Comparison of 2% mepivacaine and a solution of 2% lidocaine/epinephrine administered for median and ulnar nerve blocks in horses with naturally occurring forelimb lameness.

The research study compares the efficiency of 2% mepivacaine and a solution of 2% lidocaine with epinephrine in reducing lameness in horses. The findings suggest that both anesthetics perform comparably in nerve blocks, with 2% lidocaine with epinephrine potentially acting as a suitable substitute when mepivacaine is not available.

Research Methodology

• The research employed an experimental randomized crossover methodology. Six adult horses with naturally occurring forelimb lameness were chosen to participate in the study.
• The lameness of these horses was measured as a vector sum (VS) by using an inertial gait sensor system.
• After a baseline lameness examination, median and ulnar nerve blocks were administered in the horses. The procedure was performed twice, once using a solution of 2% lidocaine with 5 μg/ml epinephrine, and again using an equal volume of 2% mepivacaine.
• The horses’ movements were observed at 5-minute intervals initially, and then at 30-minute intervals for up to 150 minutes.
• After a 24-hour gap, the nerve blocks were repeated using the other anesthesia.
• The data collected was then analyzed using linear models.

Research Findings

• The results indicate that there was no significant difference in the reduction of the VS, i.e., the severity of lameness, after nerve blocks performed with lidocaine/epinephrine or mepivacaine (P = .791).
• The average time it took for the VS to drop below 8.5mm was shorter for lidocaine/epinephrine (5 minutes) as compared to mepivacaine (9.6 minutes). However, these differences are quite small and suggest similar effectiveness of both anesthetics.
• Importantly, the decrease in VS to less than 8.5mm lasted for 150 minutes in both treatment groups indicating an equal duration of effectiveness.
• In one instance, one horse with the highest VS before treatment did not show a reduction to less than 8.5mm with either of the anesthetics. This exceptional case might indicate varying responses to treatments in different individuals.

Conclusions and Implications

• The study concludes that the outcomes of median and ulnar nerve blocks performed using 2% lidocaine with epinephrine or 2% mepivacaine were comparable. In other words, both anesthetics were equally effective in reducing lameness in horses.
• If availability is a concern, 2% lidocaine with epinephrine can be considered as an adequate substitute for mepivacaine for performing proximal nerve blocks in horses.
• However, considering the exceptional case, further research might be required to better understand nuanced individual responses to both anesthetics.