Effect of the addition of epinephrine to a lidocaine solution on the efficacy and duration of palmar digital nerve blocks in horses with naturally occurring forefoot lameness.

The research study investigates whether adding epinephrine to a 1% lidocaine solution would enhance and extend the effect of palmar digital nerve block (PDNB) in horses suffering from natural forefoot lameness. The results show that the addition of epinephrine proves beneficial without causing any adverse impact on the horse’s heart rate.

Objective and Subjects of the Study

• The purpose of the study was to check if augmenting epinephrine to 1% lidocaine solution would enhance the impact and extend the duration of a Palmar Digital Nerve Block(PDNB) in horses suffering from naturally occurring forefoot lameness.
• The following study was conducted on six adult horses exhibiting natural forefoot lameness.

Procedure Carried Out

• The researchers first performed a PDNB on the affected foot of each horse using a 2% lidocaine solution.
• After an interval of three days, the process was repeated using a 1% lidocaine solution or a 1% lidocaine solution combined with epinephrine (dilution, 1:200,000).
• Following another 3-day washout period, the PDNB was once again performed using the treatment opposite to that used for the second PDNB.
• The horses’ gait was analyzed using a computerized lameness analysis system, and their heart rate and extent of skin sensation between the heel bulbs of the blocked foot were evaluated at predetermined times for 2 hours after each PDNB.

Outcomes of the Research

• The research concluded that there was no significant difference between the effect and duration of the PDNB when using 2% and 1% lidocaine treatments.
• Adding epinephrine to the 1% lidocaine solution was found to be beneficial. It enhanced the effectiveness and increased the duration of the PDNB impact.
• The addition of epinephrine showed a positive correlation with skin desensitization and improvement of lameness.
• The heart rate of the horses remained unchanged during the entire observation phase for all three treatments inclusive of the one with epinephrine.
• No adverse effects associated with PDNBs procedure were observed on any horses during the study.

Conclusions and Clinical Relevance

• Epinephrine (dilution, 1:200,000) when added to a 1% lidocaine solution, was seen to improve the efficacy and prolonged the duration of a PDNB in horses with naturally occurring lameness.
• This finding could be clinically useful for evaluating lameness and standing surgery of the forefoot of horses by making the anesthetic effect more effective and longer lasting.