Duration and Efficacy of Different Local Anesthetics on the Palmar Digital Nerve Block in Horses

The aim of the present study was to determine the duration and efficacy of three local anesthetics in the palmar digital (PD) nerve block. Nine adult horses were randomly allocated in a crossover design (bupivacaine, 5 mg/mL; lidocaine, 20 mg/mL; and ropivacaine, 7.5 mg/mL). The objective lameness evaluations were recorded before and at 5, 10, 15, 30, 60, 90, 120, 150, 180, 210, 240, and 300 minutes after PD block. The relative lameness severity (RLS) was determined and analyzed using the Tukey-Kramer test (P < .05). Lameness improvement (LI) after blocking was determined as a percentage decrease in the quadratic mean (vector sum). The RLS after lameness induction was 4.06 times the threshold (8.5 mm), and the intensity of lameness (time 0) was similar between horses (coefficient of variance = 25%). Five minutes after PD block, all drugs had improved lameness in more than 2.5 times (LI >60%). Bupivacaine, lidocaine, and ropivacaine were effective in blocking at least three times (LI >75%) the experimental lameness. Using 7.5-mg bupivacaine, LI was >3.5 times between 5 and 90 minutes after PD block (LI >83%). With lidocaine (30 mg), between 5 and 90 minutes after blocking a significant LI was observed with a reduction in the lameness intensity greater than 1.2 times (LI >43%). Ropivacaine (11.25 mg) improved lameness in >2.6 times (LI >66%) between 5 and 180 minutes after block. Bupivacaine and ropivacaine showed greater anesthetic effectiveness when compared with lidocaine. The local anesthetics produced a significant LI 5 minutes after blocking. Objective analysis showed a longer analgesic effect of the PD nerve block using ropivacaine than bupivacaine and lidocaine, respectively.