Duration of action of mepivacaine and lidocaine in equine palmar digital perineural blocks in an experimental lameness model

Mona Hoerdemann

Knowledge of the duration of action of common local anesthetic agents is required for decision making in equine lameness investigation. The objective of this study was to compare the performance of two local anesthetic agents in a palmar digital nerve block (PDNB). The investigation was performed in two phases. The first phase aimed to assess the reliability of the experimental lameness model to induce and maintain a consistent lameness. The aim of the second phase was to establish the efficacy, onset and duration of action of mepivacaine and lidocaine based on objective, quantifiable lameness and skin sensitivity, and to compare the response across those outcomes. An interventional crossover, cohort study with balanced randomization was used. In the first phase, reversible forelimb lameness was induced in 6 horses, and lameness was quantified and assessed for consistency with an inertial sensor system for up to 180 minutes. In the second phase, reversible forelimb lameness was induced in 8 horses and a palmar digital nerve block (PDNB) was applied with lidocaine or mepivacaine. Quantitative lameness and skin sensitivity data were collected with an inertial sensor system and a force gauge. The times to lameness resolution/skin desensitization (T1), consistent lameness detection/partial return of skin sensitivity (T2) and complete return of lameness/skin sensitivity (T3) were established and compared between treatments and assessment methods. Mepivacaine resolved the lameness in 8/8 horses, lidocaine in 3/8 horses. The remaining 5/8 horses for lidocaine showed persistent lameness. Both treatments achieved complete skin desensitization in 8/8 horses within a mean of 11 minutes and 10 minutes for mepivacaine and lidocaine, respectively. Detection of consistent lameness after PDNB was significantly later for mepivacaine than lidocaine (T2_lameness mepivacaine 169 minutes, lidocaine 36 minutes). Mepivacaine had a significantly longer duration of action for complete return of lameness and skin sensitivity (mean T3_lameness mepivacaine 366 minutes, lidocaine 113 minutes (P=.038); T3_skin mepivacaine 195 minutes, lidocaine 63 minutes [P=<.001]). Skin sensitivity returned significantly sooner than lameness for lidocaine at T3 (P=.015).

Duration of action of mepivacaine and lidocaine in equine palmar digital perineural blocks in an experimental lameness model

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