A comparison of a transdermal eutectic lidocaine/prilocaine cream and subcutaneous lidocaine injection prior to jugular vein catheterization in horses: a randomized crossover study.

Overview

• This study compared the pain and behavioral reactions of horses to two different local anesthetic methods—transdermal application of a 5% lidocaine/prilocaine cream (EMLA) and subcutaneous injection of 2% lidocaine—prior to jugular vein catheterization.
• The goal was to determine which method caused fewer adverse reactions and could serve as an effective alternative for numbing the area before catheter insertion.

Study Design and Methods

• Type of study: Randomized, blinded crossover trial involving university-owned research horses.
• Subjects: 26 horses participated.
• Procedure: Each horse received both treatments but on opposite sides of the neck (jugular sites), with at least 12 hours between procedures to avoid interference.
• Treatments:
  • On one side, 1 g/cm of 5% lidocaine/prilocaine eutectic mixture of local anesthetics (EMLA cream) was applied 60 minutes before catheterization.
  • On the contralateral side, 1.5 mL of 2% lidocaine was injected subcutaneously 15 minutes before catheterization.
• Catheterization: A 14-gauge catheter was inserted percutaneously at each treatment site and left in place for 20 minutes.
• Behavioral assessment: Four blinded evaluators scored horses’ aversive behavior at two points—during treatment application and during catheterization—using a simple descriptive scale (SDS).
• Local site assessment: After treatment and catheter removal, sites were evaluated for skin reactions (erythema, blanching) and pain immediately, at 20 minutes, and 24 hours post-removal.
• Statistical analysis: Behaviors were analyzed using stratified multivariate Mann-Whitney U tests, with significance defined as p < 0.05.

Key Findings

• During anesthetic application: Horses displayed significantly less aversive behavior (lower SDS scores) when EMLA cream was applied compared to lidocaine injection.
  • EMLA mean score: 0.3 ± 0.3
  • Lidocaine injection mean score: 0.5 ± 0.4
  • Statistical significance: p = 0.012
• During catheterization: Horses treated with lidocaine injection tended to show lower aversive behavior scores compared to those treated with EMLA cream.
  • Lidocaine injection mean score: 0.4 ± 0.4
  • EMLA mean score: 0.8 ± 0.5
  • Statistical significance: p = 0.006 initially, but this was not significant when adjusted for the side of catheter placement (p = 0.077).
• Local reactions: Neither the EMLA cream nor the lidocaine injection produced adverse reactions like redness, blanching, or pain at application sites immediately or up to 24 hours following catheter removal.

Interpretation and Implications

• Tolerability: The transdermal EMLA cream caused fewer immediate aversive reactions during application compared to lidocaine injection, implying it is less painful or irritating to apply.
• Efficacy: Although lidocaine injection seemed to have slightly better results during the catheterization itself, this difference was not statistically robust after adjustment, suggesting both methods effectively provide local anesthesia.
• Clinical relevance: EMLA cream offers a non-invasive, well-tolerated alternative to injections for local anesthesia prior to jugular catheter placement in horses, potentially improving animal comfort and ease of handling.
• Safety: No adverse skin reactions affirm the safety of using EMLA cream as a topical anesthetic in equine patients.

Summary

• The study supports the use of a 5% lidocaine/prilocaine topical cream as a viable and less aversive alternative to subcutaneous lidocaine injections for numbing the jugular vein area before catheterization in horses.
• This could lead to improved welfare during such routine veterinary procedures by minimizing pain and stress responses related to local anesthetic administration methods.