TAP block. This approach may also serve to assess the onset time and duration of the block.